ALBERT

Notes: Development of the secondary palate in Swiss white mouse embroyos was studied from age nine-and-one-half days in utero to the stage of mesenchymal coalescence in the secondary palate (approximately fifteen-and-one-half days). The greatest changes observed occur in the mesenchyme. At early stages, mesenchymal cells underlying oral ectoderm of the head are few and only occasionally contact the ectoderm. Electron micrographs show large intercellular spaces between the ectodermal cells. As embryogenesis continues, the mesenchymal cells become more numerous, closer to each other and closer to the epithelium. Just prior to horizontal transposition of shelves, the mesenchymal cells spread farther from each other and from the palatal epithelium and epithelium of the palatal tip becomes stretched. Ultrastructurally the intercellular spaces between epithelial cells of the palate tip have become much smaller. Some mitochondria in some epithelial cells are swollen and have clear matrices and distorted cristae. The shelves become horizontal and meet in the midpalate. Cells with degeneration bodies are seen in the epithelial seam. The seam undergoes autolysis and is replaced by mesenchyme. The morphological changes described, particularly in the mesenchyme, may play an important role in determining the effect of various teratogens at different stages of palatal development. The changes in both mesenchyme and epithelial cells in the later stages may constitute part of the process of preparing shelves for fusion as postulated by Pourtois ('66).

Notes: It has been shown that the external parameters of eggs of the garden lizard, Calotes versicolor, are not suitable for assessing the exact developmental stages of embryos. In order to make use of this lizard's embryos for experimental work, a series of developmental stages has been characterized, using various morphological features.

Notes: The integument and podia of the sea cucumber Thyone briareus were examined by bright field and electron microscopy. The epidermal surface was found to be covered by an acellular, PAS positive cuticle which appeared to be secreted by the underlying epidermal cells. Although the superficial portion of the cuticle contains numerous fine filaments, their ultrastructure bears no resemblance to collagen fibers. The epidermal cells are widely spaced and have long apical processes that extend along the under surface of the cuticle forming a contiguous epithelium. The apical expansions of the epidermal cells are attached to one another by means of septate desmosomes which may run continuously around all epidermal cells. Special attachment structures within these apical expansions appear to bind the cuticle to the dermis. The epidermal cells and their apical expansions are separated from the dermis by an 800 Å thick basement membrane. Granule containing cells in the upper dermis send processes up to the cuticle where they are bound to the typical epidermal cells by septate desmosomes. The abundant membrane bound granules of the cells enter villous-like processes which pass through the cuticle. The function of these cells may be to produce an adhesive material on the podia or they may be pigment cells.The thick dermis consists of a superficial zone, containing largely ground substance; a middle or laminated zone containing laminae of collagen fibers arranged in an orthogonal fashion; and a hypodermis consisting largely of ground substance and reticular fibers. Fibroblasts are abundant in the superficial dermis and between the collagen laminae. Wandering coelomocytes, or morula cells, accumulate between the collagen laminae and in the hypodermis. They may also become an integral part of the epidermis by forming septate desmosomes with epidermal cells. Morula cells contain highly specialized spherules whose tinctorial properties and electron microscopic appearance suggest that they contain protein and mucopolysaccharide.

Notes: (1) The frontal wall of the encrusting cheilostome, Watersipora arcuata is a one-layered, evenly perforated calcareous shield which subdivides the metacoel into two compartments, the perigastric coelom and the hypostega. These compartments communicate through four and six “intrazoidal septulae” at the corners of the frontal wall. (2) The frontal wall develops by apposition independently of the ectocystal epitheca. The ascus develops as an invagination of the epitheca. These observations are consistent only with the view that the frontal wall of this species is a cryptocyst. (3) The terms “tremocyst,” “olocyst,” and “pleurocyst” are poorly understood and ambiguously defined; they should not be used until more information is available. (4) The taxa Anasca, Ascophora, Ascophora Imperfecta, and Ascophora Vera are polyphyletic and should ge dropped and replaced by Silén's (1942) more natural taxa. Silén's Cryptocystidea should be enlarged to include Watersipora and related ascusbearing cheilostomes.

Notes: Retrogressive analysis of the cn gene effect has been performed on crooked neck dwarf chick embryos between stages 28-38 (5-12 days). The phenocritical stage of mutant embryos studied is stage 29. Histolytic degeneration of neck tissues is first recognized by the appearance of localized degenerate nuclei in the tracheal mesenchyme. Pleiotropic autolysis of the embryonic thymus, loose mesenchyme and the ventral neck tissue is also observed. Histolysis occurs in a caudocephalic gradient in all cn-affected embryos. The degenerative effects in crooked neck dwarf embryos vary in their intensity, but the pattern of autolysis seems constant. Histological observations provide some explanation for “escapers,” homozygous lethal embryos known to survive until hatching. A mechanism for surviving developmental crises in cn embryos is proposed.

Notes: The placental memebranes and uterus of the garter snake, Thamnophis sirtalis, were studied using histological, histochemical, electron microscopic, dye transfer, and radioisotopic techniques. The conceptuses are completely enclosed throughout gestation by a transparent shell membrane which is produced by glandular epithelia in the uterine segment of the oviduct.Both chorio-allantoic and omphalo (yolk-sac) placentation are observed in this snake. The growth of the extra-embryonic mesoderm takes place in a manner peculiar to placental reptiles, and results in the isolation of the omphaloplacenta from the yolk-sac wall. On the basis of morphology, enzyme histochemistry, and phagocytosis of Trypan blue particles, this structure is interpreted as a site of histiotrophic absorption.The chorio-allantoic region of placentation is simple in structure. Fetal and maternal capillaries are closely apposed but always separated by layers of uterine and chorionic epithelium and the thin shell membrane. The placental membranes of the garter snake are similar in many respects to those of other live-bearing snakes, but less specialized than most lizard placentate.Isotopically labelled sodium and glycine are passed to the fetus following maternal injection, the latter at least apparently via the omphaloplacenta. The permeability to iron and phospate is extremely low. On the basis of these results and the selective transfer of certain dyestuffs, it appears that the shell membrane functions as a dialyzing membrane.

Notes: Light organs of larval photurid fireflies, which emit their light in a steady glow, differ from those of adults, which have a precisely controlled flash pattern, in having no specialized tracheal end organs and no morphologically distinct cortical region of the photocytes. However, like the adult organs, larval lanterns are abundantly supplied with both tracheoles and nerve fibers. Each of the two abdominal light organs of the larva consists of a dorsal (“reflector”) layer and a conical ventral photogenic layer. The dorsal layer is a single layer of columnar cells containing “urate” granules, mitochondria and a rich supply of glycogen. The photogenic layer is a compact mass of photocytes, containing photocyte granules similar to those of the adult organ, many elongated mitochondria, and a vesiculated reticulum. Numerous tracheoles run between the interlocking membranes of the photocytes. A large nerve traverses the dorsal layer and enters the photogenic layer, where its fibers diverge between the photocytes. Many structures having the appearance of neurosecretory nerve endings are found among the folds of the photocyte membranes. However, no tight junctions (synapses?) were found.

Notes: Spermatozoa of the hydroid Pennaria tiarella were examined with the electron microscope. The anterior region is characterized by the presence of 30-40 membrane-bounded vesicles which lie anterior to the nucleus. These vesicles are apparently derived from the Golgi apparatus.The nucleus is conical in shape with a protrusion at the anterior end. Posteriorly it is indented by four radially arranged mitochondria. Lying within the fossa formed by the mitochondria are proximal and distal (filament forming) centrioles. The distal centriole is characterized by nine centriole satellite projections which emanate from its matrix. The tubules of the distal centriole are continuous with the alpha filaments of the tail.The tails are typical 9 + 2 flagella with 9 peripheral doublet (or alpha) filaments surrounding two central (or beta) filaments.

Notes: The present work describes the ultrastructure of the spinal cord in the regenerating tail of the lizard, Anolis. The distal growing region of the tail contains the advancing ependymal tube which is relatively devoid of axons but already contains channels between ependymal cell processes which anticipate their ingrowth. More proximally, fascicles of naked axons having their origin in the stump are present in the ependymal channels. Therefore, the pattern of fiber regeneration in the spinal cord is prescribed by the ependyma and not by the growing axons. Details of the ultrastructure of proximal, intermediate, and distal regions of the regenerate are reported. Particular attention is paid to the structure and differentiation of the ependymal cells and the relation of the ependyma to other glial cells, to nerve fibers, and to meningeal tissues.

Notes: A mass of pineal tissue has been observed associated with the habenular commissure and the apex of the pineal recess in the golden hamster. Previously, it had been thought that all of the pineal system in the hamster was located at the confluence of sinuses just beneath the skull. To distinguish the two components of the pineal system, that in the dural position is called the superficial pineal and the mass associated with the habenular commissure is called the deep pineal.

Notes: The histology of the alimentary canal is described for the last instar larva, pupa, and adult Hyalophora cecropia (L.). Particular attention is given to the changes occurring in the midgut during the larval-pupal transformation and in the hindgut during the pupal-adult transformation. Descriptions are made as to the nature of the imaginal rings at each end of the midgut and a new structure is described in the larval ileum. The formation of adult rectal pads is followed in detail.

Notes: In Drosophila melanogaster embryos cuticle formation occurs between 12 and 16 hours of development at 25°C. The formation of the cuticulin and the protein epicuticular layers is simultaneous in the hypoderm, the tracheoblasts, and the fore- and hindgut cells. The cuticulin forms as a dual lamina, aggregating from granules secreted by the hypodermal cells. This is followed by the formation of a granular protein epicuticle and finally by the secretion of a mixed fibrous and granular endocuticle.All secretory cells are relatively simple in their ultrastructure. The secretory process is a membrane phenomenon, occurring at the tips of hypodermal microvillae on cells at the surface of the embryo and on those hypodermal cells lining the lumen of the fore- and hindgut. It also occurs along the entire surface of the tracheoblast lumen as well as on the outer surface of those cells which form exoskeletal chitinous setae. The process involves a specialization of the plasma membrane with the formation of secretory granules intracellularly beneath the membrane and the extrusion of these granules through the membrane to the outside where final cuticle formation occurs.

Notes: Pygidial defence glands, which are universal in Caraboidea, are paired, cuticular invaginations of the body wall.In Pterostichus madidus F. the glands contain a nauseous, corrosive secretion that can be discharged forcibly to deter attack by predators. The cells producing the secretion are of one type only. Electronmicroscopy shows that the ducts which drain these cells are not intracellular but are separated from the cell contents by a plasma membrane. The cuticular walls of the duct appear to effectively screen the cell from the disruptive effect of its final products of secretion. The duct-carrying epidermal cells which are modifications of the epidermis covering the rest of the gland support the ducts from the secretory vesicles to their entry into the central lumen of each secretory lobe. There is a single duct-carrying cell around each duct.

Notes: The oöcyte of H. grisea is surrounded early in its growth by the accessory cell. A yolk halo, secreted by accessory parenchymal cells, subsequently envelops the oöcyte and its accessory cell. Of particular interest are the supernumerary asters, and their central bodies, which surround the oöcyte nucleus. The asters are exceptional because they appear in unfertilized oöcytes with (apparently) intact germinal vesicle membranes. Coincident with sperm penetration the supernumerary asters grow. Their rays elongate and thicken. The nuclear membrane disappears. The supernumerary asters aggregate and disappear prior to the maturation (meiotic) divisions. The maturation asters from with distinct centrioles and centropheres while the egg is still within the parenchyma of the worm. Their formation is independent of sperm penetration. The polar bodies are given off within the cocoon.

Notes: Study of a series of embryos showed that the spiroboloid leg arrangement (1 pair of legs on each of the first 5 segments) is derived from the typical leg arrangement (no legs on segment 1, 1 pair on segments 2 through 4, and 2 pairs on segment 5) by a shifting forward one segment of the first four pairs of legs.A careful re-examination of the literature, especially papers by Robinson ('07), Silvestri ('03, '49), Pflugfelder ('32), and Manton ('61), combined with observations of Narceus embryos led to the conclusion that (1) the anterior body segments are primatively single (2) the gnathochilarium is composed of only one pair of mouthparts, the diplopod head having but two gnathal segments, and (3) the intercalary segment is present in the Diplopoda.

Notes: Several oxidative enzymes in the testis of the teiid lizard Cnemidophorus tigris were studied histochemically. The cells of the circumtesticular sheath (Leydig cell tunic) are functionally equivalent to Leydig cells of the interstitium on the basis of similar histochemical reactions for the five enzyme systems studied. Both groups of cells were positive for 3β-hydroxysteroid dehydrogenase, 17β-hydroxysteroid dehydrogenase, NADH diaphorase, NADPH diaphorase, and glucose-6-phosphate dehydrogenase. These results support the hypothesis that the circumtesticular sheath has endocrine function as indicated by its vascularity and its ability to catalyze histochemical reactions involving steroid biosynthesis.

Notes: If that portion of a chick embryo destined to form the eye, the lens, part of the brain and the surrounding head region be removed from the chick before the lens has begun to develop, and placed in a liquid culture medium for four days, a structure resembling the lens will form in appropriate proximity to the presumptive retina, and the cells of the lens will synthesize proteins unique to and characteristic of the lens. The time course of morphological development of such explants is here described.In vitro the lens placode dose not invaginate to form a lens vesicle, as it does in ovo. Instead placode cells elongate directly to form fibre cells. The shape of the lens formed in this aberrant manner is remarkably similar to that of normal lens.At least one, and probably all three, of the characteristic crystallins of the lens form in these aberrant lenses, the cytological and biochemical differentiation of which proceeds normally, despite failure of the normal morphogenetic activities of the organ.

Notes: The external prostate of male hedgehogs (Erinaceus europeus, Hemiechinus sp.) was studied at the beginning and at the end of the breeding seasons. Its tubular secretory units contain two types of epithelia, columnar and stratified. The columnar epithelium has abundant rough endoplasmic reticulum and forms secretory granules. The stratified epithelium undergoes cellular changes culminating in appearance of nuclear and cytoplasmic inclusions, nuclear pyknosis and desquamation of cells and nuclei into lumen. The nuclear inclusions contain protein and abundant silver-reducing substances. These inclusions may be derived from the residual protein of the nucleus.

Notes: In squirrel monkey (Saimiri sciureus) the position of submandibular glands in the neck, on either side of the trachea, more closely resembles that of rodents than that of other primates. The glands exhibit seromucous acini and mucous tubules with seromucous demilunes. Electron microscopy shows basal cytoplasmic folds and well-developed intercellular tissue spaces and canaliculi only in relation to seromucous cells. Greatly dilated cisternae of the granular endoplasmic reticulum and prominent Golgi membranes are characteristic of the mucous cells. The secretory granules of seromucous and mucous cells are morphologically distinct and indicate chemically different products for the two cell types. Histochemically, the seromucous cell shows the presence of acid mucosubstance as indicated by the PAS and Alcian blue techniques. Preliminary studies showed no appreciable quantity of amylase in submandibular glands. The intercalated duct cell is juxtaposed with the acinar cell or mucous tubule cell. Short luminal microvilli, prominent Golgi complexes and scant apical granules are notable features of intercalated duct cells. Four cell types compose the striated ducts, viz., granular light cells, agranular dark cells, vesiculated dark cells, and basal cells. Peripheral nerves are found in five different locations: in the connective tissue (interstitial), between adjacent myoepithelial and mucous-secreting cells, in the intercellular space between adjacent secretory cells, and between basal plications of striated ducts and between adjacent myoepithelial and intercalated duct cells.

Notes: The organization of the corpora cardiaca and corpora allata of the female alfalfa weevil, Hypera postica, generally parallels that reported for other insects with extrinsic neurosecretory axons, intrinsic neurosecretory cells, and interstitial or glial cells appearing in both glands.Connecting the brain with the cardiacum are the extrinsic neurosecretory axons containing granules between 600 and 2200 Å. Granules with a diameter of up to 4000 Å are found in the intrinsic secretory cells of the corpus cardiacum.From the lobed corpus cardiacum, axons extend along a short nerve trunk into the ovoid corpus allatum. A characteristic of this gland is the presence of a layer of axons, ensheathing most of the corpus allatum and situated beneath an external basement membrane. These axons are believed to have their origin in the protocerebral neurosecretory cells. Although the c. allatum is known to be engaged in the release of hormonally active material, the cytoplasmic organization does not strongly reflect such activity.The glands of the diapausing weevil appear similar to those of the active weevil with a reduction in cytoplasm and a consequent folding of the plasma membrane.

Notes: The mitotic and labelling incidence of intestine, liver, spleen and pancreas cells of Triturus cristatus carnifex adults kept at 15°C, 20°C, 25°C and 30°C were examined. Intestine mitotic and labelling incidences were highest at 25°C and lowest at 30°C. There was no significant difference between 15°C and 20°C. No such relationship could be shown for liver, spleen or pancreas, which had very much lower mitotic and labelling incidences. In culture, intestine mitotic and labelling incidences fell significantly within the first four hours, and maintained these low levels for the next five days. In contrast, liver mitotic and labelling incidences rose for 9-11 days, and then began to fall, while pancreas mitotic and labelling incidences reached peak values at day 5, and were kept in good condition for up to 14 days.

Notes: The venous system of the head and neck of the opossum, Didelphis virginiana, was studied by injecting the veins with a tinctorial mass. Gross dissection spechmens injected with a colored gelatin solution and corrosion specimens prepared by Batson's technique (Batson, '55) were utilized to describe the venous pattern in greater detail than is presently available in the literature. The venous drainage of the superficial structures of the head is principally by way of the V. jugularis externa and its tributaries. Although small emissary veins connect the Sinus cavernosus with the Plexus pterygoideus and the V. maxillaris, the dural venous sinuses drain primarily into the Plexus vertebralis internus and into the V. maxillaris by way of the V. emissaria foraminis retroarticularis. The small V. jugularis interna receives minor connections from the Plexus pterygoideus, the Sinus cavernosus and the Sinus petrosus ventralis as well as anastomotic tributaries from the Plexus vertebralis and the plexus of veins around the hyoid bone. However, the V. jugularis interna serves mainly as a pathway for venous drainage from the deeper structures of the neck and only minimally for draining the brain.

Notes: The ontogeny of amphicoelous vertebrae was studied in Ptyodactylus hasselquistii and Hemidactylus turcicus, and that of procoelous vertebrae, in Sphaerodactylus argus. The embryos were assigned arbitrary stages, drawn to scale, and mostly studied in serial sections.Resegmentation occurs as in all amniotes. A sclerocoel divides each sclerotome into an anterior “presclerotomite” and a denser posterior “postsclerotomite.” Tissue surrounding the intersegmental boundary forms the centrum, which is intersegmental. Tissue around the sclerocoel builds the intervertebral structures, which are midsegmental. In the trunk and neck, postsclerotomites form neural arches, and presclerotomites build zygapophyses.The adult centrum consists of the perichordal primary centrum, plus neural arch bases (= secondary centrum). Between the latter and the arch proper, a neurocentral suture persists until obliterated in maturity. A dorso-ventral central canal persists on either side of the primary centrum, between the latter and the secondary centrum.The notochord becomes true cartilage midvertebrally in all vertebrae, and elastic cartilage intervertebrally in the posterior caudal region. Elsewhere its characteristic tissue persists.Intervertebrally, cervical hypapophyses, caudal chevrons and chevron-bases in the trunk are preformed early in cartilage. Directly ossifying median intercentra are added later in all regions.The first cervical presclerotomite is absent: the hypapophysis (= corpus) of the atlas consists exclusively of postsclerotomitic tissue, there is no proatlas, and the odontoid lacks the apical half-centrum present in other lepidosaurians.In the autotomous caudal region presclerotomites are as prominent as postsclerotomites. Both build neural arches, the two arches of each vertebra remaining distinct and ossifying separately, so that the intersegmental autotomy split persists between them.The last sclerotome is complete, its postsclerotomite forming a half centrum which ossifies.In Sphaerodactylus, while the vertebrae ossify, each intervertebral ring becomes concave anteriorly, convex posteriorly; it remains as a cushion between the condyle and a facet formed by differential growth of the centra. Thus these procoelous centra resemble the amphicoelous centra of Ptyodactylus and Hemidactylus, rather than the procoelus centra of other squamates.The vertebral column of Gekkonoidea closely resembles in its development and microscopical structure that of Sphenodon.

Notes: Within the supraesophageal ganglion of polynoids is a vertical fiber tract which has the appearance of a “Y” in transverse sections of the brain, and contains the axons of many neurosecretory cells. The granule-filled terminals of these neurosecretory fibers are found at the base of the tract where they are in contact with the inner surface of the sheath covering the ventral surface of the brain. This sheath separates these neurosecretory endings from an underlying pericapsular epithelium which is thicker in this region. Beneath this pericapsular epithelium is a coelomic sinus. The dorsal blood vessel is located within this sinus and is “innervated” by a pair of fiber bundles that pass out of the brain at the base of the vertical fiber tract. The outer surface of the vessel is covered by epithelioid cells which contact these fiber bundles and the thickened pericapsular epithelium, and sometimes contain granular cytoplasmic inclusions. The lumen of the vessel is continuous with the lumina of a pair of cellular, thickwalled structures of unknown function which are attached to the ventro-lateral margins of the brain. The relationship between neurosecretory endings, enlarged pericapsular cells, coelomic sinus and blood vessel provides morphological evidence for the hypothesis that these structures are elements of a neuroendocrine system, similar in some respects to the brain-infracerebral gland complex of nereid and nephtyid polychaetes.

Notes: The endodermal nerve nets of the scyphozoan jellyfish Phacellophora camtschatica and Cyanea capillata were stained with methylene blue. Small animals (3-7.5 cm in diameter) stained easily. The endodermal nerve net of both species is a synaptic net consisting of bipolar and some few tripolar nerve cells with unbranched neurites. The neurites terminate on other neurites. Very few free nerve endings were observed. The neurites have a diameter of 1/4-1/2 μ and there is no indication of the presence of neurites too fine to be followed in the light microscope.The gross appearance of the net changes with the size of the medusa. Staining 15-53 cm diameter animals showed that the nerve cells increase in size with the size of the animals, that the density of the nerve net decreases.The endodermal nerve net is very similar to our interpretation of the Diffuse Nerve Net of the ectoderm but without the typical primary sense cells. In both cases the appearance of branching neurites is interpreted as an artifact caused by neurites terminating on other neurites.

Notes: The bodies of adult and fifth instar Notonecta possess external air stores which are periodically renewed at the surface of the water. Both nymphs and adults have large ventral air stores on the thorax and abdomen and obtain atmospheric air at the posterior end of the latter; the adult also has dorsal subalar and supra-alar air stores on both these regions. Ten pairs of spiracles open onto the air stores. Although the seven small, ventrally placed abdominal spiracles are probably both exhalant and inhalant in nymphs and adults, the three large anterior spiracles (mesothoracic, metathoracic, and first abdominal), which play a more important respiratory role, appear to function differently in mature and immature Notonecta. In the nymph they are probably both inhalant and exhalant, and communicate broadly with each other and with the ventral air stores. In the adult, however, they open onto separate, air-filled chambers, each of which communicates differently with various parts of the air stores. Although all three probably function in exhalation, only the first abdominal spiracle, whose spiracular chamber is widely continuous with the dorsal and ventral air stores, appears to be well suited for inhalation.Several morphological features, most notably the development of long prothoracic lobes, separate spiracular chambers, and long, movable forewings, allow the adult a greater variety of respiratory modes than are available to the nymph. Some of the respiratory advantages of the adult are: (1) a larger amount of stored air; (2) a longer subalar air store, which can serve as an alternate pathway between the air stores and the atmosphere; (3) a greater capacity to utilize dissolved as well as atmospheric oxygen; (4) greater separation and functional specialization of the three anterior spiracles, thus allowing more separation of exhaled air from oxygen-rich air on the external surface of the thorax; (5) the probable ability to regulate the continuity between various parts of the air stores, thus utilizing alternate pathways of air circulation and/or changing the functions of the three anterior spiracles; and (6) better protection of the latter against the entry of water during prolonged submergence.

Notes: The antennal flagellum of the male sorghum midge is about a millimeter long and may bear over 500 sense organs. These consist of (1) tactile hairs, (2) thin-walled pegs, (3) circumfila and (4) very small pegs of unknown function. Each of the 12 subsegments of the flagellum is divided into two globular nodes and each of these is encircled by a circumfilum of from 6 to 14 loops. The circumfila are attached to the antennal surface by short stalks. The loops of the circumfila have the basic structure of thin-walled chemoreceptors: (1) very small pores in their delicate wall and (2) a lumen filled with branches of dendrites from sensory neurons. The outer surface of the circumfilum is covered with a labyrinth of fine ridges between which the pores are located. Some evidence was obtained that the circumfila are produced in the pupa by bifurcate trichogen cells.The flagellum of the female is shorter than that of the male and composed of 12 cylindrical subsegments. The circumfila of the female lie close to the surface to which they are attached by short stalks. Each is composed of two parts that encircle the subsegment and of two others that run lengthwise between the circles. The surface is nearly smooth, perforated by fine openings and lacks the complex pattern of ridges seen in the male. It also has more dendrite branches but, otherwise, has the same basic structure.

Notes: The fine structure of the excretory tubes of the mesostigmatid mite Macrocheles muscaedomesticae were investigated. These paired tubes are partially ensheathed by fat body and invested throughout by a branching system of visceral muscles. The fine structure of the cells of the excretory tube is in general similar with only minor differences found throughout its length. The basal region of each epithelial cell of the excretory tube borders the hemocoel and is divided into many compartments by the extensive infolding of the plasma membrane. Mitochondria and vacuolar inclusions are often closely associated with these compartments. More than one morphological type of mitochondria was found distributed throughout the cells of the excretory tubes. The most commonly encountered type had well developed cristae and an electron dense matrix. Less commonly, mitochondria with somewhat poorly developed cristae and a translucent matrix often containing myelin-like figures of varying complexity were observed. It is suggested that they represent part of a normal process of mitochondrial degeneration. The apical region of the cell has a border composed of plate-like folds of the plasma membrane termed microlamellae. The lumen contains abundant granules of the excretory product.

Notes: In the course of this investigation 24 fetuses of the Sprague-Dawley rats were used. Pregnant animals were sacrificed at 12, 14, 16, 18, and 20 days of gestation. The fetuses were removed and fixed in buffered formalin solution. The heads were dehydrated, embedded in paraffin, and the nasal cavities were sectioned serially. Light microscope observations were made on 10 to 15 μ thick sections stained with H and E, Mallory's trichrome stain, and Gomori's alkaline phosphatase stain. The 12 day old fetus possessed well developed olfactory depression with a thick epithelial covering. The olfactory fossa was still separated from the buccal cavity by a solid layer of young mesenchyme. In the 14 day old fetus the communication between the nasal and buccal cavities was established. The palatal shelves developed still vertically. All the turbinates and the nasal capsule were already differentiated. The glandular system was represented with the main and two to three accessory excretory ducts. During the sixteenth day of prenatal development, the sinus and the sinus related glands became for the first time evident. The ossification of the membranous parts of the lateral nasal wall was initiated. In the next two developing stages the maturation of the cartilage, the increasing ossification in the membrane, and the further differentiation of the glands were the major morphological changes in the formation of the lateral nasal wall.

Notes: The histogenetic and organogenetic capabilities of normal and lobeless embryos of Ilyanassa obsoleta are analyzed. Larvae developed from eggs in which the polar lobe was removed at the trefoil stage of first cleavage were studied in wholemount and section. None showed any evidence of eyes, statocysts, operculum, external shell, heart, or intestine. Sixty per cent of the wholemount larvae observed under polarized light exhibited internal masses of birefringent material resembling shell material. Of eight- to nine-day lobeless larvae studied as stained, sectioned material 100% possessed muscle tissue; 97.5% possessed velar tissue, digestive gland tissue, and style sac tissue; 52.5% possessed two or more style sac areas; 71% exhibited esophagus; 63% possessed stomach tissue; 37% exhibited stomodeal-like invaginations of the ectoderm; 31% exhibited a lightly staining ciliated area at the tip of the prevelar ectoderm; and 21% possessed glandular ectoderm resembling pedal or mantle gland tissue.The evidence presented suggests that the material of the polar lobe has an important role not only in cellular differentiation but also in the organization of tissue types into organs or organ primordia.

Notes: The adventitia of the crayfish heart is composed of cells that are separated from each other by an intercellular space about 280 Å wide. Desmosomes are present on apposing surfaces of adjacent cells. A basal lamina underlies the adventitia and consists of a dense, amorphous substance that contains numerous fine filaments.The myocardial cells are striated and an external lamina 0.1 μ thick is present on the surface of the plasma membrane. The nuclei and most of the cytoplasm, glycogen and mitochondria are located at the cell periphery. The myofibrils are composed of thick and thin filaments and confined to the core of the cell. A T system and a well-developed SR are present. Elements of these organelles form dyads at levels that correspond to the H bands, and triads at levels that correspond to the Z bands of the peripheral myofibrils. The relationship of the T tubules to the myofibrils is discussed.Locus cells exhibit a unique pattern of intracellular myofibrillar branching. They branch from a region which has a structure similar to the Z band material. The myofibrils radiate outwardly in various directions and form numerous cellular branches which form intercalated discs with adjacent myocardial cells. These discs are more complex than those observed in poikilothermic vertebrates but are simpler than those in mammals.An endocardium is lacking in the crayfish heart but interstitial cells are present in close association with the myocardial cells and neural elements. Terminal nerve processes deeply embedded in the myocardial cells are described.

Notes: Walking of Chrysemys has been studied by cinephotography and x-rays. The lateral sequence, diagonal couplet gait, limb support sequence, and wide track provide great stability, yet a slight pitch and roll cause some plastral drag. Velocity ranges from 28 mm to 51 mm/second, and fluctuates within a stride. Limb movements and structure resemble those of other ectotherms, but incorporate modifications reflecting the animal's short, broad trunk encased in a shell and carried close to the ground. The triradiate pectoral girdle so articulates with the shell as to act as a truss for weight transfer to the ground. Girdle rotation increases the efficiency of the girdle as a truss, and contributes to locomotor efficiency. The glenoid cavities are more than twice as far apart as the acetabula, so a thrust from the pectoral girdle has less propulsive efficiency on the center of gravity than one from the acetabulum. The humerus and femur are protracted to a greater extent than in other ectotherms and their horizontal arcs of retraction are less. Rotation of these elements about their longitudinal axes contributes to the length of a stride and to foot placement and withdrawal. Differences in the movements of comparable segments of front and hind limbs correlate with differences in the width of the girdles, a crus longer than the antebrachium, and different capacities for joint rotation.

Notes: Queen butterflies do not mate until the male has brushed the tufts of his scented, abdominal “hairpencils„ over the female's head and antennae. The trichogen cells located at the base of each hairpencil are secretory. Presumably, these cells produce the sex pheromone necessary for mating. The liquid secretion must move from a central, microvillus-lined vesicle through the cuticle of the hairs to coat numerous, free, cuticular „dust“ particles which adhere to the hairs' surface. The dust carries the secretion to or near the female's antennae. In the pupal stage the dust particles develop as outpocketings of the hair epicuticle. An amorphous matrix, probably protein epicuticle, is deposited in the outpocketings between the cuticulin layer and plasma membrane of the hair. Before the butterfly emerges from the pupa the matrix becomes enclosed by cuticulin, and the particles pinch off from the hair.

Notes: Light microscopy of serially sectioned nasopalatine duct remnants in ventral rostral integument of four adult (2 ♂, 2 ♀) fin whales reveals: (1) a common structure in all, (2) blindly ending nasopalatine pits 4 to 9 mm deep, (3) solid epithelial duct remnants 12 to 15 mm long, (4) lack of chemoreceptor endings, and (5) an abundance of presumed mechanoreceptors, mostly of the Pacinian category on the adoral sides, but also including some thinly encapsulated and perivascular ones that extend into the abundant connective tissue papillae of the duct remnants. Comparative and evolutionary relations of these structures are discussed.

Notes: A morphohistological study was carried out on the pineal organ in 15 species of teleosts belonging to 12 different families. In spite of a general similarity in pineal structure in different species, there is evident a systematic diversity. The majority of species possess saccular pineal organs containing photoreceptors as prominent parenchymal components. The close anatomical relationship of the pineal organs with the relatively thin cranial roof further supports the photosensory nature of this organ in most species. However, in certain species, particularly Corydoras aneus, apparent paucity of sensory cell outer segments, parenchymal proliferation, epithelial compactness and rich vascularization suggest specializations for a predominantly nonsensory and possibly secretory function. On the other hand, the preponderance of sensory cells in the pineal organ of Symphysodon aequifasciatus and Gyrinocheilus aymoneri indicates exceptional adaptitions for a predominantly photosensory role. The results are discussed in the light of existing electron microscopic and biochemical investigations which support a secretory function of fish pineal. The need for proper selection of species for future research on pineal function is emphasized.There is also evident a close anatomical relationship between the pineal organ, the dorsal sac and the third ventricle in various species. The possibility of intramural functional relationship of the pineal with these structures and the brain is suggested.The presence of intrapineal neurones and an afferent (pinealofugal) innervation in majority of species is described. The tractus pinealis enters the posterior commissure area. In rainbow trout, Salmo gairdneri, some branches, right and left, leave the posterior commissure and could be seen to move toward the habenular ganglia. Their destination remains unclear. In jack smelt, Atherinopsis californiensis, a major bundle of tract fibres follows the ventral aspect of the posterior commissure reaching what may be nuclei dorsomedialis-dorsolateralis. The possibility of direct connections with the fasciculus retroflexus is suggested. No evidence could be provided supporting existence of an efferent (pinealopetal) innervation of parenchymal cells in the pineal of species studied. It is pointed out that clarification of this aspect in future is important for a proper understanding of metabolic aspects of pineal organs in fishes.

Notes: Examination of the cardiac anatomy of lizards of the family Varanidae revealed that much of the previous literature contained basic errors both in description and interpretation. These are corrected and terminology of various authors is standardized.The varanid ventricle is similar to that of most other lizards in not being elongated, in having the base at right angles to the longitudinal axis, and in having the vertical septum weakly developed. However, it is not a typical lacertilian heart in that it has a number of characteristic ophidian features such as a muscular cone surrounding the cavum latero-dorsale and a prominent twisting of the cava. It lacks a gubernaculum cordis and a cartilaginous rod in the septum aortico-pulmonale, both of which are present in many non-varanid lizards, but seldom occur in snakes. The location of the heart is more posterior in the body than is true of other lizards.

Notes: Light microscope studies were made on nucleoli of jejunal epithelial cells of normal rats fixed in OsO4, glutaraldehyde, F.A.A. and HgCl2 and stained with basic fuchsin-alkaline methylene blue. Nucleolar reorganization is extensive and clearly resembles the phenomenon of nucleolar segregation. Polymorphous nucleoli of undifferentiated crypt cells show intermingled constituents and stain purple whereas similar nucleoli of definitive absorptive cells show two homogeneous components-A, stained red and B, stained blue. Cytochemical studies indicate that component A is largely protein and acidophilic and component B is largely nucleic acids and basophilic. These nucleoli become compacted, each forming an amphinucleolus with the two components at opposite poles. Further changes occur along the villi and the components generally separate to form a condensed plasmosome and a diffuse karysome. Extruded cells show nucleolar fragmentation.Electron micrographs of OsO4 material were used in preparation of wax models. These, along with electron micrographs of glutaraldehyde material stained with uranyl acetate and lead citrate, clearly illustrate and duplicate light microscope findings and strongly resemble nucleolar segregation produced by antimetabolites.Cells of the villi with reorganized nucleoli do not undergo mitosis whereas undifferentiated crypt cells do so. Furthermore, nucleolar reorganization is correlated with aging since it begins in crypt cells and culminates in senescent cells at the tips of the villi.A review is given of the extensive evidence showing that, in the intestine certain functional changes occur similar to those demonstrated in experimental nucleolar segregation. These include gradually changing patterns of DNA, RNA and protein synthesis as well as enzyme activity. The accompany and probably result from nucleolar reorganization.

Notes: The stellate cell in the pars distalis of Anolis carolinensis has been studied with the electron microscope. This cell type is characterized by the lack of secretory granules, and it possesses elongate processes that insert between secretory cells. Few cytoplasmic filaments are present in these processes, and desmosomes linking them to adjacent stellate cells or to secretory cells are seen infrequently in control animals. Stellate cells are often encountered in the caudal half of the pars distalis, but they are less commonly found in the rostral half. In animals undergoing thyroidal depression, thyroidectomy cells arise in the caudal pars distalis. Concurrently, stellate cells of that region hypertrophy and exhibit increased numbers of desmosomes, complex intercellular junctions, and micropinocytotic vesicles. Injected horseradish peroxidase penetrates the intercellular spaces, enters the micropinocytotic vesicles, and is transported to the interior of the stellate cell. It is suggested that stellate cells in Anolis under certain conditions may transport materials between the bloodstream and secretory cells.

Notes: The early development of five species of substrate-brooding cichlid (Aequidens pulcher; Cichlasoma bimaculatum; C. biocellatum; C. nigrofasciatum and Hemichromis bimaculatus) is described. Heterochrony in these species renders the standard system of staging inadequate for comparative study. A new system is proposed in which the period of development is resolved into five overlapping phases, each phase corresponding to a dissociable ontogenetic process. This form of staging permits comparison in a way which neither obscures the basic uniformity of cichlid development nor masks the differences between the species.Two special features are discussed: the universal presence in substrate-brooding cichlids of three pairs of embryonic adhesive organs; and the apparent presence of non-neural crest pigment on the embryos and alevins.

Notes: Development of villi in the duodenum of the chick was studied in stages ranging from 11 days of incubation to one week after hatching. Formation of definitive villi is preceded by development of a set of previllous ridges that run lengthwise along the duodenum. The first set of 16 previllous ridges (Set I) is complete by about 13 days of incubation; all ridges in the set are fairly uniform and proceed through their subsequent development in synchrony. Previllous ridges in Set I fold into a highly regular zigzag pattern between 14 and 16 days of incubation. Definitive villi develop from Set I ridges beginning at about 17 days when populations of distinct cells appear on the crests of the ridges between angles in the zigzag folds. Cells in these populations lack the rounded appearance of cells seen in earlier stages; their apical surfaces are densely covered with microvilli. A second set of villi (Set II) develops at about 16 days of incubation when about 16 rows of tongue-like flaps erupt between the previllous ridges of Set I. At hatching, Set II villi are still smaller than villi of Set I; this distinction disappears by about the fourth day after hatching. The significance of the morphological changes in epithelial cells is discussed in terms of several hypotheses bearing on the mechanisms of villus formation.

Notes: Early descriptions of insect sensory organs included three presumed mechanotransducers in the tibia of Orthoptera, namely the subgenual organ, the intermediate organ, and the tympanal organ. This investigation re-evaluates the light microscopic appearances of these organs in the foreleg tibia of the cricket, Gryllus assimilis, initially described by Herbig in 1902.The study also examines the fine structure of the subgenual and intermediate organs and provides the first fine structure analysis of these structures.The subgenual and intermediate organs are typical scolopophorus organs suspended perpendicular to each other within the dorsal hemolymph canal. Each is innervated by dendrites from the anterior ganglion. Neither the subgenual, intermediate, nor tympanal organ is structurally related to the larger posterior tympanic membrane.The study shows that the tibial tympanal organ in the cricket is not a scolopophorus organ, but consists of highly modified epithelium, associated with the anterior tympanic membrane, and receiving innervation from the anterior ganglion.

Notes: The structure of the caudal muscle in the tadpole larva of the compound ascidian Distaplia occidentalis has been investigated with light and electron microscopy. The two muscle bands are composed of about 1500 flattened cells arranged in longitudinal rows between the epidermis and the notochord. The muscle cells are mononucleate and contain numerous mitochondria, a small Golgi apparatus, lysosomes, proteid-yolk inclusions, and large amounts of glycogen. The myofibrils and sarcoplasmic reticulum are confined to the peripheral sarcoplasm.Myofibrils are discrete along most of their length but branch near the tapered ends of the muscle cell, producing a Felderstruktur. The myofibrils originate and terminate at specialized intercellular junctional complexes. These myomuscular junctions are normal to the primary axes of the myofibrils and resemble the intercalated disks of vertebrate cardiac muscle. The myofibrils insert at the myomuscular junction near the level of a Z-line. Thin filaments (presumably actin) extend from the terminal Z-line and make contact with the sarcolemma. These thin filaments frequently appear to be continuous with filaments in the extracellular junctional space, but other evidence suggests that the extracellular filaments are not myofilaments.A T-system is absent, but numerous peripheral couplings between the sarcolemma and cisternae of the sarcoplasmic reticulum (SR) are present on all cell surfaces. Cisternae coupled to the sarcolemma are continuous with transverse components of SR which encircle the myofibrils at each I-band and H-band. The transverse component over the I-band consists of anastomosing tubules applied as a single layer to the surface of the myofibril. The transverse component over the H-band is also composed of anastomosing tubules, but the myofibrils are invested by a double or triple layer. Two or three tubules of sarcoplasmic reticulum interconnect consecutive transverse components.Each muscle band is surrounded by a thin external lamina. The external lamina does not parallel the irregular cell contours nor does it penetrate the extracellular space between cells. In contracted muscle, the sarcolemmata at the epidermal and notochordal boundaries indent to the level of each Z-line, and peripheral couplings are located at the base of the indentations. The external lamina and basal lamina of the epidermis are displaced toward the indentations.The location, function, and neuromuscular junctions of larval ascidian caudal muscle are similar to vertebrate somatic striated muscle. Other attributes, including the mononucleate condition, transverse myomuscular junctions, prolific gap junctions, active Golgi apparatus, and incomplete nervous innervation are characteristic of vertebrate cardiac muscle cells.

Notes: The scanning electron micrographs show the external morphology of the maxillae of Drosophila melanogaster. Specifically, they illustrate the patterning of the different types of chemo-receptive sensilla on the maxillary palpi making possible a clearer understanding of the structure of the tiny maxillary lobes. It appears that the maxillary lobes act as “cleaning brushes” during the feeding process.

Notes: This report presents light microscopic descriptions of lymphoid organs and aggregates in the snapping turtle Chelydra serpentina. The thymus and spleen were found to be similar to those of other ectothermic vertebrates. Certain gut associated lymphoid aggregates suggest the presence of reptilian equivalents of tonsils, Peyer's patches and the avian bursa of Fabricius. Lymphoid aggregates located in the axillary and inguinal regions were apparent for the first time in an ectothermic vertebrate. These are of particular interest since they may represent ancestors of true lymph nodes in analogous locations in mammals. It is concluded that the snapping turtle is not deficient in lymphoid tissue, although there is a conspicuous absence of typical germinal centers, characteristic of mammalian organs.

Notes: The guinea pig soleus muscle is a convenient model for the study of slow-twitch intermediate (STI) fiber ultrastructure because it is composed entirely of fibers of this class. Such fibers were compared with fast-twitch red (FTR) and fast-twitch white (FTW) fibers from the vastus lateralis muscle.FTW fibers are characterized by small, sparse mitochondria, a narrow Z line and, an extensive sarcoplasmic reticulum arranged primarily in longitudinal profiles at the A band and with numerous expansions at the I band. Abundant mitochondria with a dense matrix and subsarcolemmal and perinuclear aggregations are typical of FTR fibers. These fibers contain a plexus of sarcoplasmic reticulum at the A band and a less extensive network at the I band. The Z lines are wider (890 ± 74 Å) than those of FTW fibers (582 ± 62 Å). STI intermediate fibers are distinguished from other types by wide Z lines (1205 ± 58 Å), a faint M band, and a less extensive sarcoplasmic reticulum. Compared to FTR fibers, STI fiber mitochondria are usually smaller with less notable subsarcolemmal accumulations.FTW fibers have a more limited capillary supply, rarely contain lipid inclusions, and thus may be restricted to phasic activity. Extensive capillarity, mitochondrial and lipid context, and fast contraction times indicate possible phasic and tonic roles for FTR fibers. STI fibers, characterized by numerous lipid inclusions, extensive capillarity, relatively numerous mitochondria, but slow contraction-relaxation cycles, are morphologically suited for tonic muscle activity.

Notes: Four hemocyte types have been identified in the late last larval instar of Galleria mellonella. Plasmatocytoids are round to spindle shaped cells, 10-20 μ long and 5-10 μ wide. The cytoplasm contains no distinguishing inclusions. Golgi complexes, rough endoplasmic reticulum and free ribosomes are abundant. Granular hemocytes are oval shaped cells, 10-20 μ long and 5-10 μ wide. The granules, their most characteristic feature, have a diameter of 0.2 μ, a microtubular sub-structure, and are made up of acidic mucosubstances. Lipid droplets may be present in these cells at some stage of development. These cells appear to be phagocytic. Spherule cells are oval shaped, 15-20 μ long and 5-10 μ wide. The spherules, approximately 2 μ in diameter, have a highly ordered substructure and are made up of acidic mucosubstances. Oenocytoids are the largest cells, 20 by 40 μ. The cytoplasm contains mostly free ribosomes and microtubules.

Notes: The muscles of the head, neck and thorax of the adult cabbage looper Trichoplusia ni are described for the first time. They are compared to those of Choristoneura fumiferana, Manduca sexta, Smerinthus geminatus, Antheraea polyphemus, Sphinx convolvuli, Crymodes devastator, and Danaus plexippus.

Notes: Meiosis is described in virgin females, inseminated females and males of the acarid mite Caloglyphus mycophagus (Megnin). The observed sex determining mechanism is an XO-type with the male having a diploid chromosome number of 15. Oogenesis in mated females is regular. Pachytene is the earliest meiotic stage which is readily identifiable. At metaphase I eight bivalents are observed. Both products of the first maturation division divide at the second maturation division. After the fusion of the pronuclei either 15 or 16 chromosomes are observed in cleaving eggs.Nurse cells are not observed during the growth period of the oocyte. Such oocytes are attached to a central structure of the ovary by a cone-shaped organelle. At this stage the nucleus appears as a germinal vesicle; a nucleolus is present and the diffuse chromatin appears to extend from the nucleolus to the nuclear membrane. Nuclear extrusion bodies can be seen adjacent to the nuclear membrane both within and outside of the nucleus.Virgin females do not oviposit. The aberrant morphology and behavior of bivalents in post diakinetic oocytes which have not been penetrated by a sperm are described. Neither chromatin nor a chorion could be demonstrated in aberrant oocytes situated in the oviduct. It is suggested that oocyte degeneration in virgins is an adaptive feature in an animal order in which parthenogenesis is the more common mode of reproduction.

Notes: Observations on fine structure at the basal end of the intestinal epithelium in the midgut region of Balanus balanoides and Balanus improvisus reveal complex interrelationships among several tissues. Numerous elongate cell processes extend towards the intestinal epithelium penetrating between layers of intestinal muscle through blood spaces and into the basal lamina underlying the epithelium.Two types of morphological relationships occur between cell processes and the basal end of the intestinal epithelial cell: 1. The cell process may penetrate the basal lamina and lie closely apposed to the epithelium. 2. The cell process may give rise to narrow, medially-directed, finger-like extensions (projections). The narrow projections penetrate the basal lamina and, in addition, terminate as dilated bulbs within inpocketings of the epithelium. In some respects the cell processes are suggestive of neural tissue.

Notes: The male reproductive system of Artemia was studied by routine histological and histochemical techniques to demonstrate the general histology and distribution of proteins, carbohydrates, lipids, and alkaline and acid phosphatases.The System Consists Of Paired Testes, Vasa Deferentia, Accessory Glands, And Penes. The Testes Contain Germ Cells And Supporting Cells Throughout Their Entire Length. The Former Cells Are Located In Clusters And Undergo A Spermatogenic Maturation Which Is Similar To That Described For OtherAnimals. The Supporting Cells Seem Implicated In The Nourishment Of The Germ Cells. The Vas Deferens, Which Consists Of Secretory Epithelium Surrounded By Circular And Longitudinal Muscles, Secretes The Seminal Fluid, Containing A Neutral Mucopolysaccharide Or Mucoprotein, And Stores The Mature Sperm. The Accessory Gland Consists Of Approximately 20 Pairs Of Gland Cells, Each Pair Drained By A Neck Cell And Duct Cell Into The Collecting Duct. The Glandular Secretion, Mainly A Neutral Mucopolysaccharide Or Mucoprotein, Might Function As A Lubricant, A Copulatory Plug, Or An “Activator Substance” For The Sperm Or For Fertilization. Each Penis Consists Of A Non-Eversible Part And An Eversible Part Which Is A Tortuous Muscular Tube That Connects The Vas Deferens To The Outside.

Notes: Spermatozoa in the head of the epididymis of the flying squirrel have large cup-shaped acrosomal heads with two ventral ridges. The cytoplasmic droplet contains an ovoid body and a group of large granules. These structures may be related to the chromatoid body of spermatids. The spermatozoa form polarized cylindrical bodies with centrally placed tails and peripheral heads. The tips of acrosomes protrude into concavities of acrosomal cups of neighboring spermatozoa. Peripheral portions of acrosomes are in contact with microvilli (stereocilia) of epididymal cells. Polarized cylindrical bodies are present in five species of Sciuridae.

Notes: Groups of spermatids of Limulus polyphemus undergo differentiation in thin-walled cysts within the seminiferous tubules. The nucleus compacts to a spherical shape, but retains a much less condensed nuclear appendage, whose unique pores are each surrounded by a microtubule. The appendage, unmodified mitochondria, glycogen, and coated vesicles, all present in the mature spermatozoon, suggest an unusual degree of metabolic self-sufficiency of the cell.The acrosome is associated with a 50 μ-long acrosomal filament that penetrates the nucleus during spermiogenesis and coils up in the cytoplasm, enveloped by two outer nuclear membranes. The filament, which eventually comes to lie in the circumnuclear cisterna, retains a covering of one membrane during its discharge at the time of the acrosome reaction.The posterior region of the head forms a thin-walled collar with peculiar internal supports around the base of the flagellum. Serverance of intercellular bridges between spermatids, cytoplasm elimination, and rupture of the cyst precede liberation of the immature spermatozoa into the lumen of the seminiferous tubules.Notwithstanding its peculiarities, the Limulus spermatozoon, with its simple shape closely resembling that of annelids and molluscs, represents the most primitive arthropod spermatozoon congruent with the evolutionary stability of the xiphosurans.

Notes: Although there are a number of studies on tooth replacement patterns in lower vertebrates, most do not indicate whether this process is continuous throughout the year or is affected by either breeding or seasonal cycles. We have surveyed the replacement patterns found in living and specifically killed Necturus maculosus (Amphibia: Proteidae) to determine the nature of their variation throughout the year prior to investigating possible controlling mechanisms of the formation and eruption of amphibian teeth. Some animals (34), kept in a large outside tank, were killed at monthly intervals and their tooth-bearing bones radiographed using a modification of the technique previously described (Miller and Radnor, '70). Other animals (9), kept at 4°C, were anesthetized with tricaine methanesulphonate (M.S. 222), and wax impressions taken with beading (carding) wax of the functioning teeth at regular intervals. Animals examined in the late spring and summer (25) showed no signs of active tooth replacement. Small replacement teeth visible beneath each functioning tooth enlarged only slightly throughout the summer. In early and late fall some functioning teeth were lost and replacement teeth grew and erupted to replace them. Replacement patterns were very irregular and classical alternate form rarely seen. In a number of animals the replacement series was formed from every third tooth. Animals kept constantly at 4°C showed no replacement phenomena. Patterns varied between the different bones of the jaws and did not support the Zahnreihe concept of Edmund ('60).

Notes: The neural fat-body sheath surrounding the abdominal ventral nerve cord of Carausius morosus has been examined by light and electron microscopy. A perineural chamber between the ventral nerve cord and the sheath is present in the ganglionic regions, but in the interconnective regions the sheath directly covers the neural lamella. The sheath is differentiated into secretory cells with abundant granular endoplasmic reticulum and many mitochondria and storage cells with lipid droplets and granules presumed to be glycogen. The whole sheath is pervaded with tracheoblast cells and associated tracheal and tracheolar tubules. Recent evidence suggests that this sheath may have little power of ionic regulation. The function of the sheath, deduced from the fine structure described here, appears to be to serve the nutritional needs of the central nervous system. Why a sheath of this type appears to be confined to herbivorous insects with unusual haemolymph cationic balance is still unexplained.

Notes: Anatomical analysis of the forebrain and midbrain of Anelytropsis, Dibamus and feyliniids reveals structural similarities with those of skinks and snakes. Skinks and feyliniids are probably derived from a common ancestral stock. This is suggested by mutual reduction of several telencephalic nuclei, by similar trends in the development of the dorsal thalamus, and by similarities in the lamination of their optic tecta. Anelytropsis, Dibamus, feyliniids and snakes show interdigitation of the periventricular gray zones of the optic tectum and enlargement of lamina 7 of the posterior colliculus. Of these three taxa, Dibamus is most similar to burrowing snakes and many of its brain characters are intermediate between skinks and burrowing snakes. These similarities may suggest common ancestry between Dibamus and snakes rather than parallelism.

Notes: Serial sections of embryonic rat eyes were stained with hematoxylin and eosin, quantified (by counting pycnotic and viable nuclei), reproduced by camera lucida on wax plates, and moulded into reconstructions in order to study the normal progression of cellular death during morphogenesis. At least nine distinct necrotic loci (A through I) can be distinguished. Immediately following contact between the retina and surface ectoderm (day 11) degenerating cells were observed in (A) the ventral extent of the optic vesicle, beginning in the mid-retinal primordium and continuing ventrally in the optic stalk, (B) in the rostral optic stalk base, and (C) in the surface ectoderm encircling the early lens placode. No degeneration was observed in the dorsal half of the presumptive retina, in the entire pigment epithelium, or in the lens placode proper. During day 11.5 the lens placode thickens and forms a degenerating locus (D) in its ventral portion opposite the underlying pycnotic zone in the retina (A). During day 12 the ventral pycnotic zone (A) divides into two subunits (A1 and A2). Invagination of the lens displaces its marginal and ventral components (C and D) so that they come to occupy the lens pore area and presumptive corneal epithelium. Simultaneous invagination of the retinal rudiment juxtaposes the pigment epithelium which concurrently forms a necrotic area (E) adjacent ventrally to that in the retina (A1). Degeneration appears in the caudal optic stalk (I). The density of viable cells decreases adjacent to pycnotic areas in the retina and pigment epithelium and increases within these death centers. During day 13 the optic fissure forms within the subunits of the ventral pycnotic zone (A1 and A2). Degenerations are seen in the dorsal optic stalk (F) and in the walls of the optic fissure (G and H). Throughout these stages necrosis appears only in those portions of the eye rudiment where invagination is either retarded or completely absent.In part, these observations suggest that cell death serves (1) to retard or inhibit invagination within death centers, (2) to integrate the series of invaginations which mould the dorsal optic cup and optic fissure, (3) to assist formation of the pigment epithelium monolayer, and (4) to orient the lens vesicle within the eye cup. The spatio-temporal relationship between necrotic loci suggests that pycnotic cells in the retina may influence their production in the lens and pigment epithelium. Preliminary observations on the mouse, pig, and human substantiate those on the rat.

Notes: The functional anatomy of pulmonary ventilation in Thamnophis elegans was studied by electromyography. Flow of air into and out of the lungs follows a triphasic pattern and occurs while the glottis is held open by a dilator muscle. Non-ventilatory rest periods characterized by a closed glottis and lack of ventilatory movements occur between breaths. Exhalation is caused by contraction of a pair of dorsolateral sheets of muscle that extends from the ventral surface of the vertebral column to the medial surfaces of the ribs and a pair of ventro-lateral sheets that extends from the medial surfaces of the ribs to the mid-ventral skin. Inspiration is powered by contraction of a series of rib levators and retractors. The last phase of the ventilatory cycle is a passive expiration that may be caused by elastic recoil of the walls of the filled lungs and relaxation of muscles used during inspiration. The site of respiratory pumping is shifted craniad after large prey items have been completely ingested. The significance of this shift and its anatomical basis are considered.

Notes: Subcapsular cells lining the thymic stroma vary from low to high forms, while others have a hemocytoblastoid aspect. The purpose of the present study was to establish whether the transformation of the low forms into hemocytoblastoid subcapsular cells can be induced by an antigen. Rats given 10 Lf of diphtheria toxoid intramediastinally were killed at periods ranging from 3 to 24 hours later. Other rats were injected with 3H-thymidine at various intervals after the toxoid injection, and were killed one hour later. The observations revealed a rapid hemocytoblastoid transformation of subcapsular cells following administration of the toxoid. The transformation is detectable as early as three hours after the injection and can be completed after nine hours. Radioautography revealed that DNA duplication is initiated rapidly in the transforming subcapsular cells, since it can be completed 9 to 12 hours after the toxoid injection. Other observations suggested the transformation of reactive perithymic fibroblasts into subcapsular cells as well as the transformation of hemocytoblastoid fibroblasts and subcapsular cells into free hemocytoblastoid cells.

Notes: Non-innervated macrotrichia and microtrichia, thick-walled chemoreceptors and three kinds of thin-walled chemoreceptors are present on the antennal flagellum of Frenesia missa. One of the thin-walled receptors, the plate organ, is of a type not previously recorded for any insect. About four times as many plate organs are present on the flagellum of the male as on that of the female. They occur also on the maxillary and labial palps.

Notes: Electron microscope examination of the myofibrillar material in the avian latissimus dorsi anterior (tonic) and posterior (phasic) muscles revealed that the characteristic felderstruktur arrangement of the tonic muscle fibers develops during growth. Fibers of embryonic and young latissimus dorsi anterior muscles up to 87 days after hatching exhibited a fibrillenstruktur arrangement. Unlike the phasic muscle fibers in which the myofibril mass splits into discrete and regularly shaped myofibrils, the myofibrils in the tonic muscle become felderstruktur in appearance because of incomplete splitting of the myofibrils. The incomplete splitting of the myofibrils and the less extensive sarcoplasmic reticulum in the tonic muscle were related to its slower rate of tension development. The isometric contractile tension of the muscles was measured and it was found to increase considerably during growth. The tension increase was directly related to the increase in the fiber size, and the myofibril content. The rate of contraction of both the latissimus dorsi anterior and posterior muscles was found to increase very rapidly just prior to hatching. After hatching, the rate of contraction of the anterior muscle decreases differentiating into a tonic muscle at one month. The latissimus dorsi posterior muscle remains fast throughout development.

Notes: The antenna of fourth instar larvae of Aedes aegypti has one peg organ of a basiconic type innervated by four neurons. The dendrites are ensheathed to near their terminations at the peg tip by an electron-dense dendritic sheath and by a cuticular sheath. They have easy communication by diffusion with the external environment only at the tip through a peripheral ensheathing membrane and six slit-channels. One of the dendrites resembles a tubular body proximally and may be mechanoreceptive. The peg generally appears to be a contact chemoreceptor. There are three antennal hairs of a typical sensillum trichodeum type innervated at the base by one neuron each. An intricate terminal mechanism at the insertion of the dendrite in the hair is described. These are believed to be tactile hairs. There are also three antennal hairs each innervated by two neurons. The dendrite from one terminates at the base similar to that of a tactile hair, and is believed to function in a similar mechanoreceptive manner. The dendrite from the second neuron extends naked along the length of the hair lumen. It is believed to be primarily chemoreceptive, in a slow-acting general sensory function. In all the sensilla there appear to be secretions produced in the junction body regions of the dendrites, and there is evidence for accumulation of secretory materials in the dendritic tips in some of the sensilla.

Notes: The morphology of the retinal pigment epithelium and photoreceptor cells has been studied in the common newt Triturus viridescens dorsalis by light, conventional transmission and scanning electron microscopy.The pigment epithelium is formed by a single layer of low rectangular cells, separated by a multilayered membrane (Bruch's membrane) from the vessels of the choriocapillaris. The scleral border of the pigment epithelium is highly infolded and each epithelial cell contains smooth endoplasmic reticulum, myeloid bodies, mitochondria, lysosomes, phagosomes and an oval nucleus. Inner, pigment laden, epithelial processes surround the photoreceptor outer and inner segments.The three retinal photoreceptor types, rods, single cones and double cones, differ in both external and internal appearance. The newt, rod, outer segments appear denser than the cones in both light and electron micrographs, due to a greater number of rod lamellae per unit distance of outer segment and to the presence of electron dense intralamellar bands. The rod outer segments possess deep incisures in the lamellae while the cone lamellae lack incisures. Both rod and cone outer segments are supported by a peripheral array of dendritic processes containing longitudinal filaments which originate in the inner segment. The inner segment mitochondria, forming the rod ellipsoid, arelong and narrow while those in the cone are spherical to oval in shape. The inner segments of all three receptor cell types also contain a glycogen-filled paraboloid and a myoid region, just outside the nucleus, rich in both rough and smooth endoplasmic reticulum. The elongate, cylindrical nuclei differ in density. The rod nuclei are denser than those of the cones, contain clumped chromatin and usually extend further vitreally. Similarly, the cytoplasm of the rod synaptic terminal is denser than its cone counterpart and contains synaptic vesicles almost twice as large as those of the cones. Photoreceptor synapses in rods and cones are established by both superficial and invaginated contacts with bipolar or horizontal cells.

Notes: The ultrastructure of wing epidermis of the giant silkmoth, Hyalophora cecropia, was studied during pupal diapause and the first half of development to the adult. In diapause, the generalized epidermal cells are characterized by many free ribosomes, some vesicles and small lamellae of rough endoplasmic reticulum, some scattered short mitochondria and a few small Golgi complexes. During the early states of post-diapause development, before and after the time of apolysis (separation of the epidermis from the overlying cuticle), there is a marked increase in structures often associated with synthetic functions, such as polyribosomes, lamellate rough endoplasmic reticulum and Golgi complexes. On day five of post-apolysis development, just after the appearance of scale-forming and socket-forming cells, the generalized epidermal cells lay down the cuticulin layer of the adult cuticle. At this stage and later, the polyribosomes and lamellate rough endoplasmic reticulum decrease in abundance. Cell nuclei show three phases of temporary transition from predominantly lobed to predominantly round profile, which correspond to periods of reported DNA synthesis. Throughout this developmental process, therefore, there is good correlation of fine structure with changes in macromolecular synthesis recorded elsewhere.

Notes: In wings of the giant silkmoth, Hyalophora cecropia, scale-forming and socket-forming cells are first observed on day four of pharate adult development. Scale-forming cells appear synthetically active when they are first observed, for their basal region is filled with huge stacks of polyribosome-studed lamellate endoplasmic reticulum, numerous Golgi complexes containing secretory vesicles and many elongated mitochondria. During later development, some of these organelles diminish in number. Neck and scale regions are predominantly filled with longitudinally oriented microtubules and microfibril bundles, suggesting that their function is one of transport rather than synthesis. The scales originate as finger-like projections of the cell body. They subsequently elongate, flatten out and deposit a cuticle which has a surface differing somewhat from that in other lepidopterans. It consists of longitudinal ridges (1.8-2.4 μ apart), transverse ribs (0.6-1.0 μ apart) and microribs (0.10-0.13 μ apart).Socket-forming cells produce a socket around the neck region of each scale-forming cell. The socket differentiates into several morphologically distinct regions: an apical fibrillar region, a ribosomal region, a mitochondrial-microtubular region and a basal fibrillar region. The absence of polyribosome-studded lamellae of endoplasmic reticulum and Golgi complexes suggests that its primary function is not biosynthesis but support and protection of the scale.

Notes: Oogenesis in the anuran Xenopus laevis can be divided into six stages based on the anatomy of the developing oocyte. Stage I consists of small (50 to 100 μ) colorless oocytes whose cytoplasm is transparent. Their large nuclei and mitochondrial masses are clearly visible in the intact oocyte. Stage II oocytes range up to 450 μ in diameter, and appear white and opaque. Stage I and II are both previtellogenic. Pigment synthesis and yolk accumulation (vitellogenesis) begins during Stage III. Vitellogenesis continues through Stage IV (600 to 1000 μ), the oocytes grow rapidly, and the animal and vegetal hemispheres become differentiated. By Stage V (1000 to 1200 μ) the oocytes have nearly reached their maximum size and yolk accumulation gradually ceases. Stage VI oocytes are characterized by the appearance of an essentially unpigmented equatorial band. They range in size from 1200 to 1300 μ, are postivtellogenic and ready for ovulation. These stages of oocyte development have been correlated with physiological and biochemical data related to oogenesis in Xenopus.

Notes: The ultrastructure of the epidermis at different stages of the shedding cycle has been studied in Anolis carolinensis. Cells of the germinal layer are morphologically similar at all stages in the cycle. Immediately after leaving the germinal layer all daughter cells resemble one another closely. However, they later acquire specific ultrastructural features that enable them to be classified into six distinct fully differentiated types corresponding to the grouping previously set forth by light microscopy. A comparison of cytoplasmic filament size with the known X-ray diffraction data suggests that the Oberhautchen and β-layer contain a protein similar to that of avian feather; the protein in the α-layer and lacunar tissue is similar to that in mammalian hair, and the mesos layer cells probably contain a mixture of feather and hair-like proteins. The nature of the amorphous cytoplasmic material in the mature clear layer is as yet unknown.

Notes: Cleavage and blastoderm formation in Coelopa frigida are extremely rapid developmental processes. In short (6-7 minutes) successive cell cycles, nuclei multiply and spread out through the egg. The movement seems to be aided by endoplasmic vesicles and cisternae which are in direct contact with the nuclear membrane. The first cells to separate from the egg plasmodium in early superficial cleavage stages are the pole cells.Precursor material from multivesicular bodies forms the pole cell membranes. The primary nuclei from the posterior pole region are removed from the blastoderm by the pole cell segregation. Blastoderm nuclei from the regions adjacent to the posterior pole migrate into the residual periplasm after pole cell segregation has been completed and constitute the blastoderm nuclei in that region of the egg. Nucleoli are not revealed during internal cleavage. They appear in pole cells shortly after their segregation. The generation time of the blastoderm nuclei increases after the twelfth cleavage. Concurrently, nucleoli form in the blastoderm nuclei and permanent cell membranes separate individual blastoderm cells. After blastoderm cells have been separated from each other, they remain in contact with the interior yolk sac by means of cytoplasmic canals. This contact is maintained at least during the early phases of blastokinesis. Observations on nuclear migration and rapid membrane formation are discussed as examples of protein assembly from subunits as an alternative to de novo protein synthesis in early stages of development.

Notes: Twenty-three stages in the embryonic development of the western painted turtle, Chrysemys picta bellii are described. The staging is based primarily on morphological changes, as well as age and size of the embryo.

Notes: The dissected tooth bearing bones of 20 specimens of Amia calva (Pisces:Holostei) ranging from the third to tenth season have been examined radiographically and in alizarin red S stained and cleared specimens. Although forms of alternate (1:1) tooth series replacement (sensu Edmund, '60) were frequently observed, even in the youngest, immature specimens, many examples of irregular replacement were recorded. In several bones, the maxillae in particular, series with every third (2:1) or fourth (3:1) tooth replacing were seen and possible patterns of 2:2, were recorded. It is concluded that these data are not consistent with the Zahnreihen concept but support a morphogenic field concept of tooth development.

Notes: The description of the superficial veins of the face and neck was based upon the dissection of 28 male and female adult tufted or brown capuchin monkeys (Cebus apella), captured in southern Goiás, Brazil.Although the venous arrangement of these areas is basically the same in all primates, some characteristic differences were noted: 1. the anterior jugular and common facial veins were absent; 2. most specimens had a venous hyoid arch, and a connecting vessel between the external jugular and subclavian veins; 3. the inferior petrosal sinus drains into the external jugular v. through the postglenoid foramen; 4. the facial, lingual and cephalic veins open into the external jugular vein; 5. both the internal and external jugular veins have about the same diameter; 6. the vascular pattern appears to be quite stable; anatomical variations appear to be few and unimportant.

Notes: The ventral pelvic integument of anurans in hypervascular as compared to other skin regions. Recent studies indicate that this area is primarily responsible for water uptake and rehydration. Nine species representing four genera of terrestrial and aquatic Anura were dissected for comparison of vascularity in the pelvic area. Major differences in the ventral pelvic integumental vessels were found between aquatic and terrestrial genera. These variations are described, and names are suggested for previously unnamed vessels. Changes in vascularity are discussed and related to the literature on Anura pertinent to rehydration rates, tolerance of desiccation, resistance to desiccation, and habitat.Data from this study and previous studies suggest a correlation among the parameters discussed and habitat. The suggestion is made that when species are classified as xeric, mesic, or aquatic on the basis of the habitat in which they live, their responses to rehydration, tolerance to desiccation, and vasculatity should be considered, as these characteristics more accurately represent the micro-habitat.

Notes: In Esox americanus and Esox niger (Esocidae) there are two types of surface pits, sensory and nonsensory. Both types of pits are morphologically very similar and are associated with modified (cardioid) scales. The pits are distinguished by the presence and absence respectively of neuromasts. Ultrastructure of the neuromasts indicates that they are basically similar to previously described neuromasts. However, the hair cells have crystalline-like deposits in the nuclear region. The nonsensory pit contains a small group of distinct epidermal cells, called central cells. These cells occupy a central position in the pit, similar to that of the neuromasts in the sensory pit. The central cells are unlike any cell types described for fishes, and on an ultrastructural basis no function can be ascribed to them and the significance of the nonsensory pit is unknown.

Notes: Esox americanus and Esox niger (esocidae) possess two types of surface pits, sensory and nonsensory. The pits are morphologically very similar and both are associated with modified (cardioid) scales. The pits are distinguished by neuromasts in the sensory and central cells in the nonsensory pit.Neuromasts and central cells are responsible for the formation and maintenance of respectively the pit and cardioid scale. This supports an extension of the epidermal co-participation hypothesis that epidermal cells control the form of dermal structures in addition to contributing to composition.The central cells are similar in structure to induced primordial cells of regenerating neuromasts.The development of primordial cells may be arrested and the cells maintained in a static condition during which time they still influence the dermal tissues and maintain a pit and cardioid scale. Essentially this represents the experimental conversion of a sensory pit into a nonsensory pit. This evidence is taken in support of the hypothesis that the nonsensory pit and central cells represent an aplasic condition of the lateral line system.

Notes: The mutant gene srn produces sireniform abnormalities in the mouse. The effects of this gene on normal prenatal development were examined histologically by retrograde analysis from day 10 through day 18 of gestation.The sireniformphenotype is characterized by the fusion of the hindlimbs and accompanying defects of the posterior appendicular skeleton. Visceral defects involve the urogenital system and the lower intestinal tract. A single umbilical artery arises from the dorsal aorta and controls the fetal circulatory pathway normally mediated by the lateral umbilical arteries. This artery is believed to have resulted from the fusion of the paired primitive umbilical arteries.It is suggested that the srn mutation causes a narrowing of the posterior amnion early in development. The resulting abnormal pressure causes a dorsal displacement of the hindgut, allowing fusion of the hindlimb buds. Abnormal structural relationships and pressure in the narrowed posteriior region disrupt normal urogenital and intestinal development and increase the proximity of the primitive umbilical arteries.

Notes: An anatomical analysis of the chicken trigeminal ganglion was made using light microscopy on specimens prepared by usual chemical fixation or freeze-drying methods and by electron microscopy. Two types of neurons were consistently seen, dark and light cells. Dark cells contained a dense cytoplasm with Nissl substance distributed evenly throughout, whereas light cells had a less dense cytoplasm containing clumps of Nissl substance. The Nissl bodies in light cells contained only a few small cisternae of granular endoplasmic reticulum as compared with many stacked cisternae in Nissl bodies of dark cells. The ratio of dark to light cells was approximately 62:38 in all regions of the ganglion. Dark cells were consistently smaller than light cells. In the seven-day old chick, the mean diameters of the dark and light neurons were 21.4 μ and 29.5 μ respectively; in the adult the values were 29.9 μ and 39.7 μ respectively. It is concluded that the dark and light cells belong to two distinct neuronal cell populations.

Notes: A morphological study of the developing chick trigeminal ganglion was done. For descriptive convenience, four stages of development have been defined: Phase I (2 to 4 days of incubation)  -  Both the neural crest and epidermal placode contribute to the forming trigeminal ganglion, which is comprised of clusters of undifferentiated cells and primitive neuroblasts. Toward the end of this phase, satellite cells and unmyelinated nerve fibers are seen. Phase II (5 to 10 days of incubation)  -  In the lateral portion of the ganglion, large differentiating neuroblasts and young bipolar and pseudounipolar neurons were present. The latter were characterized by a large, eccentrically located nucleus at one pole, a long axonal process at the opposite pole, and a clear centrosphere region between the two. In the medial region of the ganglion, most of the neurons were smaller and more closely packed together. Phase III (11 to 17 days of incubation)  -  The ganglion was constituted of bipolar and pseudounipolar cells with an apparently random distribution of small and large neurons. Nissl bodies appeared in developing neurons. Phase IV (18 days of incubation to 3 weeks post-hatching)  -  Light and dark neurons first made their appearance. Dark neurons were characterized by (1) clear perinuclear cytoplasm containing a Golgi apparatus, vesicles and mitochondria and (2) a peripheral cytoplasm of densely packed stacks of Nissl substance. Light neurons contained individual clumps of Nissl substance distributed in a pale cytoplasmic matrix.

Notes: Histological studies of the neurosecretory system during the postembryonic development of a spider, Argiope aurantia, were made at the light-microscopic level.Neurosecretory cells which are found in all stages are classified into type I and type II cells. The type I cells are present in the aboral region of the brain and in pedipalpal, ambulatory and abdominal ganglia of the subesophageal mass. The type II cells which appear from the seventh stage are confined to the cheliceral ganglia. Three stages of secretory activity (poor, medium and full) based on stainability are described in these cells.In both types clear axonal transportation of neurosecretory material is observed. The discrete tracts and commissures formed by these neurosecretory axons are described in the brain and subesophageal ganglion. The complexity of some of these pathways is comparable to that of the ordinary neurons.One pair of nerves from the brain and four pairs of nerves from the subesophageal mass enter a neurohaemal organ, the Tropfenkomplex. This is a paired structure, situated dorsally, on either side of the subesophageal mass. The neurosecretory axons branch extensively within the organ and on their course they from sacs or pools filled with secretory material.The Tropfenkomplex is enveloped by a thin neural sheath which runs deep into the organ dividing it into a series of lobes. Glial cells are distributed within the organ. As in the neurosecretory cells, changes in stainability of secretory material were also observed in the Tropfenkomplex.During intermolt periods two peaks of stainability have been noticed. The first peak lasts for 24 hours after the molt, and this is followed by a low activity period between second and fifth day. From the sixth to the tenth day after the molt the second peak commences. It is suggested that the second peak may be responsible for bringing about molting.The cheliceral group appears (seventh stage) at a time when external indication of reproductive characters are visible. In the ninth stage, by the tenth day after the last molt, several of the type I and type II cells contain much secretion. This is followed by maturation of gonads and oviposition. Thus both type I and type II cells are believed to be involved in the reproduction of the animal.

Notes: A cinematographic analysis of the unrestrained walking, trotting, galloping, jumping and landing movements of 11 adult cats was undertaken to provide previously unavailable information concerning the demands imposed on the nervous system for the control of low and high speed movements and the demands imposed by such natural movements on muscle performance and proprioceptive response.With due regard for the swing (F and E1) and stance (E2 and E3) phases of the step cycle of an individual limb, single frame analysis of the film permitted measurement of instantaneous angles of the lower spine, hip, knee, ankle and metatarsophalangeal joints. Appropriate lever arm measurements were also made on 50 freshly dispatched cats and 25 cadavers such that the Law of Cosines could be used to calculate instantaneous lengths of select hind limb muscles that would apply to the natural movements of adult cats of small (1.5-2.5 Kg), intermediate (2.6-3.5 Kg) and large (3.6-4.5 Kg) size. Muscle displacements were analyzed relative to maximum and minimus in situ lengths and the lengths associated with quiet standing. Use was also made of a previous electromyographic analysis of hind limb muscles during unrestrained locomotion (Engberg and Lundberg, '69).The sequential relations between the four phases of the step cycle are maintained as forward speed increases from walking ( 〈 2 mph) to high speed galloping ( 〉 16 mph). There are significant differences in the time consumed by each phase, however, with a greater reduction in the E3 phase, little reduction in the E2 and E1 phases and virtually no reduction in the F phase. When each phase is expressed as a relative percentage of the duration of the total step cycle, the greatest reduction is again in E3 with little change in the E2 phase. In contrast F and E1 phases increase in the percent of time they occur in each cycle, with the greatest increase in the F phase. For all speeds, analysis of the phase relations between movements of various sections of the hind limb revealed a remarkable unity of knee and ankle joint movement. The hip joint is largely out of phase with the knee and ankle during E1 and E2, all three joints being in phase in F and E3. The digits are essentially out of phase with the other joints except in the stance phase of the gallop.Rates and extents of muscle displacement during natural movements are greater than might be anticipated when expressed in absolute mm's and mm/sec but not when considered in relation to maximum and minimum in situ length and the length associated with quiet standing (Ls). During stepping a progressive increase in forward speed results in: (a) a greater usage of muscles at lengths between Ls and maximum in situ length; (b) for knee and ankle extensors, pronounced increase in the lengthening contraction associated with the E2 (yield) phase of step; and, (c) for both flexor and extensor muscles, an increased active phase of lengthening or near isometric contraction immediately prior to periods of active shortening. In contrast to these changes in active muscle status, the change from walking to galloping has little effect on the extent and rate of passive muscle displacements, particularly the F phase stretch of extensors.For the soleus muscle, calculations were made of the relation between changes in overall muscle length during natural movements and the length of the average muscle fiber and the tendon of insertion. These measurements revealed that the increases in fiber length when passive and decreases in length during active shortening are less than would be anticipated from the extensive liteature on extirpated fibers. In contrast, the increase in fiber length when active is greater than would be expected from the admittedly sparse literature on this subject.The results of this study are discussed largely in relation to two points of neurophysiological interest: the physiological range of muscle stretch as it pertains to the responsiveness of muscle spindles and tendon organs; and those mechanical aspects of lengthening contractions that give insight into the neural control of stepping. For exciting both spindles and tendon organs passive muscle stretch and shortening contractions are shown to be relatively ineffective and lengthening and isometric contractions particularly effective movements. It is suggested that, just as recent literature has emphasized the co-activation of efferent alpha and gamma motoneurons as a muscle becomes active, so too is there a synchronous activation of afferents, particularly the Ia and group II endings of muscle spindles and Ib endings of tendon organs. Finally the thesis is advanced that, while it has been convenient to separate E2 from E3 in the description of the stance phase of the step cycle, extensor muscles are actually undergoing a single mechanical event: an active stretch-shorten cycle for knee and ankle extensors and an active isometric-shorten cycle for hip extensors. This hypothesis has significant implications for the neural control program that regulates the stepping sequence in that it emphasizes the extent to which appropriate changes must be preprogrammed in the mechanical properties of muscles for the smooth execution of stepping.

Notes: Ovaries of the giant silkmoth Samia cynthia Drury have been studied histologically and histochemically during diapause, adult development, and after injury to the diapause animal. In addition to cellular changes involved in follicular growth and vitellogenesis, changes in the intermediate layer cells are very striking, showing a distinct pattern during ovarian development and after injury. Two types of granules, one periodic acid-Schiff (PAS) positive, the other paraldehyde-fuchsin (PF) positive, change in their number and distribution in the intermediate cells during development and after injury. The PAS-positive granules appear during the first one-third of development, increase in number and size until the tenth day, then gradually dwindle in number and size, and disappear in the adult cells. The PF-positive granules, present in moderate numbers in the diapause animal, decrease in number until the tenth day of adult development, then reappear, and are present again in adult intermediate cells. After injury to a diapause pupa, intermediate cells show a greatly increased number of PF-positive granules, but none that are PAS-positive.The PAS-positive granules are a neutral or mildly acidic mucosubstance, and may correspond to lysosomal activity, while the PF-positive granules may be a neurosecretory-like substance or the product of hormone-dependent protein synthesis, since the patterns of granule distribution in the intermediate cells seem to reflect both general metabolic and hormone-related events.

Notes: The cranial glands of ten species of turtles were studied by the use of histochemistry applied to serial sections of whole heads. The majority were stenohaline species, but one brackish water form, Malaclemys, was included. The results show that all species have two major orbital glands, an anterior Harderian gland, and a posterior lachrymal gland. The latter is seromucous in all species except Malaclemys terrapin in which the gland shows little evidence or organic secretion. External and medial nasal glands are found in all species studied, and also are seromucous glands. With these reslts, combined with a review of the literature the following conclusions are made. The Harderian gland is by definition the orbital gland opening through the medial surface of the nictitating membrane at or near the anterior canthus. It is of constant occurrence, and histological appearance, probably serving the same function. However, despite much recent study this function remains unknown. The lachrymal gland is defined as the orbital gland which opens through the lateral surface of the nictitating membrane, or medial surface of the lower eyelid, at or near the posterior canthus. It is of variable occurrence, absent in many reptiles, and has a histological structure which is also variable. In the stenohaline species it is apparently involved in organic secretion, while in the brackish water Malaclemys it may be involved in salt secretion, as it is in Cheloniidae. The nasal glands in turtles are probably homologous with the nasal salt glands of lizards and birds, but they do not appear to subserve the same function. In all species of turtles studied the nasal glands are seromucous. They are perhaps involved in the maintenance of the epithelium of the olfactory cavity.

Notes: The dorsal proctodeal wall of the Coturnix contains a gland which is especially well-developed in the sexually active male and which secretes a foamy exudate. This gland has not been recorded in any other genus of birds and appears to be unique to members of the genus Coturnix. On the basis of its location in the adult we have named this gland the proctodeal gland (glandula proctodealis). Structure of the gland does not conform to any curently defined category of glands because it is an aggregate of individual glandular units each of which opens independently into the proctodeal cavity but with the entire structure enclosed by a connective tissue capsule. We have thus characterized it as an aggregate gland. Observations on the arrangement and composition of the fibrous capsule and its intimate relationship to the perimysium of M. sphincter cloacae indicate that release of the secretion probably results from contraction of the cloacal musculature. Preliminary data suggest that development of glandular tissue in the female may be a function of age rather than of androgen sensitivity which characterizes the male gland. It is concluded that the chemical nature of the glandular secretion and its function in the sexually active bird, as based on presently available information, remains unknown.

Notes: Wound healing in the integument of the sea cucumber, Thyone briareus, was studied for up to 50 days after inflicting wide excisional wounds and for 14 days after producing incisional wounds. Rapid re-epithelialization of the wound was effected by the migration of epidermal cells and pigment cells from the periphery of the wound margin. This occurred without apparent evidence of concomitant mitotic activity. Dermal wound healing was completed by the fourteenth day in the incision wounds but occurred very slowly in the broad excision wounds. Morula cells seem to be involved in both epidermal and dermal wound healing, although their precise role is unknown. In excisional wounds the integument was never completely restored to its normal appearance during 50 days of observation.

Notes: The spleen of the adult gerbil (M. unguiculatus) is characterized by the absence of venous sinuses and ellipsoid sheaths. The follicle (white pulp) is separated from the surrounding red pulp by a distinct marginal zone. The cell types in the marginal zone are common to both the follicle and red pulp. Separating the marginal zone from the follicle is a vascular channel of capillary dimension, the marginal sinus. A number of terminal segments of the arterial vessels within the follicle were observed to form a direct connection with the marginal sinus. Ultrastructurally, discontinuities were evident within the walls of the marginal sinus that would permit passage of both cellular and plasma components from the marginal sinus to either marginal zone or the follicle.

Notes: The electron microscopy of the epiphysis cerebri of the antarctic seal Leptonychotes weddelli revealed a highly organized organ. The general cytological characteristics of the pinealocytes and the glial cells are described. The capillary blood vessels are the nonfenestrated type. The organ is richly innervated by mainly unmyelinated nerve fibers. Most of the axons end in the inner part of the organ, around vessels, some of them in relation with pinealocytes. The significance of the findings is discussed.

Notes: Extraocular muscles from representative species of vertebrate groups ranging from amphibians to the higher mammals were examined in serial histological sections for the presence of muscle spindles. These observations and data from the literature indicate that extraocular muscles of the pig, calf, sheep and other even-toed ungulates are richly supplied with well-defined spindles having a generous complement of intrafusal fibers distinguishable as nuclear bag and chain fibers. Spindles in human eye muscles are also numerous. In macaque and chimpanzee muscles a few poorly developed spindles were present in some, but not all, muscles. No encapsulated receptors were found in 20 other mammalian and submammalian species examined in this study. When present, spindles tended to be located in the zone of small muscle fibers found along the orbital surface of the muscle. Rectus and oblique muscles in all species had such a zone, so that its existence did not determine whether spindles would occur.