ALBERT

Notes: An early segregation of germ cells and migration through a germ track into the gonad does not occur in the albino rat. The germ cells are produced only from the peritoneum of the genital region and their earliest formation is coincident with the thickening of the coelomic epithelium to form the genital ridge. This takes place eleven days after insemination in embryos of approximately 18 somites. Germ cells continue to form from the peritoneum during the early development of the gonad. The peritoneum of this region also produces mesenchyme, smaller cells of the gonads, and the germinal epithelium.The argument for the specific character of the germ cells in vertebrates and their continuity from the egg is based largely upon assumption, and not upon substantial observations, and must be discarded. Germ-cell origin is a problem of cellular differentiatio, and not of early segregation.

Notes: Painted turtles, gopher tortoises, and terrapins were fed on various mixtures of sand, salts, dextrin, casein, cod-liver oil, wheat, eggs, lettuce, and meal worms. Each individual was weighted weekly for about a year and then killed for analysis, the water, ash, nitrogen, and fat being determined. Some individuals increased in weight as much as 75 per cent, others lost weight. Judged by growth and chemical analyses, the food requirements of chelonians, as representative poikilothermal vertebrates toward nutritive substances (including vitamines) are similar to those of homoiothermal animals.

Notes: Of the eggs laid by Fasciolaria about 1 per cent develop into veligers, about 2 per cent more undergo a few cleavage divisions, and about 97 per cent do not divide at all. The 99 per cent that fail to develop normally are ‘swallowed’ by the veligers. This study concerns itself chiefly with the ova that do not divide. Notes on normal development and on the ova that undergo atypical cleavage are included.All of the ova are found to be typical when passed from the ovary. To each ovum one to several sperms become attached at the vegetal pole in the region of a mass of undifferentiated protoplasm - the ‘polar mass.’ A fertilization cone forms in each ovum and a fertilization membrane. In typical development a yolk lobe is formed, the sperm enters in the usual way, and fertilization is completed as in many other mollusks. In 97 per cent of the ova the yolk lobe is not formed and the sperm does not enter. In these cases the wall of the egg nucleus remains intact a long time. The nucleus itself and the ‘polar mass’ sink into the egg and meet at the center. Then the nuclear wall disappears and an atypical diaster is formed. However, cleavage is not begun and the chromosomes form vesicles that remain near the center of the ovum until it is ‘swallowed’ and digested by the veliger.

Notes: A special type of cell, called ‘Lichtzellen’ by Hesse, was found in the photosensitive regions of the earthworm. Wherever the epidermis is most sensitive to light these cells are most abundant. They are found in the epidermis of all segments of the body and also in nerve enlargements of the prostomium and the caudal segment, but the intersegmental and ventral regions of the different segments, except the more distal ones, contain none of them. They are supplied by nerves and each contains a characteristic inner structure, the optic organelle, composed of a large central hyaline structure, the lens, which is surrounded by a dense network of nerve fibrillae, the retinella. In hanging drops the lens was found to focus light in the region of the retinella irrespective of the direction of the rays.These cells are similar in structure and function to the visual cells in leeches. Available data indicate that these cells function as photoreceptors and that the fibrillae of the retinella are the direct receptors of light stimuli.Pigment is not associated with the photoreceptors in a way that suggests direct functional relationship, but there is a subepidermal pigment layer through which pinhole windows admit light along the path of nerves to each of the nerve enlargements containing photoreceptor cells. These windows open in such directions as to determine the direction of withdrawal of the worm.

Notes: The effect of removal of the liver has been noted in fishes, frogs, and turtles. As in the higher vertebrates, removal of the liver produced a fall in blood sugar and a loss in muscular tone. The lower vertebrates failed to respond to intravenous injections of glucose, as do the birds and mammals. They also fail to respond to maltose or levulose. The liver maintained the blood-sugar level in the lower vertebrates, which is necessary for the maintenance of life.The mechanism of carbohydrate metabolism in the lower vertebrates may be different from that in the higher ones, in that glucose, when injected intravenously, apparently exercises a progressively less beneficial effect on the characteristic hypoglycemic condition which follows the removal of the liver of mammals and cold-blooded vertebrates.

Notes: This paper reports experiments with Fundulus heteroclitus to modify larval development by means of ultraviolet radiation. Eggs were exposed to radiation at various intervals after fertilization for varying periods of time. The results accord with previous work on fish teratology, and the developmental types obtained are essentially similar to those produced by chemicals, cold, and hybridization. The deviations from normal development occur in the same body regions as do those in other vertebrates whose early development has been modified by the action of radiation (x-rays, radium, etc.).The results of these experiments indicate that there is a non-specificity in susceptibility relations with the production of similar types of monsters for widely different reagents. That these eggs are differentially susceptible to the action of ultraviolet radiation is indicated by the fact that those regions which have the highest metabolic activity when an inhibiting influence is active are the ones most generally affected. Thus modifications of the nervous system, sense organs, circulatory system, tail region, and body axis result, respectively, in the production of varying degrees of cyclopia, inadequate circulation, short, stubby or bent, non-motile tails (some bifid), and anterior twinning.As these modifications may be produced by applying inhibiting influences during the first few minutes after fertilization, it is evident that there is in the egg at this stage some constitutional or physiological basis which determines early differences in susceptibility of its various parts.

Notes: Projection microradiography was used to determine the density and orientation of the force transmitting structures, i.e., trabeculae and bone lying between approximately parallel vascular canals, within the bones of cat skulls. The organisation in the skulls was confirmed statistically for a total of ten cats. The results of the observations showed that within specific areas of the skull a high degree of structural orientation and an increased density of osseous structures was present. The distribution of these characters corresponded in contiguous bones such that a continuum of structural organisation was established between the alveolar region and the site of attachment of the temporalis and masseter muscles and the glenoid region.The patterns of force transmission during jaw closure were determined when a resistance was placed initially between the canines and then the carnassials. An analysis was first carried out on dry skulls using colophonium resin to determine the direction of the force distribution. The nature and the approximate magnitude of the forces were ascertained by replacing the resin with strain gauges. The basic similarities in the strain patterns recorded from the dry skulls and those from the ten anaesthetised cats in which strain gauges had been intra-vitally implanted, substantiated the recordings made on the dry skulls. Combination of the results from the three sets of experiments defined the patterns of force distribution in the cat skull during the closure of the mandible against a resistance. The results showed that: (1) the combined action of the temporalis and masseter muscles tended to reduce the overall strain in the skull bones, and that the deformations produced by the action of the masseter were greater than that exerted by the temporalis muscles; (2) during biting, whether the resistance was placed between the canines or carnassials, compressive forces predominated in the facial bones; (3) small movements observed between facial bones indicated the presence of a flexible component within the skull, thus allowing large forces to be exerted during biting without overstressing the facial bones; (4) the glenoid fossa is part of a force bearing joint; (5) forces generated during biting were resisted within the skull by forces of an opposite nature generated within the system, the incompressible nature of bone and by the effect of the soft tissues; (6) the nature and the magnitude of the strain altered when a resistance was placed at the canines and then at the carnassials; however, the pattern of force distribution within the skull remained the same; (7) there was a direct correspondence between the detailed structural organisation of the bones and the patterns of force distribution. This conclusion would appear to apply in general to mammalian skulls. The study also emphasises the importance, neglected hitherto, of carrying out a variety of experiments to determine the patterns of force distribution in bones.The Trajectorial Theory of bone organisation is discussed and, on the basis of the results obtained, a modified theory is proposed. This states that: the structural continuum is common to the compact and cancellous bone and comprises bony bars which are aligned in the optimum direction for the transmission of force to a region in the bone or bones where it is effectively resisted.

Notes: The tarsi of all three pairs of legs of both sexes of Aedes aegypti (L.) bear spine sensilla, five types of hair sensilla, which are designated A, B, C1, C2 and C3, and campaniform sensilla. Type A and B hairs, spines, and cam-paniform sensilla are innervated by one neuron with a tubular body, a characteristic of cuticular mechanoreceptors. In particular the hairs and spines are tactile receptors and the campaniform sensilla are proprioceptors. The C1, C2, and C3 hair sensilla have the morphological features of contact chemoreceptors. Type C1 and C3 hairs are innervated by five and four neurons, respectively, which extend to the tip of the hair. Type C2 is innervated by five neurons, one of which terminates at the base of the hair in a tubular body while the remaining four extend to the tip of the hair. The role of the type C hairs in oviposition behavior, nectar feeding, and recognition of conspecific females is discussed. Presumed efferent neurosecretory fibers occur near the spine and hair sensilla.

Notes: The micro-anatomy of the corpuscles of Stannius of the toadfish, Opsanus tau, an aglomerular marine teleost, has been studied by light and electron microscopy. The corpuscles are composed of extensively anastomosed cords of epithelial cells which maintain intimate contact with blood capillaries. Most of the epithelial cells contain acidophilic granules which also show a positive reaction with the periodic acid-Schiff technique and aldehyde fuchsin. On the basis of fine structural criteria, three cell types can be recognized. The granular cells contain abundant quantities of granular endoplasmic reticulum, ribosomes, Golgi apparatus with prosecretory granules, coated vesicles, polymorphic mitochondria with lamellar cristae, filaments, microtubules, a cilium, a variety of lysosome-like dense bodies, glycogen particles, lipid droplets, secretory granules and intranuclear lipid-like inclusions. One variety of agranular cell (type I) is characterized by the total absence of secretory granules, but it contains large amounts of granular endoplasmic reticulum and ribosomes, conspicuous profiles of Golgi apparatus, coated vesicles and sometimes an abundance of glycogen. Another variety of agranular cell (type II) has poorly developed cytoplasmic organelles. The perivascular space between the capillary and parenchyma contains connective tissue cells and abundant nerve fibers. The different types of epithelial cells observed in the corpuscles of Stannius of this fish may represent functional stages of the secretory cycle in a single cell type.

Notes: The nervous system of the maldanid polychaetes Clymenella torquata (Leidy) and Euclymene oerstedi (Claparede) (= Caesicirrus neglectus [Arwidsson, '11-'12]) retains its primitive association with the epidermis. It shows only slight metamerism in the presence of larger collections of neurones opposite the parapodia and of larger nerves at the segmental boundaries. Multicellular giant fibers are present in the ventral nerve cord; giant neurones which show a characteristic pattern of distribution in each species are also present. The cerebral ganglia supply nerves to the prostomial wall, nuchal grooves and the wall of the buccal cavity, and a pair of large nerves from the circumpharyngeal connectives also appear to join the buccal system. The organs of special sense are the elongated prostomial nuchal grooves, and prostomial ocelli in Euclymene but not in Clymenella. Statocysts are absent.Four pairs of nephromixia are present. They lie in the aseptate anterior trunk, in chaetigers 5-9 of Clymenella, and 6-10 of Euclymene. The nephridiopores lie at the ventral ends of the neuropodia of chaetigers 6-9 and 7-10, respectively. Each nephromixium consists of coelomostome, tubule and contractile bladder. The wall of the tubule and bladder consists of both excretory and ciliated cells. Most of the cytoplasm of the latter forms a bounding layer at the outer surface. The cytoplasm of the excretory cells contains lipid material and appears to synthesize lipofuscin. The tips of the excretory cells swell, fill with granules, and break off in the form of vesicles which are periodically expelled in clouds from the nephridiopores. Glycogen is present, especially in the ciliated cells of the tubule and coelomostome.Granules of a lipoid nature accumulate in (or between) cells of the nephridia, epidermis, and some regions of the gut, and may be excretory. Lipid granules also appear to be synthesized by coelomocytes which eventually end up in masses in the ventrolateral coelomic cavities of the tail.The nephridia act as gonoducts, but show no seasonal variation in either size or histological structure.

Notes: The ascophoran Pentapora foliacea was studied from epoxy sections of skeletal and soft (hard-soft) tissues. The basal wall is double, indicating the colony grew as two independent layers, back to back. The structure of the vertical walls and interzooidal communication organs indicates that zooids were budded in the usual way as in most encrusting cheilostomes. Secondary layers of the frontal wall are of acicular aragonite. The ovicell develops as a flattened cuticular bladder in early ontogeny; the aragonitic layer of the frontal wall later engulfs it. A median vesicle, an evagination of the vestibular wall, is present but the eggs may be supplied with sufficient yolk to nurture the embryo. The overall ovicell structure is similar to that of hyperstomial ovicells in other cheilostomes.

Notes: This investigation describes the pre-natal morphogenesis of the type I pneumocyte subsequent to its differentiation from pulmonary epithelium. Cells lining subpleural alveolar septa were photographed from serial sections with the electron microscope, and a three-dimensional representation of each cell was obtained by transferring the contours of the cell membranes from montages to transparent plastic sheets which were then spaced to scale and stacked. The results of this study indicate that: The nascent blood-air barrier of a 50-day reconstructed cell was twice as thick as the average definitive barrier; definitive barrier thickness was observed in some areas in a 63-day reconstructed cell; the amorphous component of elastic tissue which appears peripherally in septal connective tissue during pre-natal morphogenesis may be directly juxtaposed to the basal lamina of the alveolar epithelium; the orientation of the cell junction between a pneumocyte and its neighboring cells, as observed in sections of alveolar septa, changes as the contour of the pneumocyte changes from simple abutment to overlapping patterns.

Notes: The fine structure of the mid-gut musculature of the desert locust, Schistocerca gregaria is described and compared with that of the visceral muscles of other species. The gross morphology and fine structure of the nervous system which supplies the mid-gut muscle fibres is described.

Notes: The integument of Paranthessius anemoniae has been studied with light and electron microscopy. A cuticle with clearly defined epicuticular, exocuticular and endocuticular regions overlies a cellular hypodermal layer. The distribution of carbohydrate, lipid and protein components of the cuticle were demonstrated histochemically. Parabolic striations in oblique sections of cuticle suggest that its molecular architecture fits a “twisted sheet” theory proposed for other species.Arthrodial membranes at body and limb joints have a homogeneous structure, lacking exocuticle and endocuticle. Subcuticular glands appear to secrete substances thought to be responsible for the immunity which Paranthessius seems to have to the nematocysts of its host. Small hairs, situated in cuticular cups which occur over the dorsal body surface are considered to function as rheoreceptors.

Notes: The larval epithelium of the sea urchin, Lytechinus pictus, consists of squamous cells and bands of columnar epithelial cells bearing cilia. During metamorphosis this tissue undergoes a series of rapid, complex changes. Through the scanning and transmission electron microscope, we describe and analyse these changes. The changes can be divided into three steps. (1) The larval arms bend away from the left side of the larva, exposing the urchin rudiment. Cells which are identical to smooth muscle cells are in a position to bring about this bending. (2) The squamous epithelial cells assume a cuboidal shape. This change in shape results in the collapse of the larval epithelium onto the presumptive aboral surface. These cells possess a subapical band of microfilaments. The cellular shape change but not the bending of the arms is reversibly inhibited by Cytochalasin B. These observations suggest a mechanism for this change. (3) The former lining of the vestibule of the urchin rudiment comes to lie over the collapsed larval tissue and forms the adult epithelium. At this point, after only one hour, the larva has assumed the external shape of an adult sea urchin.

Notes: The mucous gland of the red-spotted newt, Notophthalamus viridescens viridescens, Rafinesque was examined by histochemical and ultrastructural techniques and its cytological responses to various hormonal conditions were studied. Its secretory epithelial cells produce and release in merocrine fashion a neutral, unsulphated mucosubstance. The secretory epithelium is bounded peripherally by a thin, but apparent non-functional, myo-epithelium. The duct of this mucous gland consists of a single keratinized tubular cell that extends from the neck region of the gland to the surface of the epidermis.Mucous secretion is absent or greatly reduced on the skins of newts maintained under laboratory conditions for a few weeks but reappears after injection of ovine prolactin. Mucous glands in laboratory conditioned animals show a 4-fold increase in volume brought about by the engorgement of their epithelial cells with secretory granules. Ovine prolactin reduces the volume of the glands to unconditioned levels with a corresponding reduction in granular content, suggesting that prolactin functions in the release of the granules. This view is reinforced by the findings that autotransplantation of the pituitary gland prevents the conditioning effect and that glandular volume increases in auto-transplanted animals given ergocornine. Granular accumulation begins also in hypophysectomized newts but ceases after a week, indicating the need for some hypophyseal factor in the synthesis as well as the release of the granules. Ovine prolactin restores mucous glands of hypophysectomized newts to the unconditioned state. Contrary to earlier findings, ovine prolactin induces a reduction in the volume of the mucous gland in thyroidectomized newts.

Notes: The process of coelomic pouch formation in Pisaster ochraceus was studied with light microscopy, transmission and scanning electron microscopy and time-lapse cinemicrography as well as with the drug cytochalasin B. As in most asteroids, the paired coelomic pouches of Pisaster ochraceus are formed from outpocketing of the archenteron.Arrays of 50 Å microfilaments are found in the presumptive coelomic pouch cells at the apex of the archenteron as well as in the filopodia of the mesenchyme cells. Both cell types undergo active movements throughout the entire process. Treatment of embryos with cytochalasin B (CCB) during coelomic pouch formation results in the loss of cell movements and the regression of the coelomic pouches; this is accompanied by the loss of microfilament arrays in both cell types. Cell movements and microfilament arrays reappear on removal of CCB and coelomic pouch formation resumes.Our evidence suggests that the microfilaments in the presumptive coelomic pouch cells provide the main force for the outpocketing movement. The major role of the microfilament arrays in the filopodia of the mesenchyme cells associated with the coelomic pouches is to determine the definitive shape and location of the pouches.

Notes: Morphological changes of the ovary of the Chinese cobra, Naja naja, throughout the annual reproductive cycle are described. A single clutch of between 6 and 22 eggs is produced in late June. From July to the following April the ovary remains quiescent and contains small previtellogenic, hydration stage follicles. The growth of an ovarian follicle from a primary oocyte to maturation and ovulation is estimated to take three years. The histology of the germinal epithelium and the follicular granulosa shows seasonal changes correlated with the growth of the oocyte. During the quiescent period, the germinal epithelium lacks mitotic activity, but during April, when yolk deposition and rapid growth of the preovulatory follicles take place, the germinal epithelium shows intense mitotic activity. The growth of the smallest hydration stage follicles, and the occurrence of cytoplasmic bridges between the pyriform cells of the granulosa and the developing oocyte, also appear to increase during this period. The possible function of the pyriform cell is discussed and the literature on the origin and fate of these cells in the squamate ovary is reviewed. Postovulatory follicles (corpora lutea) and two types of atresia are described and compared with what is known of these structures in other reptiles.

Notes: An experiment was undertaken to determine which sensory structures of the mouse embryo inner ear developed from what portion of the mouse otocyst. Otocysts of gestation days 10, 11, 12 and 13 were divided by surgical dissection into six anatomical groups: dorsal, ventral, anterior, posterior, medial and lateral halves. They were organ cultured separately. After a period of ten days, the explanted tissues were harvested and processed histologically for microscopic analysis. The surgical control specimens fixed at the time of explanation were composed of undifferentiated ectodermal cells for tissues of gestation days 10, 11, and 12. Otocysts of gestation day ten showed no gross morphological differentiation. Otocysts of gestation days 11 and 12 showed, during the course of their subsequent growth, that the three semicircular ducts and their associated cristae developed from the dorsal and lateral halves. Only the anterior and posterior canals and cristae originated from the medial portion. The posterior half gave rise to the posterior crista and the anterior half provided for the development of the anterior and lateral cristae. The cochlear duct and its sensory epithelium developed in all the anatomical groups except the dorsal half. The utricle developed in the dorsal section of the middle third of the otocyst, while the utricular macula developed in the anterior half of the same section of the otocyst. The saccule and its macula differentiated from the ventral section of the middle third of the anterior half.

Notes: The pineal-paraphyseal complex of sea turtles is an impressively large structure which projects dorsally and anteriorly above the prosencephalon. The complex was examined by light microscopy in several age classes of green sea turtles (Chelonia mydas) and from juvenile loggerhead turtles (Caretta caretta). The paraphysis is extensively fused to the distal portion of the pineal body, suggesting an interrelated function for these two tissues. No duct or canal was observed connecting the pineal lumen to the third ventricle. Two pineal cell types are described which appear to correspond to the neuroglial supportive cells and the secretory rudimentary photoreceptor cells of other amniotic vertebrates. A possible luminal secretion in the form of apical protrusions is produced by the latter cell type. No typical photoreceptive outer segments were observed.

Notes: The fine structure of the wax gland of Anomoneura nymph and its metamorphic change were investigated. In the nymph, this organ encircles the anus, and consists of two kinds of cells, derived from epidermal cells: (1) very tall, slim wax cells, which produce and secrete the wax, and (2) flat interstitial cells found among the wax cells. The whole gland is covered by a wax-secreting cuticle with a delicate surface sculpture. Each wax cell has a long, wide duct which opens at the cuticle and penetrates the entire cell. Its cytoplasm is rich in mitochondria and smooth endoplasmic reticulum while that of interstitial cells contains rough endoplasmic reticulum. During each nymphal molt, the cluster of primordial wax gland cells  -  derived from the epidermis  -  proliferates rapidly and forms the gland of the next instar. The gland of the preceding instar meanwhile degenerates. Interstitial cells play an important role in cuticle formation and shedding at each molt. These cells alone produce and deposit the new cuticle of the next instar; the wax cells, specialized for wax production, cannot produce cuticle. The apical portion of the wax cell is cut off from the main cell body by growth of the surrounding interstitial cells. Thereafter, the wax cells degenerate, resulting in the rapid disappearance of the previous instar's wax gland. Adults lack this gland entirely.

Notes: The dorsal ventricular ridge (DVR) is a subcortical, telencephalic structure in reptiles and birds that protrudes into the lateral ventricle. The structure of DVR has been studied in the red-eared turtle (Pseudemys scripta elegans) in Nissl and Golgi preparations. The DVR in Pseudemys is divided into the anterior dorsal ventricular ridge (ADVR) and the basal dorsal ventricular ridge (BDVR) by the dorsal branch of the middle ventricular sulcus. The structure of ADVR has been examined in detail.The ADVR is divided into four regions with distinct boundaries termed dorsal area, medial area, ventral area and central area. Dorsal area, medial area and ventral area border on the lateral ventricle; central area lies deep to the other areas. Three classes of neurons are found in Golgi preparations of ADVR. Juxtaependymal cells have somata near the perikarya of ependymal cells; their dendrites are found primarily in a periventricular fiber zone. Aspiny neurons were observed only in the dorsal half of ADVR and appear to be restricted to deep regions of the ridge. These multipolar neurons are rarely encountered in Golgi preparations, and the observed distribution may not represent their actual distribution in ADVR. The majority of the cells observed in ADVR are spiny neurons with dendritic fields that range from stellate to double-pyramidal. Cells in this class may be subdivided on the basis of axonal morphology into at least two groups, but further studies are needed to determine the range of axonal morphology exhibited by these neurons.An analysis of the distribution of these cell types in Golgi material shows that dorsal area, medial area and ventral area are organized in four zones concentric with the ventricular surface. Central area apparently lacks a concentric pattern of organization. Zone 1 is a periventricular fiber band that contains juxtaependymal neurons and ascending dendrites of zone 2 spiny neurons, and it may serve as a structural substrate for segregated input onto these cell populations. Zone 2 contains clusters of spiny neurons with apposed somata, which vary in size and distribution between areas. Dendrites of zone 4 neurons are also found in the deep half of zone 2. Zone 3 is a cell-poor region which lies at the center of a region of overlapping dendritic fields of zone 2 and zone 4 neurons. Zone 4 contains predominantly spiny neurons (aspiny neurons are found only in the dorsal half of ADVR) which are either isolated or in small clusters with apposed somata. Dendrites of zone 2 cells extend superficially into zone 4, so that the deep portions of zone 4 may be a substrate for segregated input to zone 4 neurons. These zones are differentially elaborated in each area. Central area, by contrast, consists of scattered spiny and aspiny neurons among fibers connecting ADVR and the lateral forebrain bundle.A comparison of these findings with the ADVR of snakes (Ulinski, '78a,b) shows both similarities and differences in DVR organization in the two taxa. Although snakes lack areal divisions, ADVR is organized in four concentric zones (zones A-D). Zones A and B resemble zones 1 and 2 in turtles, consisting of a superficial fiber zone and a subjacent cell cluster zone. The clusters are smaller in snakes than in turtles. However, snakes lack a cell-poor band deep to zone B, and dendrites of cells in zone C enter zone A. Thus, there are differences in both areal and zonal dimensions of ADVR organization in turtles and snakes.

Notes: Ultrathin sections of the nasal barbel of the channel catfish, Ictalurus punctatus, were studied in the electron microscope and the fine structure was compared to that of barbels of other teleosts and to the mandibular (dentary) barbels of I. punctatus. While the overall histology of the nasal barbel is similar to that of barbels described previously, this study revealed far greater cellular complexity and variability than was previously reported. A layer of stratified epidermal cells rests upon a connective tissue dermis containing a cartilage rod, a large number of nerve fibers and numerous blood vessels, fibroblasts and pigment cells. Taste buds are present in the epidermal layer. This layer was found to contain probably 16 kinds of cell types, several of which may represent transitional stages, in addition to taste bud cells. Observations were made pertaining to innervation and cell types in the taste buds. A new terminology for designating the barbels of I. punctatus is suggested.

Notes: New data on the brain of Latimeria indicate that previous estimates of the brain weight were too high by a factor of two. Our data suggest a brain weight of 1.1-1.5 grams for a specimen with a body weight of 30 kilograms. Quantitative data on major divisions of the brain are presented for the first time, and the relative size of the major brain divisions is similar to that of sturgeons and generalized sharks (such as hexanchids and squalids). Examination of brain component weight (s): body weight plots in a sample of non-teleost actinopterygian fishes indicates that all major divisions of the brain, except the telencephalon, are larger than in Latimeria. Brain component sizes in Latimeria are more similar to those extrapolated for amphibian brains than to those for actinopterygians. However, the cerebellum of Latimeria is considerably larger than that of amphibians.

Notes: The Champy-Maillet osmium tetroxide-zinc iodide technique and a new method using azur B-sodium thioglycolate were used to study the general nervous tissue structure in planarians. A subepidermal and a submuscular nerve plexus, partially reported by earlier authors, are described, and a gastrodermal plexus is reported for the first time in triclads. The possible functions for each one of these plexuses are discussed. By the Champy-Maillet method, the innervation within the parenchyma appears as an array of numerous single nerve fibers that course between the parenchyma cells making apparent synaptic contacts. The pharynx has outer and inner nerve nets similar in structure to the submuscular nerve plexus. Both nerve nets are connected to each other by radial nerves.The central nervous system has a sponge-like structure with many lacunae filled with cell bodies, dorso-ventral muscle fibers, parenchymal cell processes and excretory ducts. The existence of this sponge-like nervous tissue structure is discussed in relation to the still incomplete centralization of the nervous tissue in these organisms, to the lack of a true vascular system and to the acoelomate level of organization. A comparison with the nervous tissue structure of more advanced groups like polyclads and nemertines is suggested.

Notes: Secretion in the salivary glands of Gromphadorhina portentosa involves three cell types: parietal cells, secretory cells, and duct cells. The organization and role of the parietal and secretory cells are here considered. Parietal cells have numerous mitochondria, indicating an active metabolic role and the subsequent production of ATP. Plasma membrane invaginations and intracellular ductules containing microvilli appear to function in the absorption of solutes from the hemolymph and finely-tapered ductules. Secretory cells contain abundant rough endoplasmic reticulum, the three forms (stacked, vesicular, and diffuse) of which appear to develop sequentially during maturation. Secretory vesicle formation is asynchronous between adjacent secretory cells, and apparently the large vesicles often coalesce. The secretory vesicles also show differing degrees of electron density, indicating distinct biochemical composition.

Notes: Studies were undertaken of the microcirculation and histology of the gill of Protopterus aethiopicus as a prerequisite for elucidating the function of the gills in a bimodal respiratory system. The lamellae of the gill-bearing arches (I, IV, V, VI) resembles the arborescent external gill of the larval amphibian rather than the gill of the teleost or selachian.The arterio-arterial system (a-a) of the gill consists of an afferent artery, a series of large capillaries, and an efferent artery on each of the primary, secondary and tertiary lamellae. There are no pillar cells and the loose capillaries are covered with a multilayered epithelium. While living in water, the minimum distance for gas exchange is of the order of 5 μ. An afferent-efferent arterial shunt at the base of each primary lamella may be involved in control of lamellar blood flow and the resistance of the gill vasculature.The arterio-venous system originates primarily from the efferent side of the arterio-arterial system and drains into large branchial veins. Numerous contractile cisternae, interposed between intercellular channels and veins, presumably function as micropumps that collect fluid from intercellular epithelial spaces and inject it into the venous circulation.During aestivation, the epithelial layer of the gill lamellae becomes thinner. The entire gill vasculature, including the capillaries and afferent-efferent shunts on arches IV-VI, are very dilated which presumably promotes blood flow through these gill arches to the lungs.

Notes: The movements of the shoulder girdle of eight adult cats during overground stepping were studied, using standard slow motion cinematographic techniques. The patterns of activity of shoulder muscles were examined, using simultaneous intramuscular electromyography. Walking, trotting and galloping steps were analyzed from digitized single motion picture frame images. Angular movements of the shoulder girdle consist of biphasic flexion and extension of the shoulder joint and a monophasic flexion-extension alternation of the scapula on the thorax during each step cycle. In addition, the center of the scapula moves craniad during the swing phase and caudad during the stance phase with respect to a fixed reference point on the animal. Similar vertical movements of the center of the scapula also occur in each step cycle. Results of EMG studies of the 17 muscles capable of acting on the shoulder girdle indicate that three overall patterns of activity are found: (1) a pattern typical of extensor muscles, active during all the extension epochs; (2) a pattern typical of flexor muscles, active during the flexion epoch; and (3) a biphasic pattern of activity, active twice in each step. These data are used, along with a re-examination of previous models of the mechanics of the shoulder girdle of carnivores to examine the function and mechanics of shoulder motion. It is concluded that the rotary and translatory movements of the shoulder girdle during stepping combine to enhance step length.

Notes: The most striking morphological feature of the ovarian epithelium of Cymatogaster is the presence of intercellular dilations during much of the year. These dilations increase markedly in volume during the several months prior to ovulation and fertilization, and decrease in volume during the months of embryogenesis and gestation. The epithelium then returns to its initial, relatively undifferentiated state. The extracellular material within the dilations likely is synthesized in the cells adjacent to or within the dilations. Apparently most of this material is released into the ovarian lumen when the apicolateral margins of adjacent epithelial cells pull apart; possibly it serves as nutrient for developing embryos.In addition to supporting embryogenesis, the ovarian epithelium also apparently is involved in sperm storage. Sperm are maintained within pockets in the ovarian epithelium for the several months between insemination and fertilization. The cells lining the sperm pocket do not develop the intercellular dilations characteristic of most of the ovarian epithelium, and sperm remain associated only with the sperm pocket cells.

Notes: The antennae of Folsomia candida and Hypogastrura copiosa are provided with tactile hairs on all four segments and, in addition, with chemoreceptors on segments three and four. The cuticle of the thin-walled chemo-receptors of Folsomia, as in most other insects, is penetrated by many small pores uniformly distributed over the surface. In contrast, the cuticle of the thin-walled chemoreceptors of Hypogastrura is unusual in that a band of cuticle without perforations spirals around, or partly around, the hair. The cuticle between the spirals is very thin, and has extremely small openings in it. The tip of the antenna of Folsomia is thin, permeable to dyes in aqueous solution and apparently glandular. The antennal tip of Hypogastrura is definitely glandular.

Notes: After hemisection of the spinal cord and medulla oblongata, a projection has been traced to the inner half of the tectal white of the tiger salamander, using Fink-Heimer degeneration staining. By microelectrode recording it was found that the tectal projection forms a topographic somatosensory map of the contralateral half of the body. This map is in register with the overlying retino-tectal visual projection. Using the Falck-Hillarp technique, it was found that the somatosensory tectal input is associated with yellow-fluorescing 5-hydroxytryptamine fibers.

Notes: A comparative morphological study concerning typology and topography of chemoreceptors on the prothoracic legs of Calliphora vicina, Phormia terranovae and Musca domestica has been carried out. The typological criteria of Grabowski and Dethier ('54) and Hansen and Heumann ('71) were used. A single criterion, the shape of the tip, was used to define the different types of chemoreceptors.A-hairs have a rhombic pore at the side of the tip; B-hairs have an oval pore at the tip apex and D-hairs have a rectangular pore under an undulated, cap-like structure at the hair tip. A-, B-and D-hairs were found in the tarsomeres of Phormia; in Musca and Calliphora only B- and D-hairs were found. An opening and closing mechanism may operate on the pores of the tips of the chemoreceptors. Chemoreceptors were counted and a topographical map was completed, using SEM-techniques. Topographical maps are of value in electrophysiological and behavioural research, where only a limited optical magnification is possible.

Notes: The structures of the lantern tracheoles of three genera of flashing fireflies are compared. All three genera have stiff, reinforced tracheoles which resist folding or collapsing under conditions which flatten more typical tracheoles. This common specialization supports the hypothesis that the tracheoles play a major role in flash control in these fireflies, especially as the morphological basis of the stiffening is different in the three genera. Study of the tracheoles of other tissues reveals that there is great variety in structure and flexibility of these vessels from tissue to tissue and organism to organism, suggesting that tracheolar specialization may be a general phenomenon, with the fine structure of these air tubes being tailored to the particular demands and conditions of the tissues in which they are found.

Notes: Tibiotarsal segments of 12-day chick embryos homozygous for the crooked neck dwarf gene (cn/cn) were examined histologically following routine methods of preparation. The myogenic mass fails to divide into separate muscle bundles during the early stages of differentiation. Myoblasts and myotubes are observed, although the proportion favors the mononucleate cell population. Multinucleate myotubes are often wavy in appearance and many contain eosinophilic cytoplasmic inclusions. The entire tissue mass of mutants appears more compacted than in control limbs. Poor organization of muscle appears related to the lack of a suitable connective tissue system. Epimysia, perimysia, and subcutaneous connective tissue fail to develop properly. Tendons are poorly developed or absent. Comparisons between mutant and control embryos show no differences in peripheral innervation. Nerve fascicles penetrate deeply into the developing muscle of both species. The distribution of vascular elements is seemingly normal also. Skeletal muscle of cn/cn embryos is capable of differentiating to the myotube stage, after which it undergoes cellular degeneration without achieving a functional state. Comparisons of this mutant with alleged chemical phenocopies show important differences.

Notes: The histology and carbohydrate histochemistry of eight teleostean stomachs are compared. Three gross anatomical types of stomachs are described and their shapes appear to correlate somewhat with feeding habits. Each type can be divided histologically into a corpus and pylorus. Gastric glands, containing only one cell type, occur in the copora of all species, but are present in the pylori of esocids only. As a single cell can produce both enzymes and hydrochloric acid such cells may be comparable to those of amphibians but not mammals. Lamina propria and submucosa are indistinctly separated in corpora but better defined in pylori by an intervening muscularis mucosa. The arrangement of the muscularis into inner circular and outer longitudinal layers is the opposite of that seen in the esophagus. Gastric mucous cells show species variations in localization of epithelial mucosubstances, which in broad terms are recognized as sulfomucins, sialomucins and neutral mucosubstances. A piscivorous diet does not appear to demand any particular type of carbohydrate. Within the Centrarchidae, gastric pit cells vary in carbohydrate content from only neutral mucosubstance to only weakly acidic sulfomucin; two species contain both types. A positive PAS reaction on the surface of gastric epithelial cells is suggestive of a striated border and thus possibly absorptive function. The absence of stomachs in some teleosts and the evolutionary and dietary significances are discussed.

Notes: The American cockroach has a total of 368 muscles inserting on the post-coxal segments of its legs. By using a narrow morphological definition for delimiting individual muscles, it is shown (i) that the protrochanteral musculatures (23 muscles/leg) differ from the essentially identical meso- and metatrochanteral musculatures (24 and 26 muscles/leg) in number and disposition of extensors and in having a completely different flexor composition, and (ii) that the musculatures of the more distal segments of the legs are completely serially homologous, there being 2 muscles for moving each femur, 23 for each tibia, 7 for each first tarsomere, and 5 for each of the paired pretarsal claws. In all six legs, the trochanteral and tibial musculatures each contain single slender muscles that may be acting proprioceptively to measure the angular displacements between, respectively, the coxas and trochanters, and the femurs and tibias. Neurological and phylogenetic considerations are used to demonstrate why a narrow morphological definition should be employed, and why the widely used functional definition of Snodgrass ('35) is not only fallacious on evolutionary grounds, but also leads to making erroneous conclusions regarding the manner in which insect musculature is controlled by the insect central nervous system. Finally, it is hypothesized that the physiological limitations imposed by having an open circulatory system and the problems inherent in the neural control of large muscles may have been major evolutionary factors in forcing insects to use many slender muscles to control their body movements.

Notes: Among piscivorous cichlids consistent differences have been recorded between ambush and pursuit hunters with respect to electromyographic, kinematic, pressure and behavioral profiles during prey capture by high speed inertial suction. Piscivorous cichlids possess a repertoire of at least two patterns of prey capture, each of which is characterized by an extreme regularity of the kinematic, pressure, electromyographic and behavioral profiles. The nature and locomotory behavior of the prey, visually analyzed by the predator during the prestrike stalk, determine which of the two preprogrammed patterns is recruited. Agile and elusive prey invariably will elicit a preprogrammed motor output (stereotyped motor pattern) that produces the greatest suction velocities in both ambush and pursuit hunters. The greater the kinematic and suction velocities, the greater the overlap of the firing sequences of antagonistic muscle complexes. The opercular and branchiostegal apparati function as an exceedingly effective anti-backwash device, damping potential fluid oscillations within the oropharynx. Mastication occurs by triphasic movements and actions of muscles of the upper and lower pharyngeal jaws in both ambush and pursuit hunters. The lower pharyngeal jaw is acted upon by a force couple of which the fourth levator externus on one hand and the pharyngocleithralis externus and pharyngohyoideus on the other hand are the antagonistic components. Furthermore, the lower pharyngeal jaw is suspended by a muscular sling, the tension of which can be modified continuously. It is postulated that the switch from insectivorous to piscivorous feeding regimes (and perhaps vice versa) is accomplished by very minor structural and functional modifications, because the modulatory multiplicity and total range of repertories of the feeding machinery of the two trophic groups overlap significantly. Piscivorous cichlids may not have arisen by orthoselection in gradually-changing lineages, but represent the differential success of subsets from a random pool of speciation events. Adaptive features identified as characteristic for piscivory could have evolved in multiple and independent lineages at a punctuational mode and tempo.

Notes: The parasynaptic union of chromosomes associated with the formation of a karyosphere is demonstrated in the spermatocytes of Phanaeus.The twelve V-shaped leptotene threads are polarized with their apices embedded in one plasmosome-like body, their distal ends in another (primary and secondary caps, respectively), and undergo a conjugation of the parasynaptic type. The distal ends of the chromosomes are freed from their attachment in the secondary cap. The six pachytene loops retain their polarized configuration.The basichromatin of the pachytene chromosomes appears ultimately to be withdrawn to form the karyosphere comprising six chromatic bodies within an oxychromatic «plasmosome,» the latter probably derived from the primary cap. The two caps are believed to arise from the chromosomes. The primary cap apparently becomes incorporated again in the chromosomes; the secondary cap, together with linin remnants of the pachytene chromosomes, disintegrates in the nucleus as residual chromatin.In the dissolution of the karyosphere six ring-shaped tetrads emerge arranged in a temporarily connected chain, giving under certain conditions, the misleading impression of twelve components arranged end to end. The entire content of the karyosphere appears to be employed in the formation of the chromosomes; no visible plasmosome remains.

Notes: The primordial germ cells of urodeles and anurans can occupy comparable positions in the embryo only in very early stages of development, if at all. When first recognizable as reproductive elements, their situation in the two amphibian orders is quite strikingly different.The germ cells first become recognizable in urodeles in the medial edge of the lateral mesoderm; there is no evidence that their position previous to this time is other than mesodermal. In the anura they are entodermal in association during early development; they are finally separated from the dorsal portion of the roof of the archenteron to form a single axial germ-cell cord. No amphibian species studied showed a mode of origin different from that characteristic of its order.The so-called migration of the amphibian germ cells to their definitive situation is interpreted as the result of growth shiftings of related parts. Germ cells do not migrate independently through the tissues. Aberrant or ectopic cells for the most part result from failures or faulty correlations of growth processes. Certain aberrant cells of the caudal portion of the body in urodeles indicate the inclusion of sex elements in the ventral as well as in the lateral mesoderm.

Notes: The musculature of the ophidian head is a fairly complex structure, due to the specialization of the skull and the peculiar movements and motions made possible by the high degree of streptostylism.This musculature has been derived from the lacertilian type by a splitting and a shifting of the original elemental muscle masses of this group. Most of the muscles are clearly homologous with those of the Lacertilia. Some cannot be homologized by a study of the mature forms.The greatest differences lie in the separation of the muscle masses in the ophidia, as compared with the undivided masses in the Lacertilia. Since the jaw movements of the Lacertilia are rather simple, there is no need for any subdivision or splitting of the jaw muscles, but with the complex movements of the ophidia this becomes necessary.A few of the ophidian muscles appear to be neomorphs, as no key to their origin could be determined by a comparison with lacertilians.

Notes: Much more information than is available at present must be obtained before the phylogeny of the muscular system in the Teleostei can be worked out satisfactorily. As a step toward the solution of this problem, the present study gives a detailed description of twenty cranial muscles in a number of species belonging to three groups of cypriniform fishes: the Cyprinoids, Cobitoids, and Siluroids.Particular attention is given to the morphological relations of the following muscles: adductor mandibulae, geniohyoideus, levator arcus branchialis, adductor arcus palatini, retractor branchialis dorsalis, interarcualis dorsalis and the trapezius.Comparison is made between corresponding muscles in different members of the three groups of fishes, and various homologies are pointed out between muscles in cypriniform and those in other fishes, especially Amia, Scomber, Perca and Esox.

Notes: There are two discrete lobes comprising the armadillo subman-dibular gland. These two lobes can be defined grossly, histochemically and morphologically with the light and electron microscope. The minor lobe stains more intensely with PAS and AB. When viewed in the electron microscope, the secretory granules of the acinar cells within this lobe appear mucous-like. The granules of the demilune cells are slightly different in appearance. The secretory granules of the acinar cells in the major lobe contain many dense foci embedded in a fibrillar matrix, a substructure not described previously. The demilune cells of this lobe contain secretory granules with a mucous-like structure which is consistent throughout the entire lobe. As in the minor lobe, these demilune cells stain very intensely with PAS and AB.

Notes: End-plate distributions have been determined for three frog muscles of different morphology in order to relate end-plate topography to spatial muscle structure and nerve branching. Koelle's cholinesterase technique was applied, both on whole muscles and frozen sections. The end-plates of the short parallel-fibered cutaneus pectoris muscle appeared to be located in short bands along the nerve branches. The nerve tree is restricted to a zonal area across the middle part of the muscle. Depending on the way the nerve branches, the end-plate bands form innervation patterns, varying from one single continuous band to multiple distributed bands. In the latter case one frequently observes that different end-plate bands do not run across the same longitudinal muscle fiber area, although the respective nerve branches run parallel across this area. The long parallel-fibered sartorius muscle has a wider nerve tree and exhibits the same phenomenon for close parallel nerve branches, but end-plate bands along parallel nerve branches far apart cover the same muscle fiber area. The end-plate distribution in the bipennate, short-fibered gastrocnemius is zonal throughout the muscle except in certain compartments containing tonic fibers. The end-plate zone centers around the inner aponeurosis about half-way between the muscle tendon junctions of the fibers and is visible only at the muscle surface where muscle fibers run over their entire length at that surface. The results are of general use in the electrophysiology of neuromuscular transmission because they illustrate how in certain twitch muscles neuromuscular morphology may help to localize end-plates.

Notes: When a larva of Haplothrips verbasci is ready to feed, it grasps the surface of the leaf with its pretarsi, sinks down between its front legs, lifts its head, and places the tip of its mouthcone against the surface. It then shortens its mouthcone and punches a hole in the epidermis by rapidly and repeatedly protracting and retracting its left mandibular stylet. The thrips then inserts its two maxillary stylets as a unit into the wound with a series of rapid thrusts and withdrawals, salivating continuously while doing so. When a food source in the epidermis or mesophyll is found, probing and salivation stop and cibarial pumping begins. Cytoplasm is sucked into the opening at the tip of the protracted stylets, up the food canal between them and into the cibarium.Probing and feeding can occur without mandibular intervention but uptake of liquid seems to require use of the mutually coadapted maxillary stylets, even when these are fully retracted.Prior to molting, the larva protracts its maxillary stylets maximally and, in the pharate state, seems incapable of feeding or drinking.Structures used in feeding are fully described and are shown to resemble those of Hemiptera except for the presence of maxillary and labial palpi and the absence of the loral lobes, right mandible and of a salivary canal between the protracted maxillary stylets. Seven single and 18 paired muscles function in the feeding act, nine less than in adults of the same species.Differences in the feeding mechanism of terebrantian and tubuliferous thrips are discussed and evidence is presented to suggest that the simplified and more highly specialized mouthparts of the latter insects are adaptations for feeding in confining spaces.

Notes: In contemporary entomology the morphological characters of insects are not always treated according to their phylogenetic rank. Fossil evidence often gives clues for different interpretations. All primitive Paleozoic pterygote nymphs are now known to have had articulated, freely movable wings reinforced by tubular veins. This suggests that the wings of early Pterygota were engaged in flapping movements, that the immobilized, fixed, veinless wing pads of Recent nymphs have resulted from a later adaptation affecting only juveniles, and that the paranotal theory of wing origin is not valid. The wings of Paleozoic nymphs were curved backwards in Paleoptera and were flexed backwards at will in Neoptera, in both to reduce resistance during forward movement. Therefore, the fixed oblique-backwards position of wing pads in all modern nymphs is secondary and is not homologous in Paleoptera and Neoptera. Primitive Paleozoic nymphs had articulated and movable prothoracic wings which became in some modern insects transformed into prothoracic lobes and shields. The nine pairs of abdominal gillplates of Paleozoic mayfly nymphs have a venation pattern, position, and development comparable to that in thoracic wings, to which they are serially homologous. Vestigial equivalents of wings and legs were present in the abdomen of all primitive Paleoptera and primitive Neoptera. The ontogenetic development of Paleozoic nymphs was confluent, with many nymphal and subimaginal instars, and the metamorphic instar was missing. The metamorphic instar originated by the merging together of several instars of old nymphs; it occurred in most orders only after the Paleozoic, separately and in parallel in all modern major lineages (at least twice in Paleoptera, in Ephemeroptera and Odonata; separately in hemipteroid, blattoid, orthopteroid, and plecopteroid lineages of exopterygote Neoptera; and once only in Endopterygota). Endopterygota evolved from ametabolous, not from hemimetabolous, exopterygote Neoptera.The full primitive wing venation consists of six symmetrical pairs of veins; in each pair, the first branch is always convex and the second always concave; therefore costa, subcosta, radius, media, cubitus, and anal are all primitively composed of two separate branches. Each pair arises from a single veinal base formed from a sclerotized blood sinus. In the most primitive wings the circulatory system was as follows: the costa did not encircle the wing, the axillary cord was missing, and the blood pulsed in and out of each of the six primary, convex-concave vein pair systems through the six basal blood sinuses. This type of circulation is found as an archaic feature in modern mayflies. Wing corrugation first appeared in preflight wings, and hence is considered primitive for early (paleopterous) Pterygota. Somewhat leveled corrugation of the central wing veins is primitive for Neoptera. Leveled corrugation in some modern Ephemeroptera, as well as accentuated corrugation in higher Neoptera, are both derived characters. The wing tracheation of Recent Ephemeroptera is not fully homologous to that of other insects and represents a more primitive, segmental stage of tracheal system.Morphology of an ancient articular region in Palaeodictyoptera shows that the primitive pterygote wing hinge in its simplest form was straight and composed of two separate but adjoining morphological units: the tergal, formed by the tegula and axillaries; and the alar, formed by six sclerotized blood sinuses, the basivenales. The tergal sclerites were derived from the tergum as follows: the lateral part of the tergum became incised into five lobes; the prealare, suralare, median lobe, postmedian lobe and posterior notal wing process. From the tips of these lobes, five slanted tergal sclerites separated along the deep paranotal sulcus: the tegula, first axillary, second axillary, median sclerite, and third axillary. Primitively, all pteralia were arranged in two parallel series on both sides of the hinge. In Paleoptera, the series stayed more or less straight; in Neoptera, the series became V-shaped. Pteralia in Paleoptera and Neoptera have been homologized on the basis of the fossil record.A differential diagnosis between Paleoptera and Neoptera is given. Fossil evidence indicates that the major steps in evolution, which led to the origin first of Pterygota, then of Neoptera and Endopterygota, were triggered by the origin and the diversification of flight apparatus. It is believed here that all above mentioned major events in pterygote evolution occurred first in the immature stages.

Notes: Studies of the response of adult mammalian and amphibian ventricle to injury have indicated the formation of a connective tissue scar in the place of the wounded or amputated muscle. It has been demonstrated that amphibian myocytes adjacent to a wound surface, unlike mammalian myocytes, have a proliferative capacity. In the present study, a minced cardiac muscle graft was placed into the adult newt ventricle in order to increase the number of myocytes near a wound surface. With such an increased number of reactive myocytes, it was thought a new wall consisting primarily of muscle might be formed. One-sixteenth to one-eighth of the ventricular apex was removed, minced and returned to the amputation surface of the ventricle. General histological and autoradiographic studies were conducted on two sham-operated animals and on five experimental animals which were killed at 5, 10, 20, 30, 50 and 70 days after surgery. Major events of the repair and reorganization of minced cardiac muscle included blood clot formation followed by necrosis of the blood clot and much of the muscle graft. By ten days, an apparent coalescence of muscle fragments and continuity of ventricular and graft lumina were observed, although the graft area never formed an integrated unit with the wounded ventricular wall. The peak of mitotic activity (3.19%) and thymidine labeling (28.1%) of graft cells, including many cells which resembled cardiac myocytes, was observed at 20 days. At 30 days, the graft was observed as a continuous wall composed primarily of muscle fibers. Several 30-, 50- and 70-day grafts had rhythmic contractions. These results suggest that amphibian cardiac muscle has histogenetic and proliferative capacities not attributable to mammalian cardiac muscle.

Notes: An ultrastructural comparison of mouse oocytes isolated at various stages of growth and meiotic competence has been carried out. Progressive changes in the nucleoli, ribosomes, mitochondria, endoplasmic reticulum, Golgi complex, and other organelles and inclusions of the oocyte have been examined as a function of oocyte size by transmission electron microscopy. The observations presented support the idea that growth of the mammalian oocyte involves not just tremendous enlargement of the cell, but extensive alterations in its overall metabolism as reflected in the ultrastructure of the oocyte at various stages of growth.

Notes: The mammalian ovary has been studied by optical microscopy and by scanning and transmission electron microscopy with the purpose of presenting an integrated view of the differentiating mammalian follicle. During follicular development, changes in the granulosa cells are particularly noteworthy and include dramatic modifications in cell shape coincident with antrum formation. The cytoplasmic processes of those granulosa cells immediately surrounding the oocyte, as well as the more peripheral granulosa cells comprising a second and third layer, traverse the zona pellucida, infrequently interdigitate with the microvilli of the egg, and make both desmosomal and gap junction contacts with the oocyte. The zona pellucida is thus distinguished by numerous fenestrations of varying diameters. The membrana limitans (basal lamina) is a bipartite structure composed of (a) a homogeneous stratum upon which the peripheral layer of granulosa cells rests, and (b) an outer region of collagen-like fibers. The specific advantages and limitations of the different methodologies utilized to study folliculo-genesis are discussed.

Notes: The gross external morphology of the salivary glands of Gromphadorhina portentosa is described from light, scanning, and transmission electron microscopic observations. Various techniques, such as cryofracturing and epoxy-fracturing followed by plastic removal, were employed. Internally, the transportation system is characterized by a cuticle-lined lumen bordered by duct cells. The duct collects secretory products, some of which are reabsorbed by duct cells. Products are transported to intercalary ducts and eventually to the hypopharynx and/or salivary reservoirs. Transmission electron micrographs demonstrate distinctive morphological differences between duct cells bordering ductules and those which line expanded regions of the duct. Duct cells which surround ductules have a microvillous-lined apical border in which the cuticular coat of the lumen may be only partially developed. Duct cells in other regions may retain microvilli, or the apical plasma membrane may invaginate and vesiculate. In some cells the apical region has neither microvilli nor invaginations, but possesses two morphologically different forms of microtubules. Some duct cells are characterized by the presence of lamellar bodies in the nuclear region and/or collagenous material above the basal lamina in the area where the acinar duct becomes confluent with the intercalary duct. The plasma membranes between adjacent duct cells within acini become convoluted, forming loops filled with cytoplasm. These loops, along with contact and septate desmosomes formed between membranes, may serve dual functions: adherent mechanisms between cells and/or transportation of materials between cells.

Notes: Fertilization in Notophthalmus viridescens is internal and involves passage of the sperm through five layers of egg jelly (J5-J1, from outermost to innermost), each of which is secreted by a discrete region of the oviduct. Polyspermy is normal. Passage of the sperm through the jelly and into the egg was studied by a technique of artificial insemination similar to natural insemination, in that undiluted fluid from the vas deferens was applied directly to eggs with various layers of jelly present, followed by flooding with water three to five minutes later. In general, successful fertilization increased as the number of jelly layers increased; jellyless coelomic eggs were not fertilizable. Sperm passage through the jelly and into the egg usually occurs within one to three minutes. Upon hydration of the jelly, barriers to sperm penetration develop in layers J5 and J3. Changes in the egg jelly thus seem to be involved in the restriction of polyspermy to a low level.

Notes: A review of the literature of the gastric glands of reptiles shows marked differences of opinion concerning the nature and character of the cells composing the gastric glands.The present investigation of the gastric glands of the alligator has been carried out by histochemical and physiological experiments, rather than by the usual morphological methods, but the results can be stated both in terms of structure and function.1The surface epithelial cells and those lining the gland pits in the fundic, cardiac, and pyloric regions of the stomach of the alligator are not strictly comparable functionally to the mucous cells of mammals.2The cells composing the necks and bodies of the glands in the fundus, according to histochemical reactions, are parietal cells.3Certain cells lying beneath the columnar epithelial cells lining the lumen of the stomach and the foveolae react to one method of fixation and staining as do the chief cells of mammalian material.4The results of the experiment with the vital dye, neutral red, show that the cells of the gastric pits, the necks and bodies of the glands in the fundus of the alligator's stomach, react identically as those of the mammalian stomach.5The gastric juice of the alligator is acid to litmus-paper and contains a free mineral acid.

Notes: The course of digestion of an essentially protein food (beef liver) was followed by histological and histochemical methods in Planaria dorotocephala. After an average fasting period of two weeks, the planarians were fed and examined at close time intervals, ranging from one minute to eighty-seven days after feeding. Liver particles are engulfed by the phagocytic cells of the intestine into food vacuoles, where a series of digestive changes occur. The liver particles coalesce into a granular spherule which gradually condenses into a homogeneous and chromatophilic spherule. As the spherule transforms from a granular to a homogeneous condition, it exhibits a gradually increasing affinity for stains, an intensified protein reaction, and a gradual diminution in size. These spherules are protein, since they give positive xanthoproteic and Millon reactions.The homogeneous protein spherules gradually disappear, beginning at about twelve hours after feeding and continuing until the fifth day. During this period fat-droplets form, gradually increasing at the expense of the protein spherules. The protein spherules apparently dissolve into the cytoplasm, furnishing intermediate chemical compounds (tests indicate that a carbohydrate stage does not intervene) from which fat is synthesized. It thus appears that the fat is formed from the protein spherules. The fat thus formed is stored in the phagocytic cells, and remains unchanged in quantity for a fasting period lasting six weeks, after which it gradually diminishes. During the engulfment of the food, the fat decreases markedly, apparently furnishing energy for phagocytic activities. A few of the protein spherules may persist as «protein reserve».

Notes: Microscopic examination of both living and stained forms indicates that the so-called ‘multivacuolate’ and ‘amicronucleate races of Paramecium caudatum’ belong to the species Paramecium multimicronucleata. The published accounts of the morphology and cultural characteristics of the various forms are compared and provide additional evidence. A more complete description is given, including distinctive characters previously omitted.The conjugation process of P. multimicronucleata in general resembles that of P. caudatum, most of the differences being due to the presence of four micronuclei instead of one. These each divide twice with characteristic figures, twelve of the sixteen daughter nuclei then degenerating. One of the remaining four splits to form a single pair of functional pronuclei in each cell. The two migratory pronuclei interchange as in P. caudatum. The synkaryon divides three times, and probably seven of these nuclei degenerate. The remaining one apparently undergoes two divisions. In most cases by six to eight hours after the conjugants separate two micronuclei of the four thus produced form enlarged macronuclear anlagen, the other two remaining as micronuclei. Each anlage divides within the next two or four hours, producing four macronuclear and four micronuclear analagen. Two fissions, each preceded by a division of the micronuclei, restore vegetative conditions.The process described above is compared with conjugation in P. bursaria, P. caudatum, and P. putrinum.

Notes: Systems of fiber-like structures traverse ciliated cells and epithelia in a way to suggest conduction paths for stimuli for coordinating and regulating ciliary movement, and results of microdissection support such an interpretation.Some fibers of the systems in epithelia of the gill terminate on the nuclear membrane, some between nuclei in the basal cytoplasm.The observed double refringency of the fibrillar apparatus places it in the category of irritable and contractile substance.Bipolar cells and nerve-like fibers lie immediately below and parallel with ciliated epithelia of the gill, but direct connections of these fibers with the intracellular system, although suspected, was not demonstrated.Ciliated epithelia of the gill are syncytial in character in the direction of the beat of cilia.Interciliary structures occur in the cuticular portion of ciliated epithelia which are interpreted to function in taking up strains in the gelled cytoplasm caused by the beat of cilia.Cilia occur in pairs in epithelia of the gill, and members of pairs are fused at their distal ends.Each cilium, as seen in dark-field illumination, pierces its basal body, and the fiber that is a continuation of the cilium divides immediately below the basal body into two; one diverging to the right, one to the left.Each cilium is composed of many delicate fibrillae.

Notes: The sperm of the shiner surfperch are packaged into high density aggregations which are introduced into the female genital tract at insemination. Germ cell differentiation occurs within cysts formed by nongerminal Sertoli cells. In late spermiogenesis, spermatozoa within the cysts come to lie parallel to each other and become more densely packed. These sperm packets (spermatophores), containing approximately 600 spermatozoa, then are released into the efferent sperm ducts.The exact nature of the spermatophore binding material is not known, but a major component is proteinaceous and is synthesized in the rough endoplasmic reticulum of the efferent sperm duct epithelial cells. The mechanism by which the spermatophores pass from cysts into ducts is not clear. It appears that whereas many Sertoli cells degenerate causing the cyst wall to break down, many Sertoli cells do not degenerate, but rather assume the configuration of columnar duct cells. The spermatophores remain intact within the testicular ducts, but rapidly dissolve within the female ducts in response to increased pH.

Notes: The telemetered electromyographic activity (EMG) of select hindlimb muscles of unrestrained cats during standing, walking, trotting, and galloping have been recorded. Simultaneous cinematographic records permitted close correlation of muscle activity and locomotor behavior. In general, the pattern of extensor activity of the ankle, knee, and hip during locomotion is fairly consistent, while that of the flexors is more variable.Changes in basic EMG patterns from walk, to trot, to gallop are most evident in the two-jointed muscles associated with the knee and hip. Progressively greater variation of activity onset and cessation can be seen among extensor muscle groups from the walk, to trot, to gallop. Co-activation of the joint extensors and flexors, especially of the hip, at the end of the stance phase (E3) is slight in the walk, moderate in the trot, and considerable in the gallop. These EMG changes are necessary to meet the demands imposed upon the musculature at the faster gaits, particularly galloping, which include limb rigidity as related to loading, momentum as related to the limb's directional change from the stance phase to the swing phase, and lower spinal movements.The peroneal muscles of the ankle and the gluteal muscles of the hip show extensor activity and act as joint stabilizers during locomotion. Both biceps femoris anterior muscle and biceps femoris posterior muscle show consistent hip extensor patterns at all gaits. During quiet standing, extensor activity about the knee, ankle, and metatarsophalangeal joints is evident; but the hip extensor and flexor musculature is remarkably silent.EMG data for unrestrained cats are compared to those of dogs on a treadmill (Tokuriki, '73a,b, '74; Wentink, '76) and those recorded from decerebrate cats (mesencephalic preparation) during controlled locomotion (Gambaryan et al., '71). The EMG patterns from decerebrate cats are more consistent at the walk and gallop within functional groups of muscles at the ankle, knee, and hip than the EMG patterns observed in unrestrained cats or animals moving on a treadmill.

Notes: The relationship of the cells and tissues which comprise the developing ovarian follicle in Xenopus laevis has been studied with scanning and transmission electron microscopy. The saclike ovary is covered on its coelomic side by a squamous epithelium. The cells of this epithelium are extensively interdigitated, and each bears a short, centrally positioned cilium. The lumenal surface of the ovary is covered with a layer of nonciliated squamous cells. The areas of cell-cell contact are characterized by desmosomes in both epithelia, and between the epithelia lies a connective tissue layer-the theca-which contains collagen fibers, blood vessels, nerves, smooth muscle cells and oogonia. Beneath the theca in each follicle lies a single layer of flat stellate follicle cells. Associations between adjacent follicle cells are intermittent, leaving wide spaces or channels. Junctional contacts between neighboring follicle cells are characterized by desmosomes. From the basal surface of each follicle cell extend long, broad macrovilli which penetrate the underlying acellular vitelline envelope and contact the surface of the oocyte. Evidence is presented which suggests that follicle cells may produce and release components which participate in the formation of the vitelline envelope which consists of a 3-dimensional lattice of ropey fibers. Passageways through the vitelline envelope allow the maintenance of contact between oocyte and follicle cells and also allow ready penetration of materials both to the oocyte (e.g., vitellogenin) and from it (e.g., cortical granule material) at different stages of its development.

Notes: This study reveals age related changes in the microscopic structure of the paired frontal bone of the domestic rabbit. Undecalcified ground sections were prepared from anterior frontal bone slices removed from New Zealand White rabbits ranging from birth to 24 months of age. Included were 40 females, 4 males and 6 rabbits less than 14 days old of unknown sex. The ground sections revealed both qualitative and quantitative age changes. Qualitative changes include change in bone tissue types and developmental processes, and presence or absence of primary and secondary osteones. Quantitative changes were measured by counting primary osteones in the outer table of each frontal bone half within 1.6 mm of the metopic suture. In this region, primary osteones were absent at birth, limited in number at 14 days and generally numerous between one and three months of age. In animals older than three months, numbers of primary osteones generally decreased with increasing age. No animals older than 16 months revealed primary osteones. Possible sources of variability in the relationship between observed primary osteone number and age include ability to recognize primary osteones, methods of sampling and processing bone slices, sex related differences and diseases afflicting specimen. Significance of this study includes increased knowledge of frontal bone growth and histology.

Notes: Light microscopic autoradiography with 3H-thymidine demonstrates that the three regions of the alimentary tract in the larval (ammocoete) lamprey, Petromyzon marinus L., possess different patterns for renewing their epithelium. In the oesophagus, columnar and mucous cells originate from stem cells located at the bases of folds and migrate to the tops of the folds where they are apparently extruded. Ciliated cells, located only at the tops of the folds, seem to differentiate from migrating columnar cells. In the anterior intestine, stem cells are present throughout the epithelium so that there is limited migration of cells and their extrusion occurs randomly. In the posterior intestine, the stem cells located at the bases of the typhlosole provide a continuous population that differentiates and migrates to the top of the typhlosole and to the opposite epithelial wall where they are presumably extruded. The rates of cell renewal in all three epithelial regions of the alimentary tract are slower in animals maintained at 10 ± 1°C compared with those kept at 21 ± 1°C. Comparatively, ammocoetes have the least specialized system for cell renewal known in the alimentary tract of a vertebrate.

Notes: The renal sac of the ascidian family Molgulidae (Tunicata, phylum Chordata) has been thought to function as a kidney, yet its structure, contents and activities seem incompatible with current generalizations regarding excretory processes in marine animals. The development of the renal sac is described here as part of a general effort to reexamine the organ's role in Molgula manhattensis. Light microscopy of living animals and fixed material has shown the following: (1) The renal sac begins to sequester concretions before the heart starts beating and before feeding begins. Therefore, blood circulation by heartbeat is not necessary for production or transport of the initial concretions, whatever its effects may be on the renal sac in older individuals. Ingested food cannot provide the initial concretion material. (2) In laboratory-raised animals, concretions appear in the renal sac before “renal sac organisms” (fungus-like organisms seen in the renal sac of all field-collected adults) can be detected. Thus, at least some portion of the concretions can be produced by Molgula in the absence of renal sac organisms. (3) No openings have been detected in the renal sac at any stage of its development, nor is there any evidence that concretions are dissolved or transported out of the renal sac. (4) The development and morphology of the renal sac are consistent with the hypothesis that the organ is an epicardial derivative, except that the renal sac arises from post-pharyngeal (presumptive gut) endoderm, rather than pharyngeal endoderm.

Notes: Oocytes and nurse tissue of Bruchidius differentiate from germ cells during the extended period of pupal development (7.2 ± 0.6 days). A system of 15 pupal stages correlates ovarian development with changes in pigmentation of the eyes, maxillae, alae and tarsalia. The ovarioles grow in length at a constant rate, though their width does not change.A differentiating zone, consisting of germ cells and the basal layer of interstitial cells, arises at the base of the tropharium and separates presumptive oocytes and nurse cells. Early in pupal development the germ cells are arranged in primary syncytia with the cells connected by persisting intercellular bridges filled with fusomal material, never with larger particles, such as mitochondria. At later stages membrane disintegration changes the primary syncytium into a secondary one including all nurse cell nuclei.Nutritive cords are first noticeable when differentiation of oocytes and nurse cells starts. The cords seem to be of primary origin, i.e., they are connections between sister cells which become elongated as these cells are separated during growth. This is indicated by the persistence of intercellular bridges which are sometimes found as part of the membrane of growing nutritive cords connecting young oocytes with the nurse cell syncytium.

Notes: The formation of protein-carbohydrate yolk in the statoblast of a fresh-water bryozoan, Pectinatella gelatinosa, was studied by electron microscopy. Two types (I and II) of yolk cells were distinguished. The type I yolk cells are mononucleate and comprise a large majority of the yolk cells. The type II yolk cells are small in number; they become multinucleate by fusion of cells at an early stage of vitellogenesis. In both types of yolk cells, electron-dense granules (dense bodies) are formed in Golgi or condensing vacuoles, which are then called yolk granules. For the formation of yolk granules, the following processes are considered: 1. Yolk protein is synthesized in the rough-surfaced endoplasmic reticulum (RER) of the yolk cells. 2. The synthesized protein condenses in the cisternal space of the RER and is packaged into small oval swellings, which are then released from the RER as small vesicles (Golgi vesicles, 300-600 A in diameter). 3. The small vesicles fuse with one another to form condensing vacuoles, or with pre-existing growing yolk granules. 4. In the matrix of the condensing vacuoles or growing yolk granules, electron-dense fibers are fabricated and then arranged in a paracrystalline pattern to form the dense body. 5. After the dense body reaches its full size, excess membrane is removed and eventually the yolk granules come to mature. Toward the end of vitellogenesis of the yolk cells, the cytoplasmic organelles are ingested by autophagosomes derived from multivesicular bodies and disappear.

Notes: Testis structure in four species of goodeid teleosts is described. Testicular tubules terminate blindly at the testis periphery where spermatogonia are located. In goodeid teleosts, development of sperm takes place synchronously within cysts whose periphery is made up of a single layer of Sertoli cells. Upon completion of spermiogenesis, spermiation ensues wherein sperm are shed, as spermatozeugmata, into the testis efferent duct system. Subsequently, Sertoli cells, which comprised the cyst periphery, transform into efferent duct cells.Sertoli cells phagocytize residual bodies and are involved in the formation of spermatozeugmata. The structure of the goodeid spermatozeugmatum is quite different from that observed in the related poeciliids. It is concluded, in view of this and other considerations, that the goodeids and poeciliids have independently evolved solutions to the problems of internal fertilization and gestation.

Notes: The papillae basilares of 12 species of lizards from seven different families were studied by SEM. The iguanids, Sceloporus magister and S. occidentalis, have typical “iguanid type” papillae with central short-ciliated unidirectional hair cell segments and apical and basal long-ciliated bidirectional hair cell segments. These species of Sceloporus are unique among iguanids in that the bidirectional segments consist of but two rows of hair cells. The agamids, Agama agama and Calotes nigrolabius, have an “agamid-anguid type” papilla consisting of an apical short-ciliated unidirectional hair cell segment and a longer basal bidirectional segment. Agama agama is unusual in having a few long-ciliated hair cells at the apical end of the apical short-ciliated segment. The agamid, Uromastix sp., has an “iguanid type” papilla with a central short-ciliated unidirectional segment and apical and basal bidirectional segments. The anguid, Ophisaurus ventralis, has an “iguanid” papillar pattern with the short-ciliated segment centrally located. All the short-ciliated hair cells of the above species are covered by a limbus-attached tectorial network or cap and the long-ciliated hair cells, only by loose tectorial strands.The lacertids, Lacerta viridis and L. galloti, have papillae divided into two separate segments. The shorter apical segment consists of opposingly oriented, widely separated short-ciliated cells covered by a heavy tectorial membrane. The apical portion of the longer basal segment consists of unidirectionally oriented hair cells, while the greater part of the segment has opposingly oriented hair cells.The xantusiids, Xantusia vigilis and X. henshawi, have papillae made up of separate small apical segments and elongated basal segments. The apical hair cells are largely, but not exclusively, unidirectional and are covered by a heavy tectorial cap. The basal strip is bidirectional and the hair cells are covered by sallets. The kinocilial heads are arrowhead-shaped.The papilla of the cordylid, Cordylus jonesii, is very similar to that of Xantusia except that the apical segment is not completely separated from the basal strip.The papilla of the Varanus bengalensis is divided into a shorter apical and a longer basal segment. The hair cells of the entire apical and the basal three quarters of the basal segment are opposingly oriented, not with reference to the midpapillary axis but randomly to either the neural or abneural direction. The apical quarter of the basal segment contains unidirectional, abneurally oriented hair cells. The entire papilla is covered by a dense tectorial membrane.The functional correlations of the above structural variables are discussed.

Notes: The circulatory systems of four polystyelids, Botryllus schlosseri, B. primigenus, Botrylloides violaceus and Symplegma reptans, were compared. The palleal buds are connected to the parent zooid by a peduncle and to the colonial vascular system by connecting vessels. The peduncle of S. reptans disappears at an earlier stage of bud development than in B. primigenus; it survives the dissolution of the parent zooid in B. schlosseri and B. violaceus. The connecting vessel is formed by anastomosis between an epidermal outgrowth from the bud and a neighboring colonial vessel, and is characterized by the presence of a sphincter. The number of connecting vessels formed in a palleal bud is three in S. reptans, two in B. primigenus and one each in B. schlosseri and B. violaceus. In each species, the larva has eight rudiments of ampullae. In B. primigenus, the original ampullae degenerate soon after metamorphosis and new ampullae extend from the ventral epidermis of the oozooid. In the other species, the colonial vascular system is derived from the original ampullae.The whole colonial vascular system contracts and expands periodically, with regionally different phases. During each expansion cycle, the sphincter contracts once in B. primigenus and twice in S. reptans. The correlation may be due to blood pressure and the propagation of excitation through the colonial vascular system.

Notes: Scale neogenesis following excision of pieces of skin of various sizes and shapes has been studied in several squamate species. In small wounds, neogenesis does not occur, the wound region contracts, and increased areas of hinge differentiation are seen. In large wounds, the time taken for neogenesis to occur, and the size, shape, distribution, and number of the reformed units, are variable. We confirm previous reports that neogenesis accompanies a renewal phase of the shedding cycle, and suggests that this is because both types of morphogenesis require germinal stability.All types of trauma thus far studied show the initial formation of a hyperplastic wound epithelium with the histological characteristics of a normal α-layer: such tissues are the basis for physiological barrier functions. The mechanical functions of the skin can be fairly adequately restored even by abnormal neogenic scales. The observed variability in the process of scale neogenesis, and the final form of the individual units, are argued to be the result of mechanical factors impinging on the differentiating tissues.

Notes: The stages in wound healing of the wax-moth, Galleria mellonella, were examined using routine histological techniques. Final instar larvae were wounded and maintained for up to 72 hours before fixation, dehydration and embedding in Paraplast wax or Araldite.Immediately after wounding both fat-body and hemolymph were forced through the wound to form a plug. Concomitantly, the hemolymph coagulated forming vast networks of strand-like material attached to the hemocytes underlying the wound. After one to two hours this plug melanized and the cells became highly necrotic. Six hours after wounding, there was a massive influx of hemocytes which eventually attached to the melanized layer over the wound to form a multicellular sheath. Twelve to twenty-four hours later, the epidermal cells underlying the broken cuticle detached and migrated across the wound to form a new intact layer. This layer secreted an amorphous material which is probably the precursor of the new cuticle. Hemocyte functions during wound healing and other cellular defenses are discussed.

Notes: Time-lapse cinemicrography was used to show what changes in the number, size, shape, arrangement and what movements of apices of superficial cells occur during epiboly, extension, convergence and blastopore formation in the blastula or gastrula of Xenopus laevis. Epiboly of the animal region occurs by apical expansion of superficial cells at a nearly constant rate from the midblastula to the midgastrula stage. Egression of deep cells into the superficial layer does not occur. Extension of the dorsal marginal zone begins in the late blastula stage with the rapid spreading of the apices of cells in this region and this continues until the onset of neurulation when rapid shrinkage begins. Extension and convergence of the dorsal marginal zone occurs by a rearrangement in which individual cells exchange neighbors and by a change in the shape of the cell apices. Regional differences in apical expansion are accompanied by differences in rate of anticlinal division of superficial cells such that cells in all sectors of the animal region and the marginal zone show similar patterns of decrease in apparent apical area. Shrinkage of the apices of bottle cells during blastopore formation is described. From this and other studies, a model of the cellular behavior of epiboly, extension and convergence is constructed and several hypotheses as to how these activities might generate the mechanical forces of the gastrulation movements are presented.

Notes: The digestive tract of Hoplosternum thoracatum consists of an esophagus, gastric area, anterior digestive intestine with elaborate folds, digestive intestine with decreasing folds and thin, smooth-surfaced respiratory intestine. The upper tract has a mucoid columnar lining which is gently folded, whereas the gastric area has numerous pits opening into the tubular secretory glands. Striated muscle comprises the anterior muscularis but is replaced by inner circular and outer longitudinal smooth muscle layers in the gastric region. The digestive intestinal mucosa is elaborately folded, consisting of columnar cells with prominent brush borders. Mucosa, submucosa, circular and longitudinal muscularis and serosa layers are present throughout the tract. Goblet cells occur in both the digestive and respiratory intestine. Major changes that appear in the respiratory intestine are a drastic reduction in mucosa epithelial thickness and the penetration of an elaborate capillary bed into the epithelium. The other basic layers are not significantly reduced in thickness. The air-blood barrier consists of the thin epithelium, basement lamina and very thin capillary endothelium. Regional cellular composition and ultrastructural features are correlated with respective digestive and respiratory functions.

Notes: The morphology and microscopic anatomy of the reproductive organs and colliculus seminalis of the male rabbit are described and illustrated. Special attention is given to the accessory sex glands, because not all have been accurately identified previously. The terminology suggested for the accessory glands (with other terms commonly used in the literature in parentheses) follows: glandula vesicularis (glandula seminalis, vesicula seminalis), proprostata (glandula vesicularis, coagulating gland, prostata), prostata, paraprostata (glandula Cowperi superior), glandula bulbourethralis (glandula Cowperi inferior). The English equivalents are vesicular, proprostate, prostate, paraprostate and bulbourethral glands. Organs were obtained from 39 adult Dutch-belted rabbits that averaged 2,023 g in bodyweight. Organ weights (means and standard deviations) were as follows: testis, 2.035 ± 0.529 g; caput epididymidis, 0.264 ± 0.087 g; corpus epididymidis, 0.046 ± 0.019 g; cauda epididymidis, 0.398 ± 0.123 g; proximal part of the ductus deferens, 0.098 ± 0.026 g; ampulla of the ductus deferens, 0.177 ± 0.069 g; vesicular gland, 0.529 ± 1.169 g; proprostate gland, 0.633 ± 0.304 g; prostate gland, 0.411 ± 0.181 g; paraprostate gland, 0.040 ± 0.019 g; bulbourethral gland, 0.390 ± 0.133 g; and epididymal fat pad, 0.545 ± 0.339 g. Correlations among organ weights were calculated and interrelationships among them and bodyweight are discussed.

Notes: Early embryonic mitosis of the silkworm, Bombyx mori, was morphologically studied in the normal eggs and in the eggs treated by low temperature (-10°C).The first embryonic mitosis is observed in the eggs at 120 to 150 minutes after deposition at 26°C. After egg and sperm pronuclei unite, a spindle is formed in each of the pronuclei independently. At metaphase and anaphase paternal and maternal chromosomes are in separate groups on a spindle (gonomeric) and karyogamy takes place at telophase when they reach the poles.The second embryonic mitosis is shown in the eggs at 180 to 210 minutes after deposition. The division of two nuclei is not synchronous in the silkworm, and the mitosis is not gonomeric.In the eggs treated by low temperature, spindle fibers are not observed at all at -10°C, and chromosomes, which form two deeply stained masses of irregular shape, are seen in the less stained area of spindle shape. When the eggs are returned to 26°C, some eggs go into normal gonomeric division, while some form two small and compact spindles, which seem to be derived from each of the pronuclei. It was observed that these compact spindles are able to continue mitosis.

Notes: The development and cytology of cartilage and bone in the limbs from the fifty-second hour of incubation to the first day after hatching are described.The chief points of interest arising from this study are: (1) Chondroblasts when liberated during cartilage resorption die and disintegrate. (2) All the long bones possess structures which, though not undergoing independent ossification, are homologous with the mammalian epiphyses. (3) Endochondral ossification occurs only in the epiphyses and ends of the diaphyses. (4) The marrow cavity contains multinucleated giant cells which appear to be formed by the fusion of degenerating cells.

Notes: Hermaphroditic gonads of Rhabdites elegans can be distinguished in early developmental stages, but oogonia cannot be told from spermatogonia. Certain peculiar males show developmental processes approaching those of hermaphrodites. More eggs are produced by a hermaphrodite than there are sperm with which to fertilize them. Such exhausted hermaphrodites may be mated with males and produce fertile eggs, but convincing evidence of cross-fertilization is lacking. Unmated females of Diplogaster aerivora live longer than mated ones, but no difference was found in the males. Sexual instinct seems to be lacking in males of R. dolichura and R. elegans.Hermaphrodites mated with males produce many more male offspring than by self-fertilization, but these do not exhibit sexual instincts. Females produced by cross-fertilization are not pure females, nor have they been found at all in R. elegans or R. dolichura. After fertilization in these two species, both polar bodies are formed and the pronuclei fuse. Sex is determined by the form of sperm.

Notes: Total splenectomy in the frog means practically complete extirpation of the erythropoietic apparatus. Out of sixty-four operations it was followed by: 1Stimulation of erythropoiesis in the kidney (mesonephros), 35 to 46 per cent.2Stimulation of erythropoiesis in the fat-bodies, 5 per cent; lymphocytopoiesis, 8 per cent.3Stimulation of erythropoiesis in the bone-marrow, 11 per cent.4Formation of a new spleen, 8 per cent.5No perceptible erythropoletic stimulation, 24 per cent. The latter leads to a condition of anemia followed by death within about sixty days.Partial splenectomy leads to spleen regeneration.The life tenure of the frog erythrocyte is approximately 100 days.Total splenectomy experiments indicate that the chief function of the spleen in the frog inheres largely in its lymphocyte content and in the transformation of lymphocytes into erythrocytes.

Notes: This paper represents the third part of a monograph on the development of the lymphatics and lymph hearts of Anura. In this part are considered the origin and development of the subvertebral, lateral, and dorsal lymphatics of the trunk, the caudal lymphatics, and the posterior lymph hearts.The chief lymphatic trunks arise along the veins from a series of small, spindle-shaped, and discontinuous anlagen which subsequently coalesce and thus establish continuity with one another. Lymph plexuses are formed from which emerge the main secondary lymph channels. After such trunks are laid down as indicated, smaller branches and capillaries spring from them by sprouting or extension, due to their actively proliferating endothelium.The posterior lymph hearts ‘crystallize,’ so to speak, from localized areas of the lateral lymphatic plexus. During its reorganization and differentiation, it temporarily separates from the surrounding lymph plexus. Other genetic details, such as the formation of its valves, histogenesis of its walls, number of hearts laid down, etc., are also considered. Twenty-two figures (microphotographs and reconstructions) accompany the text.

Notes: In general, the changes of locomotor rate of Amoeba under the influence of temperature are similar to the effects of temperature in other biological processes.The rate increases with rising and decreases with falling temperatures within a certain temperature range, this being, for the forms investigated, the interval between 6° and 23.5°C. In some individuals, however, these limits were found to be wider, extending from 2° to 26°. There is an average optimum at about 23.5°, beyond which an increase in temperature is followed by a decrease in rate. The immediate response of Amoeba to a change of temperature is variable, due, as was shown in a previous paper, to the fact that locomotor-rate changes are rhythmic. The effect of a change of temperature is thus conditioned not only by the enviornmental factors, but also by the phases of the locomotor rhythm. This fact also makes it difficult to establish the exact quantitative relationship which exists between a change of temperature and the locomotor rate - an aspect which will be developed in a future paper.

Notes: The female reproductive system comprises the ovaries, oviducts, vagina, spermatheca, and spermathecal gland. No colleterial glands are present. The ovaries are paired and each is composed of about eighteen ovarian tubules terminating in a cup-shaped modification of the oviduct - the egg calyx. The epithelial lining of the oviduct is glandular. The spermatheca, a bladder-shaped sac situated dorsal to and between the two ovaries, opens into the vagina near the exterior and is filled with spermatozoa after copulation. Spermatozoa have not been found in any other part of the female. Dorsal to the spermatheca and lying against it is the spermathecal gland. It is connected with the spermatheca by an elongate spermathecal duct.The male reproductive system comprises the testes, vas deferens, accessory glands, and the penis. Each testis is composed of eight to ten cone-shaped follicles, which are composed of a number of cysts so arranged as to appear segmented. All of the cells of each cyst are in approximately the same stage of development. No seminal receptacle is present. Each follicle is connected with the vas deferens by an efferent tube. The paired vas deferens opens into the sac-like intromittant organ or penis. The terminal portion of the penis may be everted, and when everted is conical in shape. At its base is a thin chitinous collar, the margins of which are thickened, forming ridges.

Notes: A study of the peripheral nerves of the earthworm shows that one pair of nerve trunks arise from the lateral regions of the cerebral ganglion, one pair from near the lateral, and two pairs from the ventral region of the circumpharyngeal connectives. These supply, in the order given, the prostomium, segment 1 and segment 2. Segment 3 and each succeeding segment, except the last, are supplied with three pairs of nerve trunks which arise from the nerve cord in the segment concerned. None of the nerve trunks of the body was observed to send branches to more than one segment, which shows that they are segmental in origin and distribution.The anterior portion of the central nervous system has undergone caudal migration and modification of its ganglia. Some of the nerve trunks have disappeared through atrophy, while others have become fused at their bases.A subepidermal nerve plexus is found at the base of the epidermal cells from which nerve fibers pass to the internal nerve net and to the central nervous system. This plexus also sends intercellular and intracellular fibers into the epidermis.The so-called sense cells of the epidermis appear to be the cell bodies of sensory neurones which send nerve fibers to the ganglia of the central nervous system, where they form synaptic connections with other neurones.There is an enteric nerve plexus in the wall of the alimentary canal which is directly connected to the circumpharyngeal connectives.

Notes: Astylosternus robustus has greatly reduced lungs. All Amphibia exhibiting such a reduction have their epidermis either penetrated by capillaries or thinned to facilitate greater cutaneous respiration. The epidermis of both sexes of A. robustus is penetrated by capillaries. The «hairs» of the adult male are merely extensions of this vasculated epidermis to compensate for the greater muscularity, size, and activity of this sex.The digits of terrestrial urodeles do not serve as special centers of cutaneous respiration. Digital sinuses are present in all urodeles. The abdominal and femoral tubercles of arboreal and some terrestrial frogs may function greatly in respiration, for their epidermis is penetrated by capillaries.All urodeles and frogs having well-developed and frequently emptied lungs possess a functionally complete auricular septum and a spiral valve. Injection experiments demonstrate a complete separation of arterial and venous blood in living specimens. A reduction of the lungs conditions a reduction of the left auricle, but disuse causes no change in size. A great decrease of the lungs, or even a disuse of them, conditions a fenestration of the auricular septum and a loss of the spiral valve. The spiral valve is formed by a backward growth of one of the synangial valves and is not homologous with the accessory valves of dipnoans. Lungless salamanders have no left auricle and no spiral valve.

Notes: One of the most perfect “lock and key” adaptations known, the external reproductive organs in spiders are subject to considerable variations. Two extreme types of female reproductive organs are described in detail, and these in turn compared with the European species of the same genus. Thus it is shown that the reproductive system in the same genus of spiders may exhibit great differences in structure while all other characters remain more or less the same, the natural conclusion being that caution should be exercised in creating new or splitting up old genera on the basis of characters of the external reproductive system. The same applies to the male.Two extreme types of palpi are described and then compared with the palpi of the European species. In the case of the male, however, the differences seem to be of a less profound nature.

Notes: The shedding of epidermis in this species, as in most amphibia, is periodic. A single outer layer of cells separates nearly simultaneously over the whole body; two hours to ten days may be required for the process. In the first three months of laboratory existence the average frequency of molting was 9 per cent. In nature the frequency was only 2 per cent; this increased during the life in confinement in five months up to 25 per cent. Death in the laboratory was usually preceded by numerous molts.The time of a molt is not normally determined by any one of a number of ordinary external conditions which were modified; but nevertheless several means were found of inducing molting. These were, in order of their efficacy: bandaging with gauze on body or tail, wrapping the body with thread, stitching the body wall, applying hot water, and transplanting skin. Molting frequencies up to 98 per cent may thus be obtained.Since molting is periodic and simultaneous, it is evidently coordinated. Experimental induction requires a latent period of six to ninety-six hours, depending upon the stimulus. Recent skin grafts molt with the host, so that the coordination is probably chemical. The primary significance of molting in all groups of animals is possibly the getting rid of unautolyzable waste materials, i.e., worn epithelial structures.

Notes: The gross morphology of the nervous system supplying the dorsal longitudinal flight muscles of tsetse flies is described. Electron microscopical investigation of the nerves reveals that the dorsal longitudinal muscles are innervated by branches from four main axons. A detailed description of the neuromuscular junctions in the flight muscle is presented.

Notes: Melanin deposits in the heads of both true vipers (Viperinae) and pit vipers (Crotalinae) are concentrated over the dorsal and dorsolateral aspects of the venom glands. This pigment may occur in any or all of six sites which include the epidermis, dermis, tissues covering the venom glands, and the interior of the glands themselves. The extreme localization of these melanin deposits suggests that they shield the venom glands from light. Calculations indicate that without such shielding the light energy penetrating the venom glands in the visible and ultraviolet portions of the solar spectrum would damage the venom-synthesizing apparatus and detoxify stored venom.Elapid and hydrophiid snakes have less dense pigment over the venom gland than vipers. Literature reports indicate that elapid venom is less sensitive to photodetoxification than is venom from vipers. Most colubrid snakes, including several with protein-secreting Duvernoy's glands, have little or no melanin associated with the glands. Venomous colubrids in the genera Ahaetulla, Dryophis, Leptophis, and Oxybelis have pigment over the glands as dense as that seen in vipers.Iridophores probably also shield venom glands from radiation. In puff adders and Gaboon vipers (Bitis) there appears to be an ontogenetic change in the shielding of the venom glands from melanocytes in young individuals to iridophores in adults.