ALBERT

Notes: The retinofugal projections of the snake Thamnophis sirtalis were studied by the method of experimentally induced Wallerian degeneration stained by the Fink-Heimer method. The retinal ganglion cells project to all parts of the contralateral lateral geniculate complex, nucleus lentiformis mesencephali, nucleus geniculatus pretectalis, nucleus posterodorsalis, basal optic nucleus and superficial layers of the optic tectum. In addition, the retinofugal projections were observed terminating in portions of the ipsilateral lateral geniculate complex and nucleus posterodorsalis.Examination of the morphology of the retinal terminal areas stained for Nissl substance with cresyl violet led to the conclusion that these regions are well differentiated and should not be considered poorly developed when compared with other reptilian forms such as turtles.

Notes: The course of the statoblast formation in Pectinatella gelatinosa was divided into four stages and studied histologically and histochemically. The bottom of the cystigenous cup is a center of cystigenous cell differentiation and the peripheral zone of the inner cystigenous layer turns to the outer cystigenous layer as the cystigenous cup grows. The annulus is formed by migration and transformation of the outer cystigenous cells.During early stages, the yolk cells have an intensely pyroninophilic or RNA-rich cytoplasm. The cytoplasmic pyroninophilia then diminishes as the amount of yolk granules increases.Several kinds of yolk substances occur in the mature statoblast. During statoblast formation glycogen appears first, then glycoprotein and finally neutral unsaturated lipid.Acid phosphatase activity is associated with granular structures in the cytoplasm. In the cystigenous vesicle, acid phosphatase activity is low and confined to the apical extremity of the cell. Histochemically detectable alkaline phosphatase activity is not involved in the formation of the statoblast.

Notes: The anatomy and physiology of feeding in miniature swine were studied, using gross dissection, electromyography, cinematography, and cineradiography.Small particles are preferred for ingestion, and large items are usually broken down outside of the oral cavity. The particles are initially picked up with the lower lip and then retrieved by the tongue; the tongue very rarely leaves the oral cavity. Geniohyoid, mylohyoid and digastric are the most active muscles during food collection.Mastication is fairly rapid (3 cycles/sec) and involves a transverse component which may be either medially or laterally directed. The direction of motion is generally reversed with every chew. Electromyography indicates that the transverse rotation is caused by a force couple consisting of protrusors (masseter, medial and lateral pterygoids) on one side and retrusors (zygomaticomandibularis and temporalis) on the other. The direction of the rotation is not necessarily related to the side containing the bolus. Mandibular depression is electromyographically biphasic. Concurrent tongue and hyoid movements complicate the interpretation of activity patterns in the oral floor.Both masticated food and liquid are stored between the tongue and the soft palate and epiglottis before being swallowed. Swallowing involves very strong activity in all of the hyoid and tongue muscles and very low activity in the adductors. Liquid is taken in by suction rather than lapping.Comparisons with other mammals are presented.

Notes: The wall of the gametolytic gland in Aplysia and Phyllaplysia consists of a muscular layer lined with an epithelium incorporating four distinct cell types, some of which show intense secretory activity. The cytoplasm of these cells, rich in RNA, has a peripheral layer of densely-packed mitochondria in association with a smooth endoplasmic reticulum. Lipid globules, perhaps resulting from absorption of lumen contents by microvilli, appear in the cytoplasm in the course of growth and reproductive activity. A basal band of fibrillar material appears to serve as a cytoplasmic skeleton. The elaboration of cell types, extensive areas of cytoplasmic RNA, and vigorous secretory activity suggest important roles for this organ such as development of food reserves, recycling of sexual materials of high physiological value, and interaction with the bag cells of the nervous system in coordinating ovulation with the availability of capacitated, exogenous sperm.

Notes: The predaceous neotropical characoid fish Ctenolucius has an essentially homodont dentition, the number of teeth increasing linearly with age. The basic manner of tooth replacement suggests that Ctenolucius is a primitive characoid. Tooth replacement continues throughout life and is similar to that of tetrapods, involving replacement waves which pass from the back to the front of the jaws. The waves containing the greatest number of teeth are found just anterior to the middle of the jaws. In the upper jaw the increase in the number of teeth is restricted to the anterior portion (premaxillary) whereas the number on the posterior part (maxillary) remains constant. In specimens measuring from 68-230 mm in standard length the posterior portion of the upper jaw doubles in length whereas the anterior portion triples. It is suggested that the area immediately anterior to the middle of the jaw, where replacement waves are longest, is where most of the increase in tooth numbers occurs.During growth of the teeth the absolute height is always greater than the absolute width as the shape changes. The final shape of the recurved conical teeth is determined only in the last stages of tooth formation when the main axis of growth abruptly changes.

Notes: Improved histological procedures have revealed in some detail the form and structure of auditory receptor organs in the frog. These organs, the papilla amphibiorum and papilla basilaris, are located in extensions of the saccular cavity, and lie in a path of vibratory fluid motion beginning at the columellar footplate and extending in a continuous circuit through the perilymph spaces and the round window back to the middle ear region.These organs exhibit great uniformity, and for the amphibian papilla there is a high degree of complexity in the tectorial structures that overlay the ciliated ends of the hair cells. In both papillae a “sensing membrane,” which is a derivative of the tectorial body, lies in the path of fluid flow and aids in the stimulation process.The mode of stimulation of the hair cells in the amphibian ear is peculiar, and in principle is the reverse of the familiar one of reptiles, birds, and mammals.

Notes: To determine the prism sheath configurations in human cuspal enamel 80 teeth were initially ground to produce flat surfaces through the following planes: a horizontal series at successively greater distances from the dentinoenamel junction and longitudinally through the center of the cusps. Individual teeth were suspended in an acid-alcohol solution (1 cm3 conc. HCl in 100 cm3 95% ethanol) at 37°C for seven to ten days. The treatment “softened” the enamel to a depth of approximately 1 mm. The teeth were embedded in Epon and sectioned at 0.5 to 10 μm with a diamond knife. Thick and thin ground sections for phase contrast microscopy and acid-etched ground sections for Nomarski differential interference microscopy were prepared through the same regions. In thicker longitudinal sections, the prisms in gnarled enamel formed a zig-zag pattern which was unlike the twisting pattern generally observed in ground sections. The thinnest transverse sections showed the sheath outlines to be dramatically different from those seen elsewhere in the enamel. Some prism sheaths were circular, others were in the form of spirals. What could be described as sheaths within sheaths were also seen. In the thinnest longitudinal sections the prisms were seen to be elongated and discontinuous. Sheath outlines in enamel adjacent to the central core of gnarled enamel were similar to those described elsewhere in the body of the enamel. Keyhole, modified keyhole patterns and arcade forms were the dominant sheath patterns. Other atypical sheath configurations were seen scattered throughout this region.

Notes: The differentiation and degeneration of the cement gland in Xenopus laevis is described. The gland is first observed histologically at stage 19 (neural tube stage) as a packed group of apical ectoderm cells heavily laden with oocyte pigment granules, lying ventral to the cranial neural fold. By tailbud stage 35/36, the gland cells have increased in height and are approximately ten times taller than nonglandular apical ectoderm cells. The nuclei divide the gland cells into an apical region that is eosinophilic and contains oocyte pigment granules, and a basal region that contains clear droplets. The cells are decreasing in height by stage 40 (early tadpole) and begin to lose their pigment granules. Between stages 45 and 48, the pigment is extruded and the clear basal droplets diminish in number. From stage 48 to 49 the cells become vacuolated and the histotypic characteristics of the functional gland are lost. The gland is not vascularized, nor do phagocytic cells appear in its vicinity during any stage of its development. It remains bordered at its base by subjacent basal ectoderm during its entire life cycle of 10 to 12 days at room temperature.

Notes: The fiber constituents and connections of the calyces  -  the input-receiving regions  -  of the corpora pedunculata (“mushroom bodies”) were studied in reduced silver preparations from the American cockroach, Periplaneta americana (L.). In the outer synaptic layer of the calyces five fiber classes were distinguished, the first three of which arise outside the mushroom body. (1) Four highly similar neurons with somata near the optic lobe branch into different parts of the ipsiateral protocerebrum, including both calyces. Their fibers are highly constant in arrangement and position and contain small nucleus-like bodies. (2) The tractus olfactorio-globularis (sensu lato) emits fiber groups which course along the calycal walls as “calycal tracts” before ultimately dissipating into the synaptic layer. Variability within these tracts is described. (3) Fibers of undertermined origin outside the mushroom body radiate from the calycal center outwards through the synaptic layer. (4) From the inner calycal layer of neurites belonging to intrinsic mushroom-body neurons, perpendicular collaterals enter the synaptic layer. (5) Intrinsic-neuron somata near the calycal rim emit fibers which course tangentially within the synaptic layer from calycal rim to center. These fibers form a special peripheral zone in the pedunculus.The predominant presumably afferent calycal fiber class is that derived from the tractus olfactorio-globularis. No evidence was found for tracts from optic lobe to calyces. On this basis, and in light of the experimental and comparative anatomical literature, it is suggested that the corpora pedunculata of P. americana and other pterygotes are fundamentally second-order antennal sensory processing centers.Conflicting observations in earlier reports are critically discussed.

Notes: The skin of Bagarius bagarius (Ham.) is devoid of scales but is rough due to the presence of numerous pentagonal epidermal elevations, which are separated by deep furrows at regular intervals. These elevated pentagonal regions of the epidermis are covered by dead cornified cells in the form of caps. As the old cap goes off a new one is formed by the death of the underlying epidermal cells. The middle layer of the epidermis is mainly composed of well defined polygonal cells. Their cytoplasm is granular in nature and give reactions for protein bound sulphydryl groups. The stratum germinativum is composed of two types of basal cells, the columnar cells and the spherical cells.The flask shaped mucous glands are restricted to the epidermal furrows and secrete either neutral or acidic mucopolysaccharides. Certain large specialysed granular cells are found in the epidermis which are grouped around the taste buds. These specialysed cells may be the photocytes.Two layers of the dermis can be distinguished - the relatively thin stratum laxum and the thick stratum compactum. Dermal papillae mainly support the taste buds. The pigment cells are arranged in two layers in the dermis.The subcutis is composed of loose connective tissues, richly infiltrated with the fat cells, nerves and blood capillaries.

Notes: In further consideration of the lizard ear, the fine structure of the cochlea has been investigated and related to auditory sensitivity in members of the family Cordylidae. The ear of this group of lizards is unusual in that a tectorial membrane is present only in a modified and seemingly vestigial form, and this membrane makes no connections with the auditory hair cells. These cells are provided instead with a series of sallets, small bodies extending in a single row through the dorsal and middle regions of the cochlea, where they rest upon the tips of the ciliary tufts and evidently bring about a stimulation of the hair cells because of their inertia. At the ventral end of the cochlea this line of sallets ends, and here is a single, relatively enormous structure, the culmen papillae, that serves a similar purpose for a large group of hair cells. Consideration is given to the manner of stimulation of the auditory sense cells in these species in relation to others with the usual arrangements involving connections between the ciliary tufts and a tectorial membrane.Included also is a study of a species of Gerrhosaurus, which some have included in the cordylid family and others have placed in a family of its own. The cochlear structure in this species is similar to that of the cordylids in many respects but differs in the ventral region, where instead of the culmen there is a heavy tectorial plate, similarly covering a large number of hair cells but connected to a tectorial membrane.The functioning of these ears is assessed in terms of the cochlear potentials, and is found to vary with species from better than average to excellent in comparison with other lizards investigated. The structural differentiation also is of fairly high degree, and hence it appears that ears without tectorial connections, or with such connections only in a limited region of the cochlea, can perform in a highly serviceable manner.

Notes: The black carpet beetle, Attagenus megatoma (Fab.), has been reported to exhibit negative phototaxis immediately after emergence. In later adult life, after the period during which most oviposition has occurred, the beetles are found to be photopositive. The compound eyes of one-day-old (Post-emergence) and nine-day-old (Post-ovipositional) female beetles were studied by electron microscopy and a number of strong differences were found between eyes at the two ages. The corneal facets of one-day eyes had the form of convex-concave lenses, while those of nine-day beetles were double-convex lenses. The primary and secondary pigment cells of young eyes were large and contained much endoplasmic reticulum and little accessory pigment. In the older eyes the pigment cells were reduced and contained much pigment, the proportion of endoplasmic reticulum being greatly reduced by comparison with the one-day eye. The cross-sectional area of the rhabdom was greater in the older eye.The possible relationships between age-related changes in eye morphology and behavioral changes during the same period are discussed.

Notes: A seasonal study of the seminal vesicles in relation to that of the testes had been conducted in the catfish, H. fossilis. The annual reproductive cycle of the catfish has been divided into (i) Preparatory period (February-April), (ii) Prespawning period (May-June), (iii) Spawning period (July-August) and (iv) Postspawning period (September-January). Testes exhibit initiation of spermatogenesis in the mid-preparatory period, but significant increase in weight of the testes accompanied by active spermatogenesis occurs during the prespawning period. In the spawning period, the testes are maximally enlarged and their seminiferous tubules are packed with spermatozoa. Following spawning, the testes gradually regress in the postspawning period. The seminal vesicles show initiation of secretory activity during the preparatory period but their recrudescence lags behind that of the testes by about a month. The seminal vesicles attain maximum weight and secretory activity during the spawning period. Thereafter, the seminal vesicles regress precipitously and sooner than the testes.The histochemical and biochemical studies on the seminal vesicles indicate that the secretion contains mucoproteins, acid mucopolysaccharides, primary proteoses, besides traces of phospholipids and native proteins.

Notes: During cleavage of honeybee eggs two peaks arise in the longitudinal distribution pattern of the periplasm which coincide with the site of the differentiation center and the site of a mesodermal center. A very similar pattern is exhibited by the dorsal plasmstrip, a narrow band of thicker periplasm which is formed during cleavage along the dorsal midline of the egg. The present paper describes the development of the dorsal plasmstrips of two inbred strains of honeybees during early cleavage stages. Differences between the two strains reside in the total size of their dorsal plasmstrips and in the timing of the formation of the anterior peak which coincides with the site of the differentiation center. The bearing of these findings upon embryological studies is discussed.

Notes: The “cuticle,” which revests the starfish tube foot, has been studied by electron microscopy and the findings correlated with histochemical observations.The “cuticle” is composed by two distinct zones; an outer zone including numerous microvilli, which extend from the inner zone into and through a fibrillar substance distinctly organized in two layers. These microvilli protrude slightly beyond the outer surface, where their tips give rise tonumerous extremely delicate fibrils. The second inner zone, of quite variable thickness and condensation of material, presents a coarser fibrous matrix where organelles and inclusions can be found.The whole cuticular complex does not derive from the majority of the epithelial cells, but is probably an extension of a special kind of T-shaped cells appearing at intervals, the “cuticle” forming a syncytial surface.Histochemical investigations indicate that the “cuticle” contains a combination of neutral and acid mucopolysaccharide, with a marked neutral predominance, the outer one displaying also an extremely thin coat of acid mucopolysaccharide with the sulfate group.The ordered arrangement of the microvilli suggests that this situation is imposed by the strong bond existing between the microvilli and the ouble mucopolysaccharide layers which would act as a cementing substance stabilizing the entire apical surface of the cell.

Notes: The length of the oviduct, the thickness of its wall, and the height of its mucosal epithelium and cilia were measured in (a) 0-, 2-, 4- and six-month-old rabbits, (b) rabbits ovariectomized at birth and (c) ovariectomized, estrogen-treated rabbits. The length and external diameter of the oviduct increased progressively until four months of age, after which their rates of increase declined. The thickness of the oviductal wall at the uterotubal junction was twice as large as that of the isthmus at two months of age and six times as large at four and six months of age. The height of the mucosal epithelium in the fimbriae was less than that in other oviductal segments at birth, but exceeded that in other segments at six months of age. Ciliated cells and motile cilia were absent 24 hours after birth; they were first observed two months after birth. The cilia of fimbriae were shorter than cilia elsewhere in the oviduct. Neonatal ovariectomy retarded the development of the oviduct and the mesotubarium and caused pyknosis of ciliated and non-ciliated cells of the oviductal mucosa. Cells with scarcely motile cilia were present five and one-half months after neonatal ovariectomy.

Notes: In continuing study of gene and genome interaction as a possible etiological mechanism in normal and abnormal growth and malformation, the ventral spinous processes (VSPs, crural insertions of the diaphragm) were used as additional epigenetic variants to portray differences in the basic gradient growth pattern. Over 700 comparisons of mean differences in number (range or magnitude) and peak (position) of the VSP gradient, in the same populations of strains III, DA, and IIIDa (into which the Da gene had been introduced from strain DA), provided populations of +/+, Da/+ and Da/Da on two different genome backgrounds. They reveal the individual effects on the VSPs of underlying growth processes associated with the Da gene dosage, vertebral border shifts and stillbirths. Both Da and stillbirths demonstrate growth influences which interact additively to reduce the range and shift the peak anteriorly in opposition to those of the border shifts. The growth effects induced by border shifts are in some cases significantly so much greater as to seemingly inhibit or even reverse either the specific gene Da or stillbirth effects. The way that interaction of such growth influences can enhance, suppress or cancel each other and the relation to specific growth gradients and functions is of particular importance to understanding the etiology and growth mechanisms of spontaneous and unexpected exogenously or endogenously induced malformations in non-isogenic stocks.

Notes: The epidermis of 146 specimens of Dipsosaurus dorsalis and 182 Uma notata collected throughout the active period of the animals' year has been examined. The morphology of the epidermis is essentially similar to previously described lacertilians but differs in the relatively great degree of development of the mesos layer and the complete keratinization of the lacunar tissue prior to sloughing.Analysis of sloughing frequency throughout the year suggests that species specific patterns may exist, but these do not correlate with any particular known ecologic datum. The patterns do not reflect the reproductive activity of the two species supporting previous experimental conclusions on the lack of effect of gonadial hormones on epidermal activity.There appears to be no evidence of association of femoral gland activity with epidermal activity in D. dorsalis, but the situation is not clearcut in U. notata. These data are discussed in the light of recent studies of the evolutionary origin of epidermal glands in lizards.

Notes: The structural changes of mitochondria that occur during oogenesis and early embryogenesis in the rabbit have been examined with the electron microscope. Mitochondria of oogonia are both elongate and oval and contain a variable number of cristae which may or may not traverse the longitudinal axis of the organelle. When oogonia differentiate into oocytes, mitochondria become spheroidal and their cristae are sparse when compared with those found in the ellipsoidal organelles of concomitantly maturing follicle cells. As differentiation proceeds, the cristae of the mitochondria display varied configurations. For example, many display an arch-like arrangement in several regions of the organelle whereas others contain a pair of concentric membranes closely associated with limiting membrane of the mitochondrion.Mitochondria of stages from the fertilized egg to the morula possess the same internal structure as those of young oocytes. As the morula differentiates into a blastocyst there is a gradual increase in the size of the mitochondria and an increase in the number of cristae. We believe that the number and modifications of cristae indicate stages of mitochondriogenesis and the level of enzymatic activity in which this organelle is engaged during oogenesis and early embryogenesis.

Notes: The reproductive tracts of several species of lizards were examined to understand the events assoclated with the transport of discharged oocytes following ovulation. At the onset of the reproductive cycle the regressed ovaries and oviducts appear as inconspicuous structures pressed against the dorsal body wall. As the reproductive cycle progresses, they undergo marked changes in position and size. The oviducts migrate ventrally and surround the growing ovarian oocytes, which move anteriorly where coelomic space is more abundant and eventually press intimately against the infundibulum. When ovulation occurs the ostium is in a remarkably strategic location for directly receiving the ovulated oocytes. The virtual isolation of the ovaries from the general coelom by the encapsulating oviducts, and the intimate association of the pre-ovulatory oocytes with the infundibular ostium do not support the current concept advocating the migration of loose ova following ovulation. An alternative explanation for the “trans-coelomic migratiion of ova” is proposed.

Notes: A histological study of the spleen of the Brown-headed cowbird, Molothrus ater, is presented.One of the most striking differences from the mammalian spleen is the lack of trabeculae and of smooth muscle in the capsule which would suggest that the spleen is not an organ of storage or pumping of blood. Without trabeculae to foster the close association of the major arteries and veins, these vessels take separate courses. Their support is provided by elaboration of the collagenous and reticular fibres of the stroma.A peculiar ovoid structure, the ampulla, carries the blood from the terminal arterioles of the white pulp to both the sinusoids and the reticular cords of the red pulp so that both open and closed circulations are seen but the open circulation predominates. The ampulla has perforated walls consisting of a simple cuboidal endothelium surrounded by a dense reticular sleeve. Leucocytes were seen passing through the holes in the walls of the ampullae by diapedesis. It is suggested that the ampullae may be contractile and act as sphincters controlling the flow of blood through the spleen.The major functions of the spleen appear to be haemopoiesis, production of antibodies, and filtration of blood.

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 cyclic changes in the testis of the five-spined stickleback Eucalia inconstans (Kirtland) were studied histologically. Specimens were trapped between July 1965 and July 1967 in a shallow pond near London, Ontario.A three-dimensional microscopic study showed a main vas deferens and a system of primary, secondary and tertiary tubules.The testis cycle was divided into seven arbitrary stages. Spawning takes place from mid-April to mid-July. This is followed by the division of primary spermatogonia which are located along the walls of the tubules, producing cysts of spermatogonia enclosed in connective tissue which is surrounded by a thin epithelium. Both primary and secondary spermatocytes develop within these cysts. Breakdown of the cysts occurs with the development of spermatids and spermiogenesis occurs while spermatids are free in the tubules. Over-wintering of mature sperm takes place. Development of mature sperm from primary spermatogonia takes about 156 days.Germinal epithelium is absent but primary germ cells are believed to be those cells occupying the spaces between the tubules of the testis. No tissue which might be implicated in hormone production was observed.Phagocytic invasion of the testis has been studied. Massive infiltration by phagocytes is believed to be responsible for the sudden increase in testis weight observed during spawning. These cells ingest sperm nuclei and groups of them have been observed in the lumen of the tubules and the vas deferens, probably on their way out of the body.

Notes: Virgin mosquitoes were studied with the electron microscope. Spermathecal duct walls contain cuticle, epithelium, and a richly innervated spiral muscle; myocytes are linked by desmosome-like attachment plaques to the underlying epithelium. Periductal cells along upper portions of the ducts have a large secretory droplet within a highly irregular extracellular lacuna and are attached to a long secretory ductule through which finely granular material is delivered to the duct lumen and this enters the spermathecae. Basal gland cells of spermathecae have short ductules containing secretion in virgins. Secretory material in spermathecae of virgins does not form a complete internal membrane.

Notes: The ontogenetic sequence of cranial bony structure from initial ossifications through metamorphosis in Ambystoma texanum is described on the basis of 128 cleared and stained specimens. For convenience of discussion nine stages are recognized on the basis of conspicuous events. Cranial bones ossify and are modified in a definite sequence, and comparisons of complete sequences among groups of salamanders may prove useful in classification and in better understanding of relationships.

Notes: The distribution of glycogen, lipids and succinic dehydrogenase (SDH) in twitch and tonus fibers of several amphibians and birds is described, and the correlation of histochemical properties with fiber structure and function is discussed. Twitch and tonus fibers were identified histologically by the presence of Fibrillenstruktur and Felderstruktur respectively. The rectus abdominis, sartorius and semitendinosus were studied in Rana pipiens, Xenopus laevis and Necturus maculosus; the pectoralis major, pectoralis minor, anterior latissimus dorsi and posterior latissimus dorsi were investigated in Gallus gallus and Passer domesticus. Periodic acid-Schiff was used to stain for glycogen, Sudan Black B for lipids and Nitro BT for localization of SDH activity.In amphibian muscles, fibers with Fibrillenstruktur and Felderstruktur constitute the rectus abdominis. Except in one case, only Fibrillenstruktur fibers were seen in the sartorius and semitendinosus. In the avian muscles, fibers with Fibrillenstruktur comprise the pectoralis major, pectoralis minor and posterior latissimus dorsi, while fibers with Felderstruktur constitute the anterior latissimus dorsi. These types of muscle fibers showed no consistent pattern in the distribution of glycogen, lipids and SDH. The evidence precludes the use of such data alone for distinguishing twitch (Fibrillenstruktur) and tonus (Felderstruktur) fibers.

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: The fine structure of the developing gizzard of the chick embryo has been studied to define the sequence of events in cytodifferentiation of the epithelium and to look for morphological evidence of epithelio-mesenchymal interaction. During the fourth day of incubation epithelial cells begin to form mucous secretory granules, later massive glycogen deposits appear, and finally by day 8 numerous cell processes have formed. Tissue was prepared by a number of methods to stain material associated with cell surfaces. At the time induction is presumbably occurring such stainable material is abundant. Epithelial and mesenchymal tissue components when cultured transfilter show no inductive effects and stainable cell surface material is greatly reduced near the epithelium.

Notes: An approximate 1:1 ratio of myelinated to unmyelinated fibers was established in counts from electron micrograph montages in nerves of the newt, Triturus (Notophthalmus) viridescens. The number of myelinated fibers correspond to the number counted with the light microscope after osmium fixation. Light microscope counts of silver impregnated sections yielded a value slightly higher suggesting that, except for bundles of unmyelinated fibers, the silver technique revealed mainly myelinated fibers. The results were used to reassess previous quantitative studies on the relation between number of nerve fibers and the control which nerves exert on regeneration. For a truer estimate of the number of axons affecting regeneration, fiber values previously reported should now be doubled to include the large number of unmyelinated fibers. However, calculations show that the unmyelinated fibers contribute less than 3% of the total neuroplasm in the peripheral nerve.Finally, counts made of Schwann cells and fibroblasts show that the latter are few in number.

Notes: A histological study was undertaken of the differentiation of the lymphomyeloid complex of larvae of the common leopard frog, Rana pipiens, reared at 18-21 °C. Immature lymphocytes are first recognised in the thymus and pronephros at stage I of Taylor and Kollros ('46). By the end of stage II, small lymphocytes are regularly found among the predominant larger lymphoid cells in the thymus, in which corticomedullary differentiation has begun. At this time, a few small lymphocytes are also apparent in the ventral cavity bodies, lymph gland, pronephros, mesonephros and intestine, but rarely occur in the spleen. During stages III and IV extensive development of these components of the lymphomyeloid complex occurs. The organs now contain large numbers of mature lymphocytes and have attained states of differentiation that remain essentially similar in subsequent larval stages. By stage V, small epithelium-associated lymphoid accumulations are abundant throughout the length of the gastrointestinal tract. The anlagen of the procoracoid body and bone marrow appear just prior to metamorphosis.The kidneys are the main sites of blood formation in the larva. Masses of granulocytes are also usually found in the abundant ventral cavity bodies. A consideration of the roles of each of the organs provides insight into the ontogeny of the immune system of the Anura in general.

Notes: The sexual apparatus was studied in 100 adult axolotls (Siredon mexicanum) for 13 different spawnings. The ages of the animals varied between two and six years. Additional material from Indiana University was also studied. Altogether there were 55 female and 52 male adult axolotls represented. The purpose of the study was to investigate the limits of the variations occurring in normal axolotls and to compare the incidences of variations and developmental abnormalities in adult animals of both sexes at various ages and belonging to different strains.Among the 13 spawnings examined, five strains were completely normal in 100% of the animals, but the remaining eight strains all included abnormal animals. The incidence of abnormal animals in some of these latter strains was 40% or even 50%. Since all of the animals were under the same conditions, the variability and the occurrence of developmental abnormalities most likely depended upon hereditary factors. Among 55 females, only seven (12.7%) were abnormal; only four of these had developmental abnormalities, and only one was hermaphrodite. Among 45 males from the author's axolotl colony, 16 (28%) were abnormal. Of these latter, six had no sex cells or very few; this variation must be regarded as a developmental abnormality. All of these malformations resulted from major degeneration processes and abnormal morphogenesis.Arrested development was also observed in many males. Spermatozoa were completely absent from the testes of eight animals. In the additional material from Indiana University (testes from 7 males), there was also one completely abnormal testis with major degeneration processes and complete absence of sex cells. It is evident that variability and the incidence of developmental abnormalities in the sexual apparatus in adult axolotls of some strains are very great.

Notes: The sensillum of the ear of Feltia subgothica contains two ciliated receptor cells, the A cells. The cilium of each is enclosed within a well developed scolops consisting of a cap, a set of scolopalial rods and a collar, an unusual structure contained within the dendrite. The tip of the cilium is inserted in a channel in the scolopalial cap.The cap is linked to the tympanic membrane by a series of three structures: a cap cell, a microtubular shaft and a microfibrillar plug. The two latter structures are heavily reinforced by cytoskeletal elements and the microfibrillar plug is actually continuous with the tympanic membrane. These three structures transmit the vibration of the tympanic membrane to the scolops.The simplicity and accessibility of the ear suggests that it might be a good system in which to investigate cellular events associated with transduction of sound in these receptors.

Notes: The segmental anatomy of Harmothoë imbricata deviates from the plan of a typical errant polychaete only slightly. The body is partitioned into 37 nonmetameric segments and is covered by 15 pairs of elytra. The segmental musculature consists of paired dorsal and ventral longitudinal muscles, pairs of dorso-ventral muscles, and in places the external surface of the worm is covered by a sheet of circularly coursing muscle fibers subjacent to the cuticle. The dorsal tubercles, elytrophores, cirratophores and ventral cirri are moved by muscles derived from segmental and intrinsic parapodial muscles. From the anatomy it is surmised that the lateral bending of the worm during swimming is due to cycles of activity involving the longitudinal muscles (S-waves). During a cycle of parapodial stepping, parapodial levators and promotors raise a parapodium from the substrate and direct it forward (the recovery stroke), at which time the muscles of the aciculum and setal sacs withdraw the neuropodial setae. During the power stroke parapodial depressors and remotors bring the tip of the parapodium against the substrate, applying a forward thrust and the neuropodial setae are extended. At the conclusion of the power stroke, the recovery stroke begins anew.

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: The present ultrastructural study of the hepatopancreas of Oniscus ascellus would seem to indicate that the entire gland functions as a true midgut and is involved in absorption and secretion. Two differentiated cell types, the S and B, are present throughout the gland except for a small area of the posterior or regenerative zone.Ultrastructural features that have been associated with absorption include the presence of a surface enteric coat, regularity of microvillar core filaments, an organelle free region under the microvilli and the uniform distribution of mitochondria below this area. These features are present in both the S and B cell types. Features that are typical of secretory cells include the presence of extensive arrays of parallel rough endoplasmic reticulum, the very active dictyosomes with dilated cisternae and large secretory bodies. These features are present in the B cell. Although occasional arrays of parallel endoplasmic reticulum were noted in the S cell, active dictyosomes with dilated cisternae were not evident.From this ultrastructural study it would appear that the B cell functions in absorption and secretion, while the S cell functions primarily in absorption. A cytochemical study is now in progress.

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 stolon of the colonial marine hydroid Podocoryne carnea differentiates sequentially as a function of age, forming four distinguishable regions characterized by epidermal cell differentiation: The Tip, New Stolon, Cnidogenic Masses, Old Stolon. Radioautographs of sections of colonies exposed to tritiated thymidine show that although cells of the epidermis and gastrodermis of the stolon incorporate the nucleoside into acid stable polynucleotide, cells of the stolon tips do not. Stolon extension is not, therefore, the result of a localized meristem-like growth zone.Stolon branching and new polyp formation are, similarly, not signaled by increased thymidine incorporation. The initial event heralding these morphogenetic activities appears to be the reorientation of epidermal cells along a new axis, and the acquisition of perisarc dissolving ability. This evidence is contraindicative of direct dependence of colony form on colony growth.The larger part of stolon epidermal cells are organized into cnidogenic masses where cnidocytes and possibly other amoebocytic cells are produced.Although no mitotic figures have been observed in gastroderm cells of the stolon, thymidine incorporation in this tissue occurs with the same frequency as it does in epidermis. Considerable numbers of gastroderm cells can be found in the gastric cavity. Frequently these and gastroderm cells in the stolon and polyps contain more than one nucleus.

Notes: The fine structure of the epidermis and cuticle has been described for the oligochaete Aeolosoma bengalense. The epidermis is a pseudostratified epithelium and consists of the following cell types: ciliated and nonciliated supportive cells, pigment cells and associated satellite cells, mucous cells, basal cells, and ciliated non-supportive columnar cells. Overlying and restricted to the supportive cells is a delicate cuticle composed of: (a) a discontinuous layer of membrane-bounded surface particles; (b) a thin filamentous layer of moderate electron density just under the surface particles; (c) a thicker inner filamentous layer of low electron density. Digestion with pronase effectively removes the cuticle. This, together with the fact that it stains with alcian blue and ruthenium red, indicates that the cuticle contains an acid mucopolysaccharide. Regeneration of the cuticle, following pronase treatment, is marked by the elaboration of numerous microvilli by the supportive cells. Most of the microvilli are transitory and evidence supports a microvillar origin for the cuticular surface particles. The presence of cuticular surface particles may be a characteristic shared in common by all oligochaetes and, perhaps, some polychaetes.

Notes: A histochemical study of the mucus-secreting cells in the epithelial lining of the alimentary tract of the ampullariid snail Marisa cornuarietis permits description of six types of glandular cells secreting carbohydrate-rich substances. These mucous cells are designated on morphological grounds as fusiform, club-shaped, ovate, goblet, saccular and elongated conical and their histology together with their distribution and relative frequency in the different organs is described.Histochemical analysis using various fixatives and numerous recently-developed histochemical techniques shows that four main types of mucosubstances are produced by the six cell types. (1) The fusiform and club-shaped cells secrete neutral mucosubstances with moderate-to-weak PAS reactivity and variable amounts of basic protein. (2) The ovate cells secrete a strongly PAS-reactive, neutral mucosubstance lacking associated basic protein. (3) The goblet and saccular cells elaborate predominantly PAS-unreactive, strongly acidic, and highly sulfated mucosubstances or sulfomucins. (4) The elongated-conical cells secrete a highly PAS-reactive, weakly acidic sulfomucin whose vic-hydroxyls are presumably located in close proximity to sulfate esters.

Notes: The fine structure of the antenna and of the antennal sensory cone, the largest of the eight antennal sensilla, of fourth instar larvae of the mosquito Aedes aegypti are described and discussed. The antennal integument supports and encloses only sensillar elements. The antennal sensory cone seems to be a chemoreceptor of a modified composite basiconic type. It is innervated by about 12 neurons grouped into six units. Each neuronal unit has a trichogen and tormogen cell, but no neurilemma or other accessory cells, associated with it. Stimulating molecules may diffuse directly through the non-perforate conical cuticular covering to the dendritic branches, and through six vacuoles between the dendrites and the epicuticle at the base of the cone. Peripheral vesicles in the cone, their probable formation from secretions produced in the junction body region, and their possible function in the stimulating mechanism of the sense organ are described and discussed. Dendritic neurotubules originate from ciliary tubules in the junction body region, in the dendritic plasma, or by branching. Tight junctions provide possible electrotonic coupling between all the dendritic branches of the sensillum, and between dendrites in each unit. The neuronal perikaryons and portions of the axons and proximal dendrites are not ensheathed, but extend naked in close proximity through the antennal hemo-sinus into an ensheathed nerve at the base of the antenna.

Notes: Two trionychid turtles, Trionyx ferox and Lissemys punctata, have similar and distinctive nasal cavities. Most of the parts of the nasal cavities are similar to those in other turtles, but the intermediate regions have many more small ridges and shallow sulci than do those of other turtles; these form a highly complex and distinctive pattern that varies in minor details. In turtles generally, a relatively large intermediate region appears to be correlated with strongly aquatic habits, which supports the interpretation that the vomeronasal epithelium of that region functions in olfaction in an aquatic environment.

Notes: The salivary gland of Periplaneta americana (L.) is innervated from both the stomatogastric nervous system (SNS) and subesophageal ganglion (SEG). Methylene-blue preparations, histological sections and electron microscopy revealed a pair of nerves from the SEG, each of which contains two axons 5-7 μ in diameter, and these are accompanied by several smaller ones. The nerves going to the salivary glands from the SNS contain a dozen or more axons, each less than 2 μ thick. Axons from two sources innervate the efferent salivary ducts, the acini, the anterior ends of the salivary reservoirs, and the reservoir suspensory muscles. A nerve which has reached an acinus forms a plexus upon its surface. Electron micrographs disclose penetration of axons with or without glial wrappings, into the intercellular spaces between gland cells. Axons without glial wrappings have been observed in intimate contact with gland-cell membranes, and several areas which resemble synaptic junctions have been seen.

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: Anterior pituitary glands of male rats (2, 3, 5, 8, 12, 25, 36, 52, 56, and 62 days of age) were processed for electron microscopy. During early postnatal stages secretory cells are found in various stages of differentiation and comparatively few secretory granules are seen. Nuclei are mostly irregular, and the nucleo-cytoplasmic ratio is large. Many free ribosomes are present; the endoplasmic reticulum is generally sparse and the Golgi complex small or invisible. Cells are of variable shape, and numerous cytoplasmic processes project into large intercellular spaces. Many electron-dense cells which often contain myelinlike figures are seen. Lysosomes and lysosomal precursors are frequently found in secretory cells, predominantly in somatotrophs, of all immature glands. Mitotic figures are numerous in early stages after brith and decrease in number as the gland grows in size. A gradual increase in cytoplasmic volume with concomitant differentiation of cytoplasmic components as well as accumulation of secretory granules, accompanied by loss of myelin-like figures and decrease in the number of electron-dense cells, is observed as the animal reaches the prepuberal stage. Few lysosomes are seen in cells of mature glands. At 36 days of age all secretory cells seem to have differentiated, and morphological features as well as granule content show little change until puberty is reached. Gonadotrophs attain their characteristic morphology later than other cells. Cilia are observed in all developmental stages but are relatively infrequent in the mature gland. The described ultrastructural characteristics reflect the degree of maturation as well as the functional capacities of secretory cells at particular stages of development.

Notes: Embryos of the viviparous teleost, “Characodon” eiseni, have unusual anal processes that function only during gestation and are lost shortly after birth. This study was undertaken to determine if the fine structure of the process epithelium supports the assumption that these cells have an absorptive function. The process epithelium is a single layer of columnar cells. At peak activity intercellular spaces become very large and isolate individual cells which simultaneously lose much of their cell mass. The cells are characterized by microvilli on their free surface, much pinocytic activity and by the formation of at least four different kinds of vesicles. There is much evidence that these vesicles fuse together. A distinctive characteristic of these cells is a system of tubules and flattened cisternae that somewhat resemble the endoplasmic reticulum yet they differ from it in several respects. It is suggested these profiles aid in fragmenting the cell at periods of peak absorptive activity, thereby increasing the cell surface. Possible mechanisms of food absorption are considered. The fine structure of these cells supports the contention that these embryonic processes serve as absorptive organs during gestation.

Notes: Under the electron microscope, the spermatozoon of Branchiostoma lanceolatum shows a spherical nucleus deeply grooved along its caudal third, a bistratified acrosome enriched by plentiful subacrosomal material, two centrioles, mitochondria fused into a single mass surrounding the centriolar region which is highly asymmetrical, a 9 + 2 flagellum tilted with respect to the longitudinal symmetry axis of the nucleus. The sperm of Branchiostoma shares the overall features of that of the Tunicata and fits in perfectly with the phylogenetic position of the Leptocardia.

Notes: One hundred fetuses of the Sprague-Dawley rat were used: ten for each prenatal day, beginning with the twelfth day of gestation. Pregnant animals were sacrificed, fetuses removed and subsequently fixed in buffered formalin solution. Fetal heads were dehydrated, embedded in paraffin, and sectioned serially in the rostrocaudal direction at 10 to 15 μ. Serial sections from fetuses representing each day of gestation were stained with either H and E, Mallory's trichrome procedure, Gomori's reaction for alkaline phosphatase, or Steedman's alcian blue reaction. At the twelfth day, the primary nasal cavities were first observed. One day later, the nasobuccal membrane was established, and the vomeronasal organ invaginated into the nasal septum. Following the rupture of the membrane, at the fourteenth day, the nasal and buccal cavities remained in communication until the palatal shelves fused with the septum, at the seventeenth day. Prior to the thirteenth day, the septal skeleton is mesenchymal. The ossification in the vomer started at the sixteenth day and expanded progressively throughout prenatal life. First glandular primordia, one on each side of the septum, were observed during the sixteenth day, the number increased to five at term. The ducts ended in single blind sacs, before the eighteenth day, afterwards, the ducts presented an increasing number of collateral and terminal branches. There was no evidence of mucigen secretion from the septal glands during prenatal life. The initial stratified olfactory epithelium differentiated morphologically into a vestibular, respiratory, and an olfactory epithelium prior to the sixteenth prenatal day.

Notes: The rejection of skin homografts in the snake, Thamnophis sirtalis is preceded by an infiltration of mononuclear cells into the graft bed. The initial arrangement of infiltrating cells in perivascular halos suggests that these cells emigrate from the blood stream of the host. A cytological study showed that the vast majority of the cells can be classified as small and mediumsized lymphocytes, monocytes and macrophages. Early stages of infiltration were associated with large proportions of lymphocytes while later stages were characterized by a predominance of macrophages. It was concluded that the mononuclear cells associated with graft rejection include large proportions of lymphocytes and macrophages and not just one kind of lymphoid cell.

Notes: The hamster nasal cavity consists of vestibular, non-olfactory and olfactory portions. Much of the non-olfactory nasal cavity surface is lined by cuboidal, stratified cuboidal, and low columnar epithelia, devoid of cilia. Goblet cells and ciliated respiratory epithelium are present over only a small portion of the nasal cavity surface.The largest glandular masses in the hamster nose are the maxillary recess glands, the vomeronasal glands and the lateral nasal gland 1; these three glands contain neutral mucopolysaccharides (PAS-positive). Other nasal glands contain both acidic and neutral mucopolysaccharides; the staining reaction for acidic mucopolysaccharide is stronger in goblet cells and olfactory glands than in the other nasal glands.The ducts which open into the nasal vestibule are the excretory ducts of compound tubuloacinar serous glands. The one major PAS-positive gland whose duct opens into the nasal vestibule is the lateral nasal gland 1. The ducts of the compound tubuloacinar vomeronasal glands open into the lumen of the vomeronasal organ, which is connected to the ventral nasal meatus by means of the vomeronasal duct. The ducts of the branched tubuloacinar maxillary recess glands open into the maxillary recess. Few ducts open into the caudal half of the nasal cavity.

Notes: A differentiated segment, analogous in location and structure to the first portion of the sexual segment of the males, but much smaller, is observed in the renal collecting ducts of female C. lemniscatus. In addition to this first portion, with cells full of granules strongly positive to periodic acidleucofuchsin, males have a consecutive second portion, with granules localized only in the apical part of the cells, moderately positive to the reaction mentioned and with a marked affinity for orange G. The two portions of the male sexual segment are considered to correspond to the middle and final parts of the collecting ducts; the initial part in both sexes and the final one in the female are mucigenous.

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: The fine structure of the ovary in the serpulid Spirorbis borealis has been described. The ovarian wall consists of from one to several layers of peritoneal cells. Peritoneal cell processes extend deep into the ovary and may be seen between developing oocytes. Although young oocytes may also be in close apposition to one another, intercellular bridges have not been observed. When primary oocytes at the surface of the ovary reach a diameter of about 20 μ, they start to erupt into the coelom. Ovulation results from a simple separation of overlying peritoneal cells which lack specialized cell-to-cell contacts. Once a free surface of an ovulating oocyte is exposed to the coelom, microvilli and primary coat develop. Previtellogenic coelomic oocytes are often observed in close proximity to putative neoblasts (perivasal cells), which suggests a possible functional relationship. The confusion that extists between germ cells, peritoneal cells, and so-called neoblasts in polychaetes is discussed.

Notes: The ultrastructure of the centriolar satellite complex in the spermatozoon of the hydroid, Pennaria, is presented. The complex consists of nine spoke-like arms which emanate from the distal centriole and of nine wedgeshaped connectives which extend into the flagellum joining each of the alpha doublets and the flagellar plasmalemma. Based upon these observations a new model for the structure of the centriolar satellite complex is proposed. In addition, similar centriolar satellite complexes are reported in the spermatozoa of two echinoderms, Ctenodiscus crispatus and Thyone briareus, in support of the proposed model.

Notes: Males of the European elm scale, Gossyparia spuria (Erioccoccidae) have two Malphigian tubules, each made up of mononucleate and binucleate cells. Both types of cells may contain heterochromatic (H) chromosomes which form an H body. The cells with H bodies (H cells) usually appeared singly anywhere along the tubule. However, when two or more H cells were present they tended to be closer to each other than would be expected by chance. The possible origin of this tendency is discussed. Following squashing, the nuclei of the binucleate cells were much larger than those of most other somatic cells, suggesting that they were highly endopolyploid. However, the H bodies of the cells of the tubules were of about the same size as those of the other cells. These observations suggested that the H chromosomes of the binucleate cells did not replicate while the euchromatic chromosomes of these cells replicated several times. The great majority of the nuclei of the H cells contained a single H body per nucleus. An analysis of the number of H bodies in binucleate cells indicated that when two H bodies were present in the same nucleus they usually did not fuse. Thus, they were believed also not to fuse in the mononucleate cells. Since almost all the mononucleate H cells had only a single H body (rather than 2) it was concluded that they did not originate from binucleate cells by nuclear fusion.

Notes: The morphology of the rectal pads of two cockroaches, Blattella germanica and Blaberus giganteus is described and contrasted with that of Periplaneta americana, studied previously. The columnar absorptive cells of the three species are similar in structure. However, Blattella and Blaberus rectal pads have a second type of cell, termed the secondary cell, that is not present in Periplaneta. The secondary cells are embedded in the pad epithelium and have crypts of cavities opening into the subepithelial sinus. In addition, a multilayered sheath is present between the pad cells and the sinus. The sheath acts as a barrier, perhaps of low permeability, between the subepithelial sinus and the pads. It is interrupted only at the borders of the secondary cells. A mechanism for fluid absorption is presented and the possible role of secondary cells is discussed. It is proposed that the secondary cells reabsorb solute from the sinus and that this solute can then be recycled through the pad cells. Structures resembling neurosecretory terminals within the cavities of the secondary cells may be involved in regulation of recycling. The arrangement of the rectal pads in these insects has structural and perhaps functional similarities with other transporting systems, particularly the cryptonephric system.

Notes: Pyroantimonate precipitate indicates that the epithelium of the proximal tubule is the only segment of the tubular nephron of the fresh water lamprey where large accumlations of cations are distributed. Unusually large amounts of reaction product are located within the lateral intercellular spaces and within vesicles closely associated with the plasma membrane at the lateral and basal surfaces. This technique suggests the continuity of these vesicles with the plasma membrane and alludes to the possibility of an endomembranous system of vesicles and the intercellular spaces as vehicles for ion transport. Lateral intercellular spaces of proximal tubules of lower vertebrates may play a different role in kidney function that their counterparts in higher vertebrates.Osmium-zinc iodide has a specificity for certain cells within the proximal, intermediate, and distal segments, but no structural differences are noted when these cells are compared to unstained cells. Smooth endoplasmic reticulum remains unstained in the distal segment but the stain has a strong affinity for elements of the Golgi apparatus, lysosomes, and the nuclear envelope of all cell types. This technique does not suggest a structural or functional similarity between cells of the distal segment and the chloride cells of the gills of teleosts.

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: It is possible to monitor the electrical activity of the motor neurons of Drosophila by recording the electrical activity of the muscle fibers. We have found that it is possible to specify the location of the subcuticular terminations and to describe the orientation within the thorax for the individual muscle fibers, because of the large size of the fibers and because the surface anatomy of Drosophila is known in detail. A map has been made to indicate the location of the muscle fibers with respect to superficial landmarks. The importance of the stereotaxic map for physiological studies is discussed.

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: 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: 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 parathyroid glands of fresh-water turtles (Pseudemys scripta and Chrysemys picta) are composed of cords of cells in which dark and light variants of chief cells and occasional oxyphil cells can be distinguished. Cytoplasmic granules measuring about 0.3-0.4 μm and all the cellular organelles associated with protein and carbohydrate synthesis can be seen in both dark and light chief cells; the cytoplasm of oxyphils is packed with mitochondria which obscure other organelles. An unusual feature of the dark chief cells is the presence of crystalline-like material within parallel arrays of cisternae of rough endoplasmic reticulum. A similar crystalline-like structure is seen occasionally within some cytoplasmic granules.

Notes: Middle and inner ear anatomy correlates with neurophysiological responses to a wide range of sound frequencies for species of the Gerbillinae representing generalized, intermediate, and specialized anatomical conditions. Neurophysiological data were recorded from 81 specimens of 13 species representing six genera. Anatomical parameters involved in the process of hearing were correlated with the neurophysiological data to assess the effects of different degrees of anatomical specialization on hearing. The 13 species tested in this manner have graphic curves of auditory sensitivity of remarkably similar disposition over the frequencies tested and to those published for Kangaroo Rats. Ears with anatomical specializations show greater auditory sensitivity.The natural history of the Gerbillinae, particularly the kinds of predators, degree of predation, and habitat is reviewed and utilized to interpret the significance of the degree of auditory specialization in the forms studied and to evaluate the prevailing hypothesis that these specializations enhance the ability of these rodents to survive in open desert situations by detecting and evading predators.The middle ear anatomy of five additional genera and species was also studied. Thus, data on the entire spectrum of gerbilline middle ear morphology provide an evolutionary sequence. Certain anatomical parameters of the organ of Corti show a degree of specialization parallel to that of features of the middle ear. The morphological changes and possible functional roles of these features are considered.A very high correlation exists for degree of specialization and aridity of habitat, thus specialization increases with increasing aridity. This increased specialization may result from more effective predation in open xeric environments. Auditory acuity for a wide range of low frequency sounds augmented by auditory specialization is hence more advantageous here. There does not appear to be selection for hearing at particular frequencies in this range. The peaks of greatest auditory sensitivity appear to correspond to the resonant frequencies of the different components of the middle ear transformer and cavity.

Notes: The day-by-day development of the alimentary system of the sheep embryo from 14 to 34 days is documented and described. This includes development of the mouth, the pharynx and its derivatives, esophagus, stomach, intestine, cecum, pancreas and liver.This work provides standards within the normal range of development of the ovine alimentary system on which studies of abnormal development can be based.

Notes: The developmental anatomy of the sheep in the early prenatal period (14 to 34 days) was studied using embryos of known coital age, and embryos of known size with estimated coital age. Characteristics of the embryos were studied by gross observation under the dissecting microscope, and by means of serial sections. The period of the ovum (from conception to 10 days) and the early embryonic period (from 11 to 14 days) are summarized from the literature.This work provides a detailed, systematic account of embryonic development in the sheep and establishes size-age standards. Anatomical features encountered in the normal development of the sheep embryo are documented day-by-day because they are essential for studies of teratogenesis and early prenatal mortality.

Notes: The morphology of the following eight major ossicle types is described and illustrated for the goniopectinid asteroid Ctenodiscus crispatus: terminal plates, superomarginal and inferomarginal ossicles, adambulacral and ambulacral ossicles, odontophores, oral intermediate plates, and superambulacral ossicles. Development, variation, and relationships with soft body-parts and with other ossicles are embphasized. Each ossicle type is distinguished by numerous structures related to its function and to articulation with adjoining skeletal elements. Because major structures (such as pustules, alveoli, and articulation surfaces) distinguishing ossicle types develop early during ontogeny, immature ossicles are readily identifiable. However, changes in form and orientation of these structures occur during ossicle growth. Ontogenetic changes are influenced by development of associated skeletal and soft parts. Ambulacral and adambulacral ossicles near the peristome are highly modified but retain the basic characteristics of structure and orientation which define these major types of skeletal elements.

Notes: Post-fertilization events leading to the cleavage of the zygote of the sea-urchin, Arbacia punctulata were examined with the light and electron microscopes. Prior to prophase of the first cleavage division, endoplasmic reticulum and annulate lamellae become organized around the zygotic nucleus to produce a crescent-shaped structure which is defined as the streak (Harvey, '56). With the advent of prophase the streak undergoes morphogenic events which lead to the formation of the mitotic asters. During this transition there is a loss of annulate lamellae and a concomitant increase in endoplasmic reticulum. Annulate lamellae are not found as a part of the mitotic apparatus and are not again observed within the embryo until the two cell stage. During telophase, karyomeres are formed which consist of chromosomes delimited by a porous bilaminar envelope. Blastomere nuclei are produced following the fusion of the outer laminae, and subsequently by the fusion of the inner laminae of the envelopes encompassing the karyomeres.

Notes: The structure and polysaccharide constitution of the jelly capsule of the egg of Rana pipiens is described. Microscopic examination of the jelly capsule revealed the presence of five discrete jelly layers that differed clearly in their response to selected cytochemical tests. These layers were classified as M1-through M5 from the inner to the outermost layer. A sixth layer occasionally could be observed between M3 and M4.All layers contain neutral mucopolysaccharides. In addition layers M1 and M3 contain sulphated mucopolysaccharides, M2 and M4 contain non-sulphated acid mucopolysaccharides, and layer M5 contains both sulphated and non-sulphated acid mucopolysaccharides. M2 may also contain a small quantity of sulphated mucopolysaccharides. The layer that occasionally appears between M3 and M4 is probably an area in which free acidic groups are in higher concentration than in adjacent areas rather than being a discrete jelly layer. Neither hyaluronic acid nor sialic acid was localized by the methods employed.The possible significance of some of these constituents is discussed.

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: Myoepithelial cells were present between the basal lamina and the acinar secretory cells of human labial salivary glands. In form and disposition, they resembled myoepithelial cells in the major salivary glands. Many of these cells possessed single cilia on their upper surfaces. Such cilia occasionally extended into invaginations of the overlying secretory cell.The intercalated ducts were variable in occurrence. Their epithelium ranged from columnar to squamous, and showed few signs of secretory activity.Few intralobular ducts possessed basal striations. While mitochondria were abundant in non-striated cells, they were randomly disposed in both basal and apical cytoplasm, and the basal plasmalemma showed only occasional infoldings. The paucity of true striated ducts in labial salivary glands may be responsible for the high concentration of sodium and chloride in unstimulated labial gland salivary secretions.

Notes: Gravimetric and histologic modifications in the pigeon were studied following chronic therapy with ACTH and metopirone (SU 4885) for a period of 15 days. The organs studied were proventriculus, duodenum, heart, kidney, salivary gland, pancreas, liver, uropygial gland, thymus, spleen, bursa fabricii, testis, ovary, islets of Langerhans, adenohypophysis, thyroid and interrenal and chromaffin tissue of the adrenal gland. Induced states of hyper- and hypoadrenocorticalism elicited pathomorphic changes in endocrine and reproductive systems and some other organs of the pigeon. There were many differences and similarities in the nature of response of some organs following the two experimental conditions. Many of these cellular interactions might have resulted from alteration of interrenal function in the pigeon.

Notes: The pharynx, intestine and respiratory duct of Xenopus laevis were examined by light and electron microscopy, at different stages of the metamorphic cycle, through climax.It is well known that preclimactic larvae are suspension feeders and that after climax specimens feed on solid food. It is shown that the histology of the pharynx and the alimentary canal changes in adaptation to the change in the mode of feeding.Suspension feeding utilises ciliary activity but after climax cilia have disappeared from the pharynx and alimentary canal, when new neuromuscular mechanisms are utilised in feeding.Other morpho-histological changes in various intestinal and respiratory tissues are likewise considered in terms of functional activity.

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: A cephalic organ of presumed sensory function is described in nauplii and copepodids of the ascidicolous copepod Doropygus seclusus Illg. The receptor, located bilaterally in the anterodorsal head region, is composed of dendrites of extra optic protocerebral origin which have ciliary protrusions with basal bodies, no rootlets, and a basal infrastructure of the 9 + 0 type. The cilia do not branch and their distal terminations contain only one to four microtubules. In nauplii and free-living copepodids, a large epidermal supporting cell encapsulates the end of one dendrite and its cilia in a sac. Other dendrites and their cilia pass through the supporting cell and, terminally, the cilia escape to form a whorled fascicle which contacts the anterolateral cephalic cuticle. The latter end organ reaches its greatest development in the second copepodid stage  -  the stage which infects the ascidian. All of the symbiotic stages of the copepod have only a proportionately smaller end organ of the saccular type and apparently lack the end organ consisting of whorls of ciliary ends. The function of the receptor is unknown, but it is suggested that the end organ which disappears in the symbiotic stages functions in second copepodids in host recognition.

Notes: The epidermis of Eisenia is covered by a cuticle and rests on a basement lamella. The cuticle, which is resistant to a variety of enzymes, is composed of non-striated, bundles of probable collagen fibers that are orthogonally oriented and are embedded in a proteoglycan matrix. The basement lamella consists of striated collagen fibers with a 560 Å major periodicity. Proximity and morphology suggest that the epidermis may contribute to both the cuticle and the basement lamella  -  that is, the single tissue may synthesize at least two types of collagen. The epidermis is a pseudostratified epithelium containing three major cell types (columnar, basal and gland) and a rare fourth type with apical cilia. The esophagus is lined by a simple cuticulated epithelium composed predominantly of a single cell type, which resembles the epidermal columnar cell. Rare gland cells occur in the esophageal epithelium, but basal cells are lacking.

Notes: Gill development begins on the sixth day of incubation at 10°C and is complete by 31 days (hatching). Gill arches are formed by fusion and perforation of ectoderm and endoderm across the pharyngeal wall. A primary branchial artery forms within each arch and a second branchial artery forms as a branch from its ventral end. A series of filament loop vessels forms connecting the two arteries and when several are patent a unidirectional blood flow is established via afferent (second) branchial artery, filament loop vessels to efferent (primary) branchial artery. Part of the efferent branchial artery just above its junction with the afferent branchial artery constricts and occludes. It is suggested that this change in the pattern of blood flow is dependent on differences in resistance of the two branchial arteries. A later extension of the gill ventrally is thought not to be homologous with similar regions in elasmobranchs and Acipenser.

Notes: Scanning and transmission electron microscopy studies were conducted on the antennal sensory sensilla of the hymenopteran parasitoid, Cardiochiles nigriceps Viereck, of the family Braconidae. Distinct morphological differences were found between the chemoreceptors of the male and female. Curved, non-fluted, thin-walled sensilla were found to be very abundant on the male and restricted in location and number on the female. Trichoid, placoid and fluted basiconic sensilla were numerous on the antennal flagella of both sexes. Smooth basiconic sensilla were restricted in number to one per flagellar segment in both sexes. Behavioral data suggest that bent-tipped, thick-walled sensilla unique to the female are involved in detecting a chemical(s) emitted from the host, Heliothis virescens (Fab.).

Notes: The biomechanical role of the mammalian clavicle and the functional significance of the aclaviculate condition were investigated. Shoulder movements in rats (Rattus norvegicus) with excised clavicles were compared to those of normal rats by biplanar plate radiography. Shoulder movements during walking of the claviculate American opossum (Didelphis marsupialis), and aclaviculate raccoons (Procyon lotor) and cats (Felis domestica) were compared by biplanar cineradiography.The mammalian clavicle, where present in its complete form, exerts both a “spoke” and a “strut” effect on shoulder movement. By maintaining a fixed distance between the acromion and manubrium, the clavicle ensures that relative movement between these structures is arcuate. Aclaviculate mammals, in contrast, have linear shoulder excursions that are nearly parallel or slightly oblique to the median plane, depending on the conformation of the thorax. Medial collapse of the shoulder in aclaviculate rats demonstrates that the clavicle is under compression, and thus acts as a strut.Reduction or loss of the clavicle, which has occurred independently in numerous mammalian phylogenies, has been regarded as an adaptation for greater shoulder movement and hence increased stride. However, on present evidence clavicular reduction in cursorial mammals appears to be more directly related to a linear excursion of the shoulder joint and a restriction of limb movements to a sagittal plane.

Notes: The tail of Teratoscincus scincus has dorsal scales that have tubercles on their dorsal and ventral surfaces. Sounds are produced when these rub past each other as the excited animal moves its tail. The relative movement of scales is intensified by caudal torsion. The frequencies of the sounds cover a range from 9 to 25 kops and thus, differ from those produced during vocalizations.

Notes: The locomotor function of the caudal muscle cells of ascidian larvae is identical with that of lower vertebrate somatic striated (skeletal) muscle fibers, but other features, including the presence of transverse myomuscular junctions, an active Golgi apparatus, a single nucleus, and partial innervation, are characteristic of vertebrate myocardial cells.Seven stages in the development of the compound ascidian Distaplia occidentalis were selected for an ultrastructural study of caudal myogenesis. A timetable of development and differentiation was obtained from cultures of isolated embryos in vitro.The myoblasts of the neurulating embryo are yolky, undifferentiated cells. They are arranged in two bands between the epidermis and the notochord in the caudal rudiment and are actively engaged in mitosis.Myoblasts of the caudate embryo continue to divide and rearrange themselves into longitudinal rows so that each cell simultaneously adjoins the epidermis and the notochord. The formation of secretory granules by the Golgi apparatus coincides with the onset of proteid-yolk degradation and the accumulation of glycogen in the ground cytoplasm.Randomly oriented networks of thick and thin myofilaments appear in the peripheral sarcoplasm of the muscle cells of the comma embryo. Bridges interconnect the thick and thin myofilaments (actomyosin bridges) and the thick myofilaments (H-bridges), but no banding patterns are evident. The sarcoplasmic reticulum (SR), derived from evaginations of the nuclear envelope, forms intimate associations (peripheral couplings) with the sarcolemma.Precursory Z-lines are interposed between the networks of myofilaments in the vesiculate embryo, and the nascent myofibrils become predominantly oriented parallel to the long axis of the muscle cell.Muscle cells of the papillate embryo contain a single row of cortical myofibrils. Myofibrils, already spanning the length of the cell, grow only in diameter by the apposition of myofilaments. The formation of transverse myomuscular junctions begins at this stage, but the differentiating junctions are frequently oriented obliquely rather than orthogonally to the primary axes of the myofibrils.With the appearance of H-bands and M-lines, a single perforated sheet of sarcoplasmic reticulum is found centered on the Z-line and embracing the I-band. The sheet of SR establishes peripheral couplings with the sarcolemma.In the prehatching tadpole, a second collar of SR, centered on the M-line and extending laterally to the boundaries with the A-bands, is formed. A single perforated sheet surrounds the myofibril but is discontinuous at the side of the myofibril most distant from the sarcolemma. To produce the intricate architecture of the fully differentiated collar in the swimming tadpole (J. Morph., 138: 349, 1972). the free ends of the sheet must elevate from the surface of the myofibril, recurve, and extend peripherally toward the sarcolemma to establish peripheral couplings.Morphological changes in the nucleus, nucleolus, mitochondria, and Golgi bodies are described, as well as changes in the ground cytoplasmic content of yolk, glycogen, and ribosomes.The volume of the differentiating cells, calculated from the mean cellular dimensions, and analyses of cellular shape are presented, along with schematic diagrams of cells in each stage of caudal myogenesis. In an attempt to quantify the differences observed ultrastructurally, calculations of the cytoplasmic volume occupied by the mqjor classes of organelles are included.Comparison is made with published accounts on differentiating vertebrate somatic striated and cardiac muscles.

Notes: Anolis embryos have limb buds at the time eggs are laid and require about 39 days to complete development at 28°C. Rathke's pouch is present at five days, and the subdivisions of the adenohypophysis are differentiated by ten days after oviposition. The cells of the rostral half of the pars distalis (PD) are derived from the anterior face of Rathke's pouch; cells of the caudal half from the posterior face. Lateral lobe cells differentiate on the lateral margins of the developing caudal PD, and knob-like outgrowths of this tissue attach to the walls of the diencephalon to form the pars tuberalis (PT). Subsequently, the cells of the PT lose their connection with the PD and become a pair of flattened oblong plaques. They reach maximal size in midincubation, and are gradually invaded by nervous elements and incorporated into the walls of the hypothalamus. Electron micrographs demonstrate that the embryonic PT is secretory.Ultrastructurally the pars intermedia (PI) and PD are composed of parenchymous secretory cells in a framework of stellate cells. Stellate cells surround the lumen of Rathke's pouch and are connected laterally by complex junctions that exclude the secretory cells from the luminal surface. They extend in sheet-like processes among the secretory cells to the outer margin of the gland where they form a partial sheath within the basal lamina around the secretory tissue. As development proceeds, the lumen becomes subdivided and the resulting reduced lumina are recognizable as the forerunners of the follicles of the adult adenohypophysis.The cells of the PI are differentiated into secretory or stellate cells halfway through incubation. At this time only half of the cells of the PD can be so classified. Four of the five granulated cell types described in the adult are recognizable by mid-incubation; the fifth cell type (prolactin cell) becomes distinguishable within ten days thereafter, and at hatching appears to be actively synthesizing secretory products.

Notes: The hydranth of the gymnoblastic hydroid Syncoryne tenella is invested by a cuticle approximately 530 mμ thick which is continuous with the periderm of the hydrocaulus. The ectodermal cells of the hydranth possess regularly spaced microvilli orientated with their long axis perpendicular to the ectodermal surface. The microvilli project into the cuticle, and probably serve to anchor the cuticle to the ectoderm. In the hydrocaulus the periderm is loosely applied to the ectoderm: in this region microvilli are absent from ectodermal cells. The periderm is a layered structure composed of finely filamentous material. No structural basis is found for the previously reported differential staining of peridermal layers in the hydrocaulus.

Notes: The nuchal organs of polychaetes from four different families (Nereidae, Nephtyidae, Phyllodocidae and Glyceridae) were examined with the light and electron microscopes. In each case, the organ consists of ciliated cells and primary sensory elements. The ciliated cells are similar to the cells of the adjacent epidermis but bear motile cilia. Primary sensory neurons are situated within the organs in Nephtyidae and Phyllodocidae, but are located within the brain in Nereidae and Glyceridae. Each sensory cell gives rise to a distal process which penetrates between the ciliated cells to form an apical sensory bulb bearing modified cilia. Apically these processes are lined with juxtamembranous plaques. The ciliated cells are innervated by efferent axons from the brain, and in Nereis the axons appear to be peptidergic. The elements comprising the nuchal organs closely resemble those of the vertebrate olfactory mucosa.

Notes: The cuticle of five species of Oligochaeta, chosen to represent differences in size and a variety of biotopes, was studied electron microscopically after fixation with the acrolein-TAPO-osmium tetroxide method. Five distinct layers in the cuticle of all studied species were found. Staining with lead and uranyl ions or with silver proteinate visualized basically the same structural components of the cuticle, but the degree of electron opacity and the distribution of the electron-opaque stain in these components differed according to the staining method used. Since the acrolein-TAPO-osmium tetroxide method visualized the cuticular zones preferentially stained by Thiéry's silver proteinate method, it was concluded that the TAPO method may be considered suitable for the visualization of polysaccharides. Staining with phosphotungstic acid provided some information on the composition of the cuticle of Oligochaeta not obtained by staining ultrathin sections with lead and uranyl ions nor with silver proteinate. The conclusion is that phosphotungstic acid binds to polysaccharides which do not contain vicglycol groups nor active sites responsible for the positive reaction with lead and uranyl salts. Structural components in the cuticle of the oligochaetes studied were characteristic for each species. The taxonomic value of such components, however, must be confirmed by examination of a larger number of species of oligochaetes.

Notes: Laboratory-reared outgrowths of the freshwater sponge Corvomeyenia carolinensis Harrison were examined using histological and histochemical techniques, supplemented by phase contrast observations of cellular behavior. The tissue and cellular components of the spongillid outgrowth region were defined in terms of function and morphogenic state. Archeocytes differ considderably, in both histochemical and morphological characteristics, from other cell types of the adult sponge, being histochemically similar to stem cells reported from a variety of developmental series. Archeocytes exhibit cytological characteristics of unspecialized cells capable of high levels of synthetic activity while other cell types of C. carolinensis, for the most part, can be characterized as fully differentiated cells displaying more restricted synthetic capabilities but often accumulating neutral mucoproteins. The presence of aggregates of amebocytes, not identifiable as archeocytes and possibly engaged in gemmule formation, is discussed in terms of current concepts of gemmulation and cellular developmental capabilities in sponges.

Notes: The ultrastructure of the gut regions of the marine filter-feeder Phoronis vancouverensis was correlated with enzyme activity as revealed histochemically. The oesophagus, proventriculus, and stomach epithlia showed intense esterase and acid and alkaline phosphatase activity. The staining reaction was confined primarily to small globules in the apical cytoplasm of the epithlial cells. Electron micrographs of the same regions showed a high incidence of zymogenlike granules, with a corresponding abundance of ribosomes and of rough endoplasmic reticulum. Also, the proventricular and to a lesser extent the stomach epithelia were found to contain a large number of lipid bodies. This was confirmed with positive Sudan IV staining for fats.The intestinal region of the gut was found devoid of esterase and phosphatase activity. The epithelial surface in this region was found elaborated into microvilli. The entire gut is ci iated. A new paired-cilium apparatus is described in this phylum.From these findings Phoronis vancouverensis is concluded to be suitably adapted to its continuous filter-feeding existence, with the anterior gut epithelia synthesizing hydrolytic enzymes for release into the lumina of the proventriculus and stomach. Subsequently, in the hindgut the products of initial extra-cellular digestion are absorbed via the microvilli and treated intracellularly within the intestinal epithelium. The proventriculus is further thought to function in lipid absorption and storage. The presence of chromaffin-like granules observed in some proventricular and intestinal epithelial cells suggests that digestion in this phylum may in part be under neurosecretory control.

Notes: Ovarian changes during the reproductive cycle of the oviparous garden lizard (Calotes versicolor) are described. It ovulates from last week of June to first week of September but most often in July and August when the monsoon occurs. The number of eggs ovulated vary from 10 to 32. After ovulation, the ovaries are reduced in size. From October to May, the ovaries contain small pre-vitellogenic follicles, which increase in size in June when most of yolk deposition occurs. Several nuclei are seen in the ooplasm of pre-vitellogenic follicles; they are finally absorbed before yolk deposition starts. Follicular atresia generally occurs in follicles with polymorphic granulosae, in post-ovulatory ovaries. Presumably interstitial gland cells are formed by the hypertrophy of the theca interna cells of atretic follicles. Pre-ovulatory follicles have highly vascularized thecae and invaginations of the follicular epithelium. After ovulation, the follicle cells hypertrophy to form the luteal cell mass filling the follicular cavity. Fibroblasts, which appear to arise from the theca interna, invade the luteal cell mass and form septa. Capillaries occur in the luteal cell mass.