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Notes: Germ cells of the rat have been studied at the fine structural level from the time they are present in the epithelium of the embryonic gut until near the time of production of mature gametes in the adult. Particular attention has been paid to the form and location of dense, fibrous material (nuage) in the germ cells during that period of the life cycle. The nuage either exists as small discrete bodies in the cytoplasm or as “cementing material” situated in the interstices of mitochondrial clusters. It is present in primordial germ cells in the gut epithelium, in germ cells in indifferent gonads and in germ cells in sexually differentiated fetal, neonatal and adult rat gonads. It is sometimes associated with nuclear pores. Because it is present throughout much of the life cycle of the germ cells of male and female rats and it has been observed in various other mammals by previous workers, it is suggested here that it is a characteristic morphological feature of mammalian germ cells. In addition, there is considerable similarity in form and distribution of the nuage to the “polar granules” in insects and the “germinal plasm” in amphibians which are suggested to play a role in the determination of germ cells in these animals. The possibility that nuage may play a comparable role in mammals is considered.

Notes: The weight, density and percentage ash weight of the dry, fat-free osseous human skeleton have been examined from 16 weeks of gestation to 100 years of age. Data were drawn from 426 skeletons of American Whites and Negroes of both sexes.Weight increases exponentially in the fetus and continues to increase to early adulthood, most rapidly in the second decade. A decrease appears about the fourth decade and continues gradually. Estimated loss in skeletal weight throughout the adult period is, on the average, 15.6 gm per year. Proportionate contributions of divisions of the skeleton to its total weight change with age.Densities of bones follow the changing weight pattern. Volume and weight increase concomitantly to adulthood, when weight decreases but not volume.Percentage ash weight increases slightly in the total skeleton and in some bones during the fetal period, with no significant trend thereafter, indicating that change in weight of a dry, fat-free bone is accompanied by change in ash weight.Race and sex differences are not evident in the fetal skeleton, but become marked by the second decade of life: Negro skeletons exceed White skeletons and male skeletons exceed female skeletons in mean weight and density and, to a lesser degree, in percentage ash weight.

Notes: Evidence for a direct neural projection from the retina to the hypothalamus in the golden hamster (Mesocricetus auratus) is presented. In 25 blinded animals degeneration was followed in sections prepared according to the Wiitanen ('69) silver impregnation method. Degenerative axons were found in the optic tract, chiasm, and nerve, terminating in the lateral geniculate body and superior colliculus. A large collateral bundle of degenerating axons was observed curving medially and dorsally to enter the hypothalamus at the level of the mamillary body. This bundle turned diffusely rostrally and terminated on neurons in the ventromedial nucleus of the hypothalamus.It is proposed that two alternate pathways exist for the effect of photoperiodicity on the reproductive cycle in the hamster, one involving the pineal gland directly and the hypothalamus indirectly, and the other a direct retino-hypothalamic projection.

Notes: The objective was to study the fate of specific secretory cell types of the rat hypophysis when grown in primary monolayer cultures for periods ranging up to 32 days. The cells were identified immunohistochemically using peroxidase-labeled antibody. Early in the culture period TSH-cells were scarce and by 12 days they could no longer be identified. In most cultures LH-cells were well stained and common for eight to 12 days, after which they underwent involution. Growth hormone cells were a prominent feature up to six days but by 12 days they were declining in number, size, and stainability; in contrast, prolactin cells proliferated and were large and intensely stained throughout the period of study, ultimately becoming the dominant secretory cell type. Corticotropic cells also continued throughout the period of study without regression. Thus drastic shifts occur with time in the relative proportions of cell types in monolayer cultures of rat pituitary cells.

Notes: Distribution of mitotic nuclei in the biceps brachii of five day old mice has been studied after subcutaneous injection of 1 μCi/gm body weight 3H-thymidine. Serial transverse sections at 5 μm thickness were cut and the number of labeled nuclei per hundred fibers were determined on every fortieth section starting from the proximal end of the muscle.The proximal region of the muscle has significantly more labeled nuclei than either the belly region (P 〈 0.005) or the distal region (P 〈 0.001) of the muscle. The distal region of the muscle and the belly of the muscle did not differ significantly.Thus, most of the fiber elongation seems to take place at the proximal region of the muscle. As far as the transverse growth is concerned it appears that either every fiber at this stage is increasing in diameter or else the fibers which are undergoing an increase in diameter are randomly distributed throughout the body of the muscle, as no significant differences have been found in the percentage labeled nuclei in the four transverse areas of the muscle in the belly region.

Notes: The very fast extraocular muscles have both singly and multiply innervated fibers. The former are among the fastest vertebrate muscle fibers on record, whereas the latter are very slow. In this study single and multiple myoneural junctions were first identified in whole eye muscles of the mouse after staining for cholinesterase. Each group was then embedded separately for electron microscopy. Approximately 10% of the fibers were found to be multiply innervated. The multiple endings and the fibers they innervate resemble those of the tonic bundles of the frog. The majority single endplate is very large in surface view, has sparse junctional folds, and innervates a fiber very rich in mitochondria. These observations were contrary to some frequently held views regarding neuromuscular junctions of very fast fibers. A minority single endplate is smaller, has more junctional folds and innervates a large fiber with fewer and smaller mitochondria.

Notes: Longitudinal sections through the incisors of the rat show a continuous layer of ameloblasts on the labial surface of the tooth. This layer contains the entire sequence of developmental stages in enamel production. Using 1 μm Epon sections from the upper and lower incisors of 100 gm male rats, the ameloblast layer was divided into three main zones which were themselves subdivided into regions: (1) Presecretory zone which includes (a) region of ameloblasts facing pulp, itself comprising a posterior portion (upper 172 ± 35 μm; lower 187 ± 37 μm) and an anterior portion (upper 458 ± 28 μm; lower 503 ± 36 μm); (b) region of ameloblasts facing dentin (upper 1210 ± 81 μm; lower 1381 ± 90 μm). (2) Secretory zone, (a) region of inner enamel secretion (upper 2573 ± 141 μm; lower 4274 ± 160 μm); (b) region of outer enamel secretion (upper 1211 ± 60 μm; lower 868 ± 72 μm). (3) Maturation zone (upper 7335 μm; lower 10615 μm), (a) region of postsecretory transition; (b) region of maturation proper, consisting of portions of ameloblasts with striated border and portions of ameloblasts with unmodified apices; (c) region of pigmentation; (d) region of reduced ameloblasts.These regions are readily identified using clear cut morphological criteria. Length measurements made on a group of 40 rats established the reproducibility of this classification. Therefore, this classification will be used as a basis for future studies of cell population kinetics.

Notes: The human fetal thymus was studied at stages from 9 to 20 weeks of gestation. At 9 weeks of gestation the human fetal thymus contained lymphoid cells and was vascular although it was not yet lobulated nor did it have a cortex and medulla. By 12 weeks the thymus was lobulated and at 14 weeks a cortex and medulla could be distinguished, although the medulla was often more densely cellular than the cortex. By 18 weeks there were many lobules and a mature looking cortex and medulla. Large lymphocytes at all stages of thymus development studied were irregular in shape and often had blunt pseudopodia-like cytoplasmic extensions, or more slender cytoplasmic extensions. They also often possessed numerous elongated mitochondria, a large Golgi complex and strongly basophilic cytoplasm. Large lymphocytes were not attached to the epithelial cells by desmosomes although some of the cytoplasmic extensions from them were in association with extensions from epithelial cells. Primitive medium-sized lymphocytes at all stages studied were round in shape and had fewer mitochondria than the large lymphocytes. Epithelial cells were much less basophilic than the lymphoid cells and usually contained aggregates of glycogen. Occasional macrophages were observed within the developing thymus after 12 weeks of gestation and one granulocyte was observed within the thymus at 9 weeks while numerous granulocytes were seen within an interlobular septa at 14 weeks of gestation. Vessels were present within the thymus at all stages studied and at 9 weeks some had a boundary between the blood and thymus which consisted of only a thin endothelial cell and its basal lamina rather than the usual boundary of an endothelial cell and its basal lamina plus an epithelial cell and its basal lamina.

Notes: The ependymal tanycytes lining the ventral basal region of the third ventricle were studied in female rats during different stages of the estrous cycle. At mid-diestrus, the apical membranes of tanycytes were shown to be devoid of microvilli and of other surface irregularities. During proestrus, a multitude of microvilli and small bulbous protrusions characterize this region of the ventricular wall. These surface disruptions persist through estrus and disappear during diestrus. In addition, so-called supraependymal cells were observed and counted. Their numbers also vary with respect to the estrous cycle. The significance of these changes is discussed with respect to a possible mechanism for transporting substances from the cerebrospinal fluid (CSF) to the parenchyma of the hypothalamus and to the circulation.

Notes: Intact and denervated brown fat lobes of normal and cold-exposed mice were studied by light and electron microscopy. Following two weeks of denervation in normal and cold-exposed mice, denervated brown fat cells were hypertrophied because of lipid accumulation. In normal mice there was a transient increase in glycogen. In cold-exposed mice, the quantity of glycogen in intact and denervated brown fat was greater than in normal mice. Mitochondria increased in size, and the number of cristae was greater in intact fat of cold-exposed mice than in denervated brown fat. Carbon perfusion of blood vessels demonstrated a decreased capillary bed in denervated fat. Capillary constriction noted only in denervated brown fat is indicative of reduced blood flow.

Notes: Guinea pig visceral yolk sac endoderm cells are known to absorb proteins from the uterine lumen by the process of pinocytosis. Since previous studies have shown that the first step in protein absorption is the binding of the protein to an extracellular material on the surface of pinocytotic invaginations, it was thought that the surface coat might possess receptor sites for molecules which are subsequently absorbed. This study investigates the nature of the surface coat of the endoderm cells using ruthenium red, alcian blue/cetylpyridynium chloride-lanthanum and concanavalin A-peroxidase procedures. Results using these methods showed the presence of a surface coat on both the microvilli and pinocytotic invaginations. The coat on the pinocytotic invaginations was thicker than that on the microvilli. Concanavalin A receptor sites were separated from one another on the cell surface. Since only those pinocytotic invaginations which were open to the surface at the time of fixation would be “stained” by these methods, the procedures also show that the numerous tubules and vesicles in the apical cytoplasm do not all form an intercommunicating labyrinth open to the surface, even though most of them are part of a related functional system. The results indicate that the surface coat contains mucopolysaccharide components. In addition, concanavalin A receptor sites are present which are probably oligosaccharides associated with a glycoprotein component of the apical cell membrane.

Notes: The microscopic anatomy of the accessory glands of black-tailed prairie dogs (Cynomys ludovicianus) and thirteen-lined ground squirrels (Citellus tridecemlineatus) have been studied. In addition, the glands of a 5 cm fetal prairie dog have been described. Adult and fetal prairie dogs and adult ground squirrels have so-called seminal vesicles folded dorsally over the dorsal prostate with ducts leading directly to the urethra lateral to, but in the region of, the entrance of both the dorsal prostatic ducts and the deferent ducts. Histological studies of the seminal vesicles of both prairie dogs and ground squirrels showed that they were tubuloalveolar glands and were similar in structure to the dorsal prostates of each species. The fructose concentrations of the dorsal prostate and seminal vesicles of out-of-season prairie dogs were similar, and both glands accumulated fructose with the onset of the breeding season or with injection of testosterone propionate but the seminal vesicles accumulated more fructose than the prostate. On the basis of histological structure, anatomical relationships, accumulation of fructose and possible function as a coagulating gland it is proposed that the proper name for the so-called seminal vesicles in these species is craniodorsal prostate.

Notes: The phyllostomid bat, Macrotus waterhousii, undergoes delayed development. Implantation occurs early in the nine-month gestation, but the blastocyst remains relatively dormant until the sixth month when a chorioallantoic, hemodichorial placenta forms and a two and one-half to three-month growth pattern occurs leading to parturition.The barrier in the chorioallantoic placenta at first includes maternal capillary endothelium, but during the early part of the rapid growth phase the endothelium is replaced by blocks of syncytial trophoblast which penetrate the basal lamina. The basal lamina then apparently thickens and remains as the intrasyncytial lamina. Thus, the definitive barrier for maternal nutrients consists in order of passage of syncytial blocks, intrasyncytial lamina, syncytiotrophoblast, cytotrophoblast, fetal basal lamina and capillary endothelium.

Notes: Factors contributing to the retino-tectal course of the optic nerves in cyclopic and synophthalmic zebrafish embryos were evaluated. The eye abnormalities were produced by immersing blastula stage eggs in 3% ethanol for two hours. Approximately 50% of cyclopic eyes produced one optic nerve that exits from the eye to innervate one optic tectum. The remaining half of the cyclopic embryos formed optic nerves that were unable to exit from the eyes.In the synophthalmic embryos, two optic nerves were always produced. These nerves either joined within the partially fused retinas, or shortly after exit from the eyes, to form one nerve which entered the brain and innervated only one optic tectum. Crossing over was not seen within the fused eyes or after exit from the eyes.The resultant single optic nerves in the cyclopic and synophthalmic embryos innervated the side of the brain penetrated by the nerve. They entered in the floor of the forebrain, diencephalon, or midbrain, usually asymmetrically. Axial growth, directional orientation, and contact guidance of matrix configurations appeared an adequate explanation for the establishment of the retino-tectal pathway.

Notes: The parietal layer of Bowman's capsule in man and rat has been examined by transmission and scanning electron microscopy. In both species, cilia were found to be present in a regular pattern occurring one per cell. The cilia differed in length between the immature and mature human kidney, but were consistently located near the edge of the cell nucleus. Since they are not numerous enough to have a significant propulsive role, we have postulated that they may have some other specific function. In addition to the cilia, microvilli were regularly observed on the surface of the parietal cells. They tended to be more numerous along the margins of the epithelial cells and, in contrast to the cilia, their pattern was highly variable. This variability probably indicates that they are transitory structures which can be increased or decreased in response to as yet unknown stimuli.

Notes: Previously reported methods for the electron microscopic visualization of the surface layer (surfactant) of the alveolar lining cells have proved less than ideal and further development in this area is needed. Two percent agar in glutaraldehyde injected into the respiratory tree concurrently with vascular perfusion seems to offer some real advantage over techniques described by others. The combination of glutaraldehyde and agar acts both as an obstruction that holds surfactant against the alveolar surface and as a fixative due to the buffered glutaraldehyde component. This technique offers more consistent results and more extensive demonstration of the surfactant layer over the alveolar surface.

Notes: Glycol dehydration followed by rehydration prior to conventional fixation appears to demonstrate the essential identity of the thick filaments observed in unfixed, glycol dehydrated and conventionally fixed smooth muscle. Observed differences in the solubilities of actin and myosin filaments also suggest that the thick filaments of smooth muscle are not formed by the apposition of actin filaments or by the deposition of myosin upon actin filaments. Evidence that the thick filaments of smooth muscle are not formed by an unnatural aggregation of smaller myosin aggregates or by the dissociation of myosin “ribbons” during tissue preparation is also reported. Examinations of smooth muscle contracted or relaxed by pharmacological agents appear to indicate that the myosin content of smooth muscle is aggregated into filaments in both the contracted and relaxed cell.

Notes: The morphogenesis of cerebellum has been studied in 6-19 day old chick embryos after a single injection of 0.05 mg of cyclophosphamide into the yolk sacs on the fifth day of incubation. Besides degeneration of Purkinje cells, rate of development was markedly retarded as evidenced by late appearance of the fissures and folia of the cerebellum. Purkinje cells remained disorganised up to 18 days of incubation, though in controls they were arranged in a single line by the fifteenth day. The thickness of the external granular layer increased and persisted for a longer period in the treated embryos. The cytoarchitecture returned to normal on nineteenth day of incubation, but the size of the cerebellum was significantly smaller than that of controls (P 〈 0.001). Such transient disorganisation of the morphogenetic events in the neural tube may lead to inadequate and defective induction of surrounding mesenchyme, thereby resulting in defective skull formation through which the brain can herniate, i.e., exencephaly as reported in our earlier studies after cyclophosphamide administration in chicks (Singh et al., '71; Singh and Gupta, '72) and rats (Singh et al., '72).

Notes: Hamsters injected at 0900 on day 1 of the cycle (metestrus) with either 0, 5 or 15 IU pregnant mare's serum (PMS) were killed at 1500 of days 1 to 4 of the cycle and the ovaries prepared for light microscopy and for a quantitative evaluation of follicular development. In the untreated cyclic hamster, the maximal number of preantral follicles with eight or more layers of granulosa cells occurred between the afternoon of day 4 (proestrus) and day 1, coinciding with the highest blood levels of FSH and LH. It is concluded that the elevated preovulatory levels of gonadotropins not only induce the ovulation of the mature antral follicles but at the same time recruit the next set of follicles for development during the new cycle.By the afternoon of day 1, treatment with either 5 or 15 IU PMS recruited more follicles into large preantral and incipient antral stages than in the untreated hamsters. However, by day 2 the pattern of follicular distribution was similar between the 5 IU PMS and untreated group whereas considerably more antral follicles had differentiated in the animals given 15 IU PMS. The ability of 15 IU PMS to elicit superovulation therefore depends on the levels being initially high enough to mature more follicles at critical stages of their development; the prolonged biological half life of PMS then sustains these follicles throughout the cycle.

Notes: The sequence of cytological events from sperm penetration of the oocyte until emergence of the blastocyst from the zona pellucida was studied in 1441 eggs from 134 animals in which the time of ovulation had been controlled precisely by gonadotrophin injection. Observations were also made on the rate of egg passage through the Fallopian tubes, on the process of denudation, and on the increase in numbers of spermatozoa associated with the zona pellucida.Eggs may be penetrated and activated within three hours of mating or insemination close to the time of induced ovulation. A decondensation and swelling of the chromatin is seen very soon after incorporation of the sperm head into the vitellus, and central apposition of the pronuclei occurs three to five hours later. The male pronucleus is slightly larger than the female, and a portion of the flagellum is frequently closely associated with it until late syngamy. Cleaved embryos can be recovered within 14 to 16 hours of sperm penetration, but the two-celled stage lasts only six to eight hours compared with 20 to 24 hours for the four-celled stage. Embryos enter the uterus at the latter stage approximately 46 hours after ovulation. Morulae of 16 to 32 cells can occasionally be observed late on the third day of development, and blastocysts are present on the fifth day. However, the zona pellucida is not shed until the sixth day, after which the trophoblast commences the massive elongation characteristic of this ungulate blastocyst.

Notes: During the postnatal development of the submandibular gland, the stimulation of DNA synthesis and mitosis by a single injection of isoproterenol, measured as the percentage of labeled cells in radioautographs, was dependent on the age of the rat. The drug had no effect on the proliferative activity in two day old rats, but stimulated DNA synthesis in older (7-42 day old) animals. In general, the degree of stimulation was directly related to the proportion of acinar cells and inversely related to the proliferative activity in the gland of control rats. An analysis of various cell types revealed that the stimulation of DNA synthesis in the gland was essentially restricted to the acinar cells in rats older than 14 days of age. In seven day old rats, the acinar cells were not stimulated, but their precursors, the proacinar cells, the terminal tubule cells and the intercalated duct cells were stimulated to synthesize DNA by isoproterenol. This suggested that isoproterenol had an effect on the transformation of precursor cells to acinar cells.

Notes: The postnatal differentiation of acini in the submandibular glands of 2-42 day old rats given 3H-thymidine was studied by using radioautographs prepared from Epon-embedded, PAS and iron hematoxylin stained sections. The changes in morphology, population size and proliferative activity of various cell types in the gland were analyzed. At two days of age, rudimentary secretory units, designated as terminal tubules, were located at the end of the duct system and consisted of three cell types: (1) terminal tubule cells (30.7%) with darkly-stained granules, (2) proacinar cells (23.6%) with large, lightly-stained granules, and (3) acinar cells (1.6%) with PAS-positive granules. The proacinar cells, which underwent mitosis, disappeared within the first two weeks of life. The terminal tubule cells increased in number between 2 and 14 days of age, but became less numerous thereafter and disappeared by six weeks. Concomitantly, the number of acinar cells increased linearly with age and at a much greater rate than that of intercalated duct cells. Yet the rate of proliferation of acinar cells was comparable to that of intercalated duct cells. The overall proliferative activity in the gland decreased with age, and was inversely correlated with the relative frequency of acinar cells in the gland. On the basis of above data, it is postulated that, during the formation of acini from terminal tubules, acinar cells have a dual origin: they arise from proacinar cells during the first one to two weeks and from terminal tubule cells between two and six weeks of age.

Notes: A staining technique, in which basic fuchsin, methylene blue, and Azure II is applied to 0.5 μ sections of striated rat muscle embedded in epoxy resin, has given sufficient differentiation of five nuclear types found in the muscle fascicle to warrant its use as a valid method for identifying satellite cells with the light microscope. The validity of this technique was assessed by studying serial thin and thick sections of denervated rat hind limb muscles. Nuclei “typed” light microscopically were examined under the electron microscope to determine the type of cell in which they were located. This stain technique was then applied to determine the effect of denervation on the satellite cell population of the tibialis anterior and extensor digitorum longus. In control muscle of 200 gm rats, satellite cells represented 2% of the total nuclear population. Two and three weeks after denervation they accounted for 6% and 12%, respectively. In 800 gm rats, satellite cells accounted for 0.7% of the total nuclei found in the normal muscle. Denervation increased the percentage to 3% (at 2 weeks) and 5% (at 3 weeks). Paired satellite cells were infrequently observed; however, in 0.5 μ sections a significant number of satellite cells were found to be less than 0.7 μ from a myonucleus of the same fiber. A model is proposed to explain the increase in satellite cells following denervation.

Notes: Hypertrophic scar, mature scar, normal skin and granulation tissue were studied by transmission (TEM) and scanning (SEM) electron microscopy for characteristics and differences in fine structure, especially the collagen filaments and their physical association with each other and with interstitial components of the ground matrix.The shape of the collagen filaments is irregular and angular in granulation tissue, irregular to ovoid in hypertrophic scar, ovoid to round in mature scar, and round in normal skin. The mean diameter of the collagen filaments measures approximately 440 Å in granulation tissue, 600 Å in hypertrophic scar, 1000 Å in mature scar, and 1050 Å in normal skin.Interstitial filaments are prominent in hypertrophic scar by TEM. In nodular areas where collagen is examined in cross section the interstitial filaments often appear to interconnect long chains of collagen filaments. The interstitial filaments are not observed by SEM. Rather, by this method of observation, the demis of hypertrophic scar is seen as a homogeneous matrix, and individual collagen filaments are not observed.It is suggested that the hypertrophic scar is characterized by an unusually firm intercollagen binding by interstitial filaments, which are probably protein-polysaccharides of the ground matrix. This relationship could account for the clinical quality of extreme hardness of the scar, and might also suggest an aberration important in the etiology of the scar.

Notes: The granule-containing cells in the wall of the arch of the aorta proximal to its union with the ductus arteriosus in young chicks were examined by electron microscopy. These cells contain many electron-opaque vesicles, about 1500 Å in an average diameter, and show basically similar cytological characteristics to the granule-containing cells described in autonomic ganglia, around the abdominal aorta, and in the carotid body of mammals. Occasionally the cells are in close apposition to smooth muscle cells, fibroblasts or endothelial cells. Other surfaces of the granule-containing cells are partly covered by satellite cells. Synapses are rarely found on the granule-containing cells in the tunica media of the aorta.A few bundles of elongated cells which enclose several nerve fibers in the cytoplasm penetrate perpendicularly into the tunica media of the aorta. In these bundles are also a few granule-containing cells. Three types of nerve endings terminate on the granule-containing cells; that is, endings with small clear synaptic vesicles, with small cored vesicles, and with large cored vesicles. In addition, presumptive afferent nerve endings are found in the bundles. They show a variable diameter along their tortuous courses and contain numerous mitochondria.

Notes: Because of a major (Ag-B) histoincompatibility, organs transplanted from Lewis (LE) to Brown Norway (BN) rats are acutely rejected. This immunological rejection can be prevented by inoculating BN rats at birth with (BN × LE)F-1 hybrid cells. However, the source of these cells is important since only those derived from the bone marrow are effective in inducing tolerance of LE skin grafts whereas both marrow derived cells as well as those originating from the lymph nodes can induce tolerance of LE hearts. The present study was undertaken to compare the efficacy of cells derived from the bone marrow and the lymph nodes of (BN × LE)F-1 rats to induce unresponsiveness to LE neurons in BN recipients. In untreated rats, all neurons in sensory (vagal nodose) and sympathetic (superior cervical) ganglia transplanted from LE rats to the anterior chamber of the eye or implanted into the sternomastoid muscle of BN recipients were rejected within 35 days. However, when neonatal BN rats were inoculated with adult (BN × LE)F-1 hybrid bone marrow or lymph node cells and challenged as adults with LE ganglia grafts many neurons survived beyond 100 days. This result demonstrates that tolerance of Ag-B incompatible neurons can be achieved with either bone marrow or lymph node cells. Moreover, since tolerance can be produced in rats exhibiting major or minor histoincompatibilities, this method of immunosuppression offers one way of preventing neuronal rejection which occurs acutely in Ag-B incompatible and chronically in Ag-B compatible ganglia homografts.

Notes: The ruthenium red staining technique of Luft ('71b) was utilized in an electron microscopic investigation of developing and adult rat lung. Electron-dense deposits of ruthenium red-positive material were observed on all exposed surfaces of the tissue block, regardless of the stage of development. In the more central areas of the block, sites of ruthenium red binding changed with age. In early prenatal lung (days 16 to 20) dense accumulations of ruthenium red-positive material were found in association with the basement membranes of endodermal epithelial cells. Ruthenium red binding was also observed between adjacent epithelial cells; however, their luminal surfaces were negative. The main intracellular site of ruthenium red binding in intact cells was the lamellar body of the developing type II pulmonary epithelial cells. By day 21 of development, accumulations of granular product were observed in association with most lamellar bodies, as well as on epithelial cell luminal surfaces. Ruthenium red binding in postnatal tissue decreases with increasing age. By the second postnatal week, the predominant site of binding is the luminal surface of the type I and type II pulmonary epithelial cells. When compared to fetal and early neonatal stages, adult rat lung has a still more limited distribution of ruthenium red-positive material. Changes in the distribution of ruthenium red-positive material correlate with numerous morphologic and biochemical events in rat lung development.

Notes: The course of reinnervation and the effects of denervation and immobilization on muscle development were examined during the regeneration of minced muscle in anurans. Reinnervation occurs in the second week, at the time of myotube formation and differentiation. At the end of thirty days, nerves are plentiful and extensively distributed within the regenerating muscle. Cholinesterase activity within the regenerated muscle cannot be demonstrated at this time. Denervated regenerates develop normally during the first two weeks, but, thereafter, the young muscle fibers exhibit signs of degeneration and retarded growth. Denervated regenerates become fibrotic and contain few muscle fibers at the end of four weeks. Regenerates from muscles denervated prior to mincing show an accelerated appearance of presumptive myoblasts in the first week, but despite this precocious development, these denervated regenerates become regressive. On the other hand, the effect of disuse on muscle regeneration is not detrimental; the fibers of reinnervated but immobilized regenerates develop normally and do not become degenerative. These results suggest that nerves are unnecessary for the early myogenic processes of proliferation and fusion, but are essential to later stages of growth, maturation and maintenance of the regenerated muscle fibers.

Notes: The satellite cell population in mouse lumbrical muscle is quantitated at ages 7, 14, 21 and 30 days. Satellite cell nuclei comprise nearly 30% of the nuclei within the fiber basal lamina in the youngest animals studied. Growth is accompanied by a rapid decrease in the percentage of satellite cell nuclei. This is not accounted for by the increase in myonuclei, but rather there is an absolute decrease in the number of satellite cells. This loss in satellite cells occurs in spite of their high rate of division and is explained by a high percentage incorporation of the daughter cells of satellite divisions. It is further suggested that the percent incorporation of available cells decreases with age.

Notes: RivanolR, a fluorescent ethoxy derivative of acridine, interacts at different pH's with both glycosaminoglycans and proteins. The present study utilizes the specific interaction of RivanolR with acidic substances of the ground substance for histochemical studies of the cartilage matrix. This stain was applied to newborn mouse epiphyseal cartilages which were either unextracted or dissociatively extracted by graded concentrations of guanidinium chloride (GuHCl) from 0.5-3.0 M for four days at 25°C. Routinely prepared sections were then stained (0.1% solution) for two minutes at pH's ranging from 2.2-11.2. Stainability of the interterritorial matrix as well as the inner halo zone and outer corona zone of the lacunar matrix varied with pH. Whereas the interterritorial matrix decreased in stainability with rising pH, the halo and corona persisted in stainability up to pH 10.7. Dissociative extractions using GuHCl revealed the unextractable nature of the inner halo zone as well as the extractable nature of the corona above 1.0 M GuHCl concentration. Anionic sites on polyelectrolytes such as glycosaminoglycans are known to stoichiometrically bind many cationic dyes. The precise localization of stain-reactive glycosaminoglycans or proteoglycans in the region of the perichondrocytic matrix by RivanolR supports prior observations using other cationic stains. Our data demonstrates that RivanolR enables one to visualize the unique perichondrocytic matrix which may be interpreted to be both chemically and morphologically a “matrix within a matrix”.

Notes: Ovarian and uterine morphological changes were examined in the maturing Holtzman rat, ages 22-40 days, using routine histological procedures. These findings were then correlated with serum follicle stimulating hormone (FSH) and luteinizing hormone (LH), in an effort to trace the sequence of events involved in the onset of puberty (i.e., the initiation of cyclicity) which occurred most consistently in our rats at 38 days of age. Ovaries exhibited no significant weight increases prior to day 36. However, microscopic changes became apparent as early as day 30, and continued to day 38, the day of the gonadotropin surge. During this time interval, the proportion of large type 6-7 (potentially estrogen secreting follicles) increased dramatically relative to non-antrum containing follicles. An increasingly hypertrophied and well differentiated theca interna of the larger follicles was also characteristic of this age interval. Closely paralleling the sequence of follicular maturation, quantitative and qualitative increases in all layers of the uterus occurred. As early as day 32, the luminal epithelium had increased some three to four-fold over earlier age groups. Similarly, the stromal endometrium and myometrium increased significantly at this time. Further increments occurred through day 34, with a leveling off at this time.Serum FSH showed no significant increases prior to day 38, at which time levels increased some two-fold over previously existing levels. In contrast, LH remained tonic until days 34 and 36, at which time subthreshold elevations occurred. On day 38, LH rose some 40-fold over pre-existing levels. Serum prolactin followed a similar pattern; levels became detectable at 33 days of age with marked elevations seen on day 35 and on day 38 of age.From quantitative and qualitative analysis of ovarian and uterine morphology with subsequent correlations to serum gonadotropins over the maturing process, we conclude that the ovary possibly acts as a “Zeitgeber” for the gonadotropin surge and ovulation.

Notes: Cationized ferritin was used to analyze the surface charges on the luminal epithelial cell membranes of urinary bladders from toad (Bufo marinus), bullfrog (Rana catesbiana), turtle (Pseudemys scripta and Clemmys caspica), and tortoise (Geochelone carbonaria and Testudo graeca). The labeling, done at a physiological pH on fixed or unfixed bladders, revealed differences in the distribution and density of negative charges along the luminal membrane surfaces. The epithelial surface of toad bladder did not label with cationized ferritin. Frog bladder labeled lightly and the labeling pattern varied between cell types. The epithelial membrane surfaces of reptile bladders were heavily labeled, in contrast to amphibian bladders. Luminal surfaces from fresh water turtles were not as heavily labeled as those from land tortoises. The degree of labeling varied from cell type to cell type in all reptile bladders except Pseudemys scripta. An analysis of the degree and pattern of labeling by cationized ferritin in bladders of all species studied might reflect a difference in the nature of the glycocalyx of a particular membrane, the presence or absence of negative surface charges or their availability (i.e., interference by mucus), and/or the nature of the chemical groups comprising the surface structure of the membrane.

Notes: Ependyma from random sites of lateral, third and fourth ventricles including the aqueduct in five adult human brains was examined by transmission electron microscopy. In all the specimens studied, cilia were present in variable numbers in the ependymal cells. Our study thus establishes that there is widespread presence of cilia in the ependymal cells of the ventricular system in the adult human brain.

Notes: The soleus muscle is widely used in biochemical and physiological investigations as an example of a slow-twitch red muscle, and it has been assumed, for the most part, that it consists of a homogeneous population of either red or intermediate fibers. In the present study, the cytological composition of this muscle was examined in four commonly studied species, namely the rat, guinea pig, rabbit and cat. Using the form and distribution of mitochondria as the principal criteria for identification, two distinct types of muscle fibers can be recognized in the soleus of the guinea pig and rabbit as well as the rat. The soleus muscle is therefore not homogeneous in either species. Preliminary observations suggest that the soleus of the cat is likewise not homogeneous. In addition, although the fibers resemble red and intermediate fibers in other skeletal muscles, the resemblance is only superficial. In the two fiber types of the rat and guinea pig soleus, the Z line is characteristically wide, and therefore, based on this criterion, the fibers are not equivalent to either the red or intermediate fibers of other muscles.

Notes: Normally, the size of pancreatic acini is remarkably decreased after birth in the rat.Administration of water or milk on day 21 of gestation resulted in decreased acinar size a day later in intact fetuses and in fetuses decapitated immediately after administration of water or milk. The same treatments of premature newborn rats obtained by Caesarean section on day 22 of gestation induced similar effects a day later On the other hand, in starved Caesarean newborn rats, there were no histologic changes in acini. In spontaneous newborn rats which were allowed to suckle maternal milk and then starved for one day, there was an increase in acinar size as compared with that of 2-day-old normal rats.These results suggest that the fetal pancreatic acini at least near term (on day 21 of gestation) can respond to some signals conveyed from digestive tracts which have responded to exogenous stimuli, that the brain during fetal days does not play any role in digestive tract-pancreatic acini interrelations in secretion of zymogen granules and that the neonatal decrease in acinar size is caused by the intake of maternal milk.

Notes: In frozen sections and whole mount preparations of the normal soleus, diaphragm, or intercostal muscles of the rat, myoneural junctions of different AChE and silver staining intensities were regularly observed. Muscle fibers of different diameters showed end-plates of varying staining intensities. No correlation was found between a certain staining intensity and diameter of the end-plates or between muscle fiber diameters and the ratio of pale to strongly stained end-plates. There was, however, a tendency for the smaller muscle fibers to have end-plates of smaller mean diameter than those in the larger muscle fibers.

Notes: The effects of trypsin, chymotrypsin, papain, pronase, cartilage protease and hyaluronidase on the staining of fresh epiphyseal cartilage in 0.01% toluidine blue at pH 4 was studied. Treatment with these enzymes resulted in a loss of the β- and γ-metachromatic granules in the cells, and an intensification of the staining in the matrix of the lower hypertrophic zone. Treatment with collagenase also resulted in a loss of the β- and γ-metachromatic granules, but did not appreciably intensify the staining of the matrix. Carboxypeptidase A, ribonuclease and bovine serum albumin, globulins, and globin had little or no effect.

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

Notes: The long antennal flagellum of Neoconocephalus ensiger is covered with many sharp-tipped hairs that appear to be non-innervated; thick-walled chemoreceptors, that may also have a tactile function; thin-walled chemoreceptors of several kinds and coeloconic chemoreceptors. All of the chemoreceptors are innervated by small groups of neurons. The first flagellar subsegment is unusual in that it bears a small protuberance on its latero-ventral surface. This marks the site of the attachment, internally, of a scoloparium containing about eleven scolopales in which the dendrites of some 23 sensory neurons terminate. The most distal subsegment lacks the scoloparium reported earlier for the grasshopper. No conspicuous difference between the antennae of males and of females was found.

Notes: The antennae of two species of thrips, Bagnalliella yuccae (Hinds) and Frankliniella tritici (Fitch), have been examined with the light and electron microscopes. The antennal flagellum of both species is provided with tactile hairs, thick-walled chemoreceptors and thin-walled chemoreceptors. In addition, B. yuccae, but not F. tritici, has a single coeloconic chemoreceptor on the dorsal surface of the pedicel. Observations were made on the fluids in the lumen of the antennae of E. yuccae in the living insect. The movement of the fluids probably has an important physiological significance.

Notes: Gonadotrophic cells in the pars distalis of Anolis carolinensis often contain juxtanuclear concentrations of filaments with diameters intermediate in size (approximately 100 Å) between microtubules and microfilaments. Their size and their substructure, which gives them a tubular appearance when they are displayed in cross-section, appear to place these filaments in the “intermediate filament” category (Ishikawa et al., '68). In their juxtanuclear position in the intact animal, the intermediate filaments are collected in randomly-oriented tangles. In castrated specimens of Anolis, gonadotrophs degranulate and elongate. During this elongation, increased numbers of microtubules appear in orientation parallel to the long axis of the cell, and the 100 Å filaments reassemble in rod-like masses oriented parallel to the microtubules. This apparent distributional interaction may facilitate the elongation of the cell. Intimate physical associations between the intermediate filaments and secretory granules suggest that the filaments may act in the movement of the granules during the processes of degranulation and secretion.

Notes: The cervicothoracic muscles of nymphal and adult Euborellia annulipes (Lucas) are described, the former for the first time. In the adult, eight new muscles are identified, while the nymphs possess a further seven muscles that disappear at maturation or before. Otherwise the same muscles occur in nymphs as in adults, though some nymphal muscles are less clearly separated from one another than their adult homologs. The attachment sites of certain muscles show a number of slight differences between nymphs and adults. The work emphasizes the necessity of taking the immature musculature into account in assessing the muscular pattern represented in an insect order.

Notes: The morphological features of the hemocytes of the crustacean Ligia exotica are similar to hemocytes of insects and millipedes. Jones system of hemocyte classification is extended to crustacean hemocytes. As in insects, seven classes of hemocytes, identified as prohemocytes, plasmatocytes, granular hemocytes, cystocytes, oenocytoids, spherule cells and adipohemocytes, occur. The prohemocytes can be subdivided into five categories that probably represent the precursor of major cell types. The structural and chemical features of other major cell classes are distinct and support the concept of Jones ('62) that these types might have different lineages and might not be capable of transforming into one another. Some of the prohemocytes, plasmatocytes and granular hemocytes are amoeboid. Cystocytes do not bring about any visible plasma coagulation similar to their counterpart in millipedes. Oneocytoids and adipohemocytes are rare. Plasmatocytes, cystocytes and oenocytoids occur in conglomerates, the significance of which is discussed. The cell types are compared with those of the hemocytes of other crustaceans. It is suggested that the nomenclature based on morphological characters is more suited for crustacean hemocytes than a nomenclature based on behavioural and physiological characters.

Notes: Some of the cytological characteristics of the hemocytes of the scorpion, Palamnaeus swammerdami, were studied. The morphological features of the arachnid hemocytes were observed to be similar to those of hemocytes of insects, millipedes and isopods. Jones' system of hemocyte classification was extended to the arachnid hemocytes. The six classes of hemocytes indentified in the scorpion correspond to prohemocytes, plasmatocytes, granular hemoocytes, cystocytes, spherule cells and adipohemocytes of insects. A cell type comparable to oenocytoids of insects and crustaceans is absent. The prohemocytes can be subdivided into four categories that probably represent the precursors of the major cell types. The cytological characteristics of the major cell classes and the occurrence of the miniatures of some of these major cell types support the concept of Jones (62) that these cell types might have different cell lineages and might not be capable of transforming into one another. Some of the prohemocytes, plasmatocytes and granular hemocytes were amoeboid. The nature of the granules and the vacuoles of plasmatocytes and granular hemocytes were compared with the granules and vacuoles of corresponding hemocytes of other arthropods. Cystocytes did not bring about any visible coagulation similar to their counterparts in millipedes and crustaceans. Plasmatocytes, granular hemocytes and spherule cells were observed to occur in conglomerates. The cell types noted in the present study were compared with the hemocytes of other arachnids.

Notes: Transmission and scanning electron microscopic studies demonstrate the stimulatory effect of synthetic salmon calcitonin on the fine structure of fibroblasts and on collagen formation in cutaneous wounds experimentally induced in rabbits. Long-term administration of calcitonin enhances fibroblast growth and collagen synthesis. The fibroblasts hypertrophy and exhibit a highly developed rough endoplasmic reticulum (RER), several polyribosomes, large nuclei, hypertrophic Golgi complex, and many dense granules and lysosomes. Mitochondria are elongate and ramify; intracellular as well as extracellular synthesis of collagen increases. Fibrils appear tightly packed, in large heaps or spicula, with a characteristic periodicity and striation.Scanning electron micrographs of topography and relationships with collagen fibers and fibrils and cells surface changes demonstrate an extensive network of fine fibrils between collagen fibers, marked ruffling of cell membranes as well as numerous blebs on the cell surface. The latter are significant in collagen formation and egestion.

Notes: An arbitrary classification scheme is presented for the thirteen distinct types of secretory cells distinguished within the central nervous system of Dermacentor variabilis by several specific and general neurosecretory staining techniques. Comparisons to classic arthropod neurosecretory cell types are made and the histochemical implications of the chromophilic response of various secretory products are discussed. Dermacentor cells of Types I, VII, IX and X may be considered neurosecretory on the basis of intracellular elaboration and discharge of secretory product. Type II, III, IV, V, VI, XI and XII cells are considered as putative neurosecretory cells although secretory products were detected only within the perikarya. The large Type XII cells are also similar to motor neurones reported from other arachnids. Cells of Types VIII and XIII appear to be glial elements. The secretory products of Type XIIIA are distributed within trabecular processes in the subperineurium. These products may play a trophic role or they may have some endocrine function as a form of “gliosecretion”.

Notes: Sperm enter the anterior vas deferens individually in the spider crab male. There they become surrounded by secretion products from the cells of the vas deferens, and are compartmentalized into spermatophores of varying size. The anterior vas deferens can be divided into three regions. The epithelium of the anterior vas deferens varies regionally from low to high columnar. The cytoplasm contains vast arrays of rough endoplasmic reticulum and Golgi complexes but few mitochondria. Intercellular spaces contain septate junctions, gap junctions and vesicles.Once the spermatophores have been formed in the anterior vas deferens, they are moved posteriorly to the middle vas deferens where they are stored and surrounded by seminal fluids. The epithelial cells of the middle vas deferens contain large amounts of rough endoplasmic reticulum and Golgi complexes. Numerous micropinocytotic vesicles appear, forming at the cell surface and within the apical cytoplasm. Their suggested function is the resorption of secretion products of the anterior vas deferens which initiated compartmentalization of the spermatozoa into spermatophores.The posterior vas deferens functions primarily as a storage center for spermatophores until they are released at the time of copulation. Seminal fluid surrounding the spermatophores is produced in this region as well as in the middle vas deferens. The cells of this region contain vast arrays of vesicular rough endoplasmic reticulum and Golgi complexes. The cells are multinucleate. Microtubules are numerous throughout the length of the cells and appear to insert on the plasma membrane.

Notes: Rostral pores are epidermal invaginations which occur on the internarial region of most chelonians. Representatives of all Recent chelonian families and 67 of the 74 extant genera were examined grossly and/or histologically. Pores are absent only in the families Carettochelyidae, Cheloniidae, and Dermochelyidae. The number and microscopic structure of pores vary markedly within and between taxa. Morphological data suggest that rostral pores could function in mechanoreception. The possible origin and evolution of rostral pores are discussed in the context of other chelonian integumentary speializations.

Notes: The termite gut flagellates are of interest because of their unusual motile organelles, their ability to digest cellulose, and their symbiotic relationship with prokaryotes inhabiting the insect gut. This report provides a detailed ultrastructural description of Pyrsonympha from the hind-gut of Reticulitermes flavipes.The motile axostyle is composed of 2,000-4,000 microtubules connected by cross-bridges. At its anterior end, the axostyle is associated with a “primary row” of microtubules which is associated with a fibrous network. The “primary row” is embedded in a large mass of amorphous, electron-dense material occupying the furthest anterior end of the cell. The basal bodies of the eight flagella are also embedded in this presumptive microtubule-organizing center. The flagella are associated with the cell surface throughout their length. Isolation and reactivation of the axostyle has demonstrated that although ATP dependent motility is inherent in the structure of the axostyle, its proper control may be mediated by the attachment of the axostyle to structures at the anterior end of the cell.Pyrsonympha lacks morphologically distinguishable mitochondria and Golgi complexes. The cell surface is covered by unique, previously underscribed, tubular specializations. Symbiotic microorganisms are observed associated with the cell surface and within the cytoplasm.Wood particles are taken up from the gut fluid by large phagocytic vacuoles formed at the posterior end of the cell. Even during the process of breakdown, the wood is always enclosed within the membrane of the phagocytic vacuole.The Pyrsonympha from Reticulitermes flavipes are not attached to the lining of the hind-gut and do not contain an attachment organelle, unlike the Pyrsonympha from other species of Reticulitermes.

Notes: Basicranial anatomy of mammalian carnivores is significant in the determination of carnivore evolution. One of the least understood yet most often studied features of the basicranium is the auditory bulla, a bony capsule enclosing the middle ear. Although previously believed to be formed by a tympanic bone alone, or by tympanic and entotympanic, it is shown here that the carnivore bulla is formed by three and in some cases four ontogenetic elements: tympanic, rostral entotympanic, caudal entotympanic(s). These elements in Carnivora appear to correspond to bulla elements discovered over 50 years ago by Van der Klaauw in representative species of several other orders of mammals.Increased auditory sensitivity appears to have been attained in various carnivore lineages by increase in the volume of the middle ear cavity, principally by hypertrophy of the caudal entotympanic, but also by different yet less common anatomical strategies such as invasion of the mastoid bone by the middle ear space. Five basic types of bulla among living Carnivora can be recognized, based largely on the relationship of the caudal entotympanic to the other bulla elements.Closely associated with the bulla in the auditory region are the median and promontory branches of the internal carotid artery. These branches exhibit a precise relationship to the bulla elements, particularly the rostral entotympanic. The promontory branch is much reduced or completely lacking in all living carnivores. Reduction or loss of the median branch is explained as the result of the development of arterial retia on the anastomotic artery in the orbital region. Reduction of the median branch is particularly characteristic of the aeluroid Carnivora, in which a greater proportion of the cerebral blood supply passes to the brain in the external carotid artery via the anastomotic branch, and is cooled in the orbital region by a countercurrent heat exchange mechanism formed by arterial retia closely associated with venous blood in surrounding sinuses. The arctoid and cynoid Carnivora are characterized by only rudimentary development of retia along the anastomotic artery, and the median branch is much better developed than in the aeluroids. Among arctoids, ursids parallel the aeluroids in the development of a countercurrent mechanism but employ the median branch of the internal carotid rather than the anastomotic branch of the external carotid artery.Bulla structure and nature of the carotid circulation in the auditory region can be determined from fossil Carnivora as well as for living forms. This study attempts to define basicranial anatomical patterns characteristic of living Carnivora which then can be used to trace the evolution of lineages in the fossil record.

Notes: Mature mouse and cat peripheral nerve fibers have been examined in vitro by time-lapse photography. Some Schmidt-Lanterman clefts which were open at the start closed later; other were seen to open and then to close, some of them more than once. The implications of these movements are considered, especially in regard to the question of the passage of materials from the endoneurial connective tissue spaces to the axon.Myelin movements other than those occurring at the Schmidt-Lanterman clefts consisted primarily of the development and frequent regression of indentations of the myelin sheath. A single evagination was seen to develop and then to recede. These myelin movements suggest that previously described invaginations and evaginations of the myelin sheath, including flaps of “redundant myelin”, are not static but rather that they are in a state of movement, forming and regressing at intervals.The possible functional significance of the development and regression of myelin sheath indentations in relationship to axoplasmic flow is discussed.

Notes: The gecko ear was studied in 36 species belonging to 24 genera. This receptor has attained an advanced level of structure and performance in this group of lizards, but there are many variations among species. To a large extent these variations follow subfamily lines as represented in Kluge's system of classification.Brief consideration is given to features of the outer and middle ear, but chief concern is with inner ear structures and their relations to auditory sensitivity as represented by the cochlear potentials.The auditory papilla is segmented, with a dorsal portion whose hair cells have their ciliary tufts attached to a tectorial membrane, and a ventral portion in which these cells form tow assemblages, one with tectorial connections and the other with connections to a line of sallets.The dorsal segment varies greatly in length and in the form of ciliary orientation. In Eublepharinae and most Gekkoninae the ciliary orientation is unidirectional, and the degree of sensitivity relates to the length of this segment. In Diplodactylinae and Sphaerodactylinae the orientation is bidirectional, and this segment functionally hardly differs from the ventral segment.Auditory sensitivity as measured in terms of the cochlear potentials shows close relations with subfamily groupings, except for the Gekkoninae in which considerable diversity is found.The evidence from structural differentiation, along with that derived from the forms of the cochlear potential functions, leads to the suggestion that these ears possess a high degree of pitch discrimination and capability for the analysis of complex sounds.

Notes: The authors describe the spermiogenesis of Polyxenus lagurus, a diplopod, in the male genital ducts and the transformations the spermatozoon successively undergoes in the spermatheca.The spermatozoon in the male genital ducts looks like a little barrel devoid of centriole and of any kind of rudimentary flagellum whatever. The organelles are markedly modified; cross sections present an elongated, flattened nucleus, an X-shaped body running parallel to it on the opposite side and two longitudinal mitochondrial strips interposed between them. The rest of this barrel-shaped spermatozoon is filled with peculiar Golgi formations, the spongy chambers, which open outwards through little vents.In the spermatheca the spermatozoon is quite different: it is shaped like a long ribbon. The basic structure of the spermatozoon is formed by the double folding of part of the cortical layer of the barrel-shaped spermatozoon. On the central part of this endo-skeleton are longitudinally ranged the nucleus and the acrosome flanked on both sides by a thread of mitochondria. Even in this phase the sperm has no flagellum.

Notes: Several secretory and nonsecretory enzymes were localized histochemically in the main venom gland of 13 viperid snakes. All secretory cells show the intracellular oxidative enzymes succinate dehydrogenase and monoamine oxidase. The granular reactions obtained for both enzymes resemble mitochondria in distribution. Distinctive cells with a very high succinate dehydrogenase activity are dispersed among the secretory cells of all species except Atractaspis.Nonspecific acid phosphatase activity is found in the supranuclear region of the secretory cells in species that do not secrete this enzyme and throughout the cytoplasm in snakes that secrete the enzyme. Nonspecific alkaline phosphatase activity occurs in the secretory cells of those snakes whose venom shows this activity. Leucine amino peptidase (aryl amidase) activity is found in the venom and in the secretory cells of all the species.In Vipera palaestinae both the venom and the secretory cells of the main venom gland contain nonspecific esterase, L-amino acid oxidase and phosphodiesterase activities. The localization of phosphodiesterase and L-amino acid oxidase do not show major differences between glands at different intervals from an initial milking.Adenosine-monophosphate phosphatase activity is localized in the supranuclear region of the secretory cells in the glands of Vipera palaestinae and Aspis cerastes. Its activity is found in the venom of Aspis only.

Notes: The three dorsal ocelli of worker honeybees have been studied by light and electron microscopy. Each ocellus has a single flattened spheroidal lens and about 800 elongated retinular cells. Retinular cells are paired and form a two-part plate-like rhabdom between their distal processes. Each rhabdomere comprises parallel microvilli projecting laterally from the apposed retinular cells. Primary receptor cell axons synapse within the ocellus with ocellar nerve fibers of two different calibers. Each ocellus has eight thick fibers ca 10 m̈m in diameter and several thinner ones less than 3 m̈m in diameter. Fine structural evidence suggests that retinular axons end presynaptically on both types of ocellar nerve fibers. Since all retinular cells apparently synapse repeatedly with the thick fibers this involves a convergence of about 100:1. Thick fibers always terminate postsynaptically within the ocellus while thin fibers terminate presynaptically on other thin fibers, thick fibers or retinular axons. Structural evidence for synaptic polarization indicates that retinular cells and thick fibers are afferent, thin fibers efferent. Thus complex processing of the ocellar visual input can occur before the secondary neurons of the three ocelli converge to form the single short ocellar nerve which runs to the posterior forebrain.

Notes: Ampullary receptor organs of African mormyrids consist of a cavity beneath the epidermis. The wall of the cavity contains embedded receptor cells and two types of supporting cells. A canal extends from the cavity to an opening at the surface. The lumen of the canal and the ampulla are filled with a jelly-like material and dense cylinders apparently secreted by two types of supporting cells. Flattened cells of the canal wall are joined by occluding junctions. Synapses between receptor cells and the afferent nerve fiber are characterized by a presynaptic dense body, but presynaptic vesicles were not observed. Degenerating receptor cells are occasionally seen among normal receptor cells in the base of the organ.

Notes: This paper examines the effect of early thymectomy on the subsequent development of lymphoid tissues in the toad, Xenopus laevis. At the time of thymic removal (8 days post-fertilization) all the lymphoid organ anlagen are at a rudimentary state of differentiation and contain few, if any, small lymphocytes. Despite the absence of any thymic tissue all thymectomized animals grew normally.Thymectomized larvae developed relatively normal lymphoid organs. However, lymphoid depletion was apparent in the splenic red pulp and in the pharyngeal ventral cavity bodies. Examination of the lymphoid organs of post-metamorphic Xenopus revealed reduction in spleen size following thymectomy. Lymphoid depletion was evident in the splenic red pulp of many thymectomized toadlets and reduction in proportion of white to red pulp was also noted in a few of these animals. Absence of the thymus had no apparent effect on the histology of the other lymphoid organs examined.

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 surface structures of the antennular flagella of Pagurus alaskensis are described in detail. Attention is directed towards the surface morphology of two types of possible sensilla: (1) exoskeletal pores (1.0-3.0 μm in diameter); (2) setae of various kinds. In addition, small (0.1-0.2 μm) pits occur in the exoskeleton which are not considered to be sensory in function. The exoskeletal pores are found at fairly specific locations on both the inner and outer flagella, particularly on the short segments of the outer flagella. Neither the inner nor the outer flagella are bilaterally symmetrical with respect to their setal armature. On the outer flagellum six groups of setae may be distinguished: lateralmesial; dorsal; ventral; accessory; aesthetasc; setae of the distal segment. On the inner flagellum setae of the mesial and lateral rows form distinctive groups. The morphology, orientation and locations of all the flagellar setae are defined and where possible the numbers of the various morphological types within the specific setal groups are given. It is noteworthy that many setal types have obvious apical pores and yet no pores could be found in the chemoreceptive aesthetasc setae. The functions of the various setae are discussed in relation to their topographical position and to existing electrophysiological and behavioral data. Some suggestions are made about future experiments to demonstrate the central connections of specific sensilla or groups of sensilla and to show their significance in the whole animal.

Notes: Blood vessels in Nereis japonica were studied by electron microscopy. It was found that blood vessels regardless of location were similar in the basic organization of the basal lamina and the usual presence of collagen fibrils on the vessel wall. Differences arise, depending on whether the outside of the basal lamina is covered by peritoneal cells, by gut epithelium, or by epidermis. These relate to the location of the vessels in mesenteries, gut or epidermis, but do not reflect basic structural differences in the vessels themselves. Furthermore, it was concluded that true endothelial cells do not exist in the circulatory system of Nereis japonica and that, in this respect, the system is essentially different from that of vertebrates, in which endothelial cells line the vessels of a closed circulatory system. These considerations lead to the further conclusion that the vascular lumen in Nereis is essentially interstitial space and that the system, which has been known as a typical “closed” circulatory system in annelids, is actually an open circulatory system. Peritoneal cells covering the walls of internal vessels show various degrees of muscular differentiation and those possessing myofilaments may be called “myomesothelial cells.”

Notes: Allografts of skin were observed in Chelydra serpentina. The response to these grafts was modified by a previous transplantation of a limb bud at an early embryonic stage. When the same donor was used for all transplants, the first skin graft was accepted by the host. A second skin graft, however, was rejected at about the rate of a simple first set allograft of skin. The animals were conditioned by the embryonic limb graft; this embryonic graft can be undergoing rejection at the same time a first set skin graft from the same donor was being accepted. The tolerance induced by the embryonic graft was sepcific for its donor.

Notes: As part of program of research into insect cellular immunity, an integrated light and electron microscopic study of the hemocytes of seven members of the Order Dictyoptera has been made. In fresh hemolymph, five cell types, the prohemocytes, plasmatocytes, granular cells, spherule cells and cystocytes, are easilv distinguished. However, in thick Araldite sections and in thin sections in the electron microscope it is sometimes difficult to identify the various cell types. The reasons for this difficulty are discussed.Granules with a microtubular substrcture are found in the plasmatocytes, spherule cells and cystocytes. In the plasmatocytes these granules have a different ultrastructure than those in the spherule cells and cystocytes. The in vitro fragility of these granules in both the spherule cells and cystocytes during coagulation partially explains the previous confusion in distinguishing these two cell types.Evidence is presented which indicates that the plasmatocytes, granular cells and spherule cells represent a developmental series originating from the prohemocytes. Where exactly the cystocytes are derived from is unknown.

Notes: A cardiaca-allatal commissural plexus (CACP) lies between and partly overlapping the postcommissural lobes of the corpora cardiaca (CC), the nervi corpori allati I (NCA I) and the corpora allata (CA). CACP, which is often continuous posteriorly with a complicated postallatal plexus (PAP), comprises a variable number of connectives with neurosecretory processes linking the cardiaca-commissural organ or dorsal cardiac commissure (containig tritocerebral fibres) to the NCA I. the allatal commissure and the CA. Neurosecretory processes are exchanged between the two halves of the cephalic neuroendocrine complex (CNC) both intracerebrally at different locales, possibly to ensure functional synchrony of CNC components.NCA I and CACP are drawn out with their stroma to varying extents over the CA. Histophysiological evidence suggests that part of the stainable secretion stored in, and or in axonal transit through CA may be released through CA surface; NCA I, the nervi cardiostomatogastrici, CACP, perhaps also NCA II may function as neurohaemal areas. A “directed” neurosecretory pathway could be distinguished from PAP to the foregut and the fat body. The degree of spatial intimacy detected between neurosecretory and stomatogastric components of CNC suggests that the two systems may function in an integrated fashion. The recurrent-oesophageal nerve complex serves not only for a direct transport of neurosecretion, but also as one of the sites of its release.

Notes: Relationships between the cribriform plate of the ethmoid, the olfactory bulb, and olfactory acuity were explored using material from 13 of the 17 bat families.All megachiropteran cribriform plates were entirely perforated. In contrast, microchiropteran plates showed distinct perforated portions dorsally and nonperforated portions ventrally. The plates of frugivorous species had more foramina than those of insectivorous ones. Bats with mixed dietary habits were intermediate. Our data suggest that the Chilonycterinae were originally frugivorous, and have only secondarily reverted to an insectivorous diet.Trend analyses show that wherever dietary preference appears to favor a more acute sense of smell, bulb diameter tends to be larger. In general, frugivorous bats tend to have bulbs exceeding 2 mm in diameter; insectivorous bats tend to have bulb diameters of 2 mm or less. The number of foramina in the plates and total cribriform plate area tends to increase as a function of bulb area, but the plate area the foramina occupied increases as a function of bulb volume. The ratio of the size of the bulb to the size of the cerebral hemisphere does not predict olfactory acuity in bats.

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 number, location, size, shape and microstructure of the parathyroid glands of Agama agama agama, Hemidactylus brooki angulatus and Pytodactylus hasselquisti hasselquisti was investigated using approximately 250 specimens of each species from the Zaria area of Nigeria.Only parathyroid III was found. Additional patches of tissue in Hemidactylus, though possibly parathyroid IV, are considered to be derived from parathyroid III. It was found that the amount of parathyroid tissue per gram of body weight was similar in the three species used, and that females had more parathyroid tissue than males. The same situation seems possible in other species.The structure of the parathyroid glands could not be related to taxonomic grouping within the Sauria, but the general picture was found to be more similar to that of birds and mammals than to that of amphibians.

Notes: Mast cells were demonstrated in eight species of snakes, using special fixation techniques to prevent solubilization of cytoplasmic granules. Toluidine blue O and azure A were the major stains and observations were made under light microscope including cytophotometric analysis.The mast cells of snakes were shown to be relatively small (7-11 μ in diameter) when compared to mast cells of a lizard (8-15 μ), dog and rat (9-15 μ).Among the various organs examined, mast cells were particularly numerous in the mesentery, tongue, underneath the serosa of the digestive tract and in the heart, between muscle fibers and in the epicardium.Although under the light microscope some snake mast cells seemed to be orthochromatically stained, when analysed by cytophotometry they were demonstrated to be actually metachromatic.Snake mast cells granules were demonstrated to have an amphoteric behavior, since they were stained with both basic (toluidine blue O and azure A) and acid dyes (eosin and ponceau-acid-fuchsin).

Notes: Fine structure of the torus semicircularis of the loach, carp, common eel and rainbow trout was studied by light and elecron microscopy. The torus semicircularis of each species is divided into four layers. The subependymal first layer comprises numerous unmyelinated fibers and their terminals which contain cored vesicles. The second and the third layers are composed of small cell bodies and their dendrites respectively. These layers develop equally in the four species and contain the usual axodendritic synapses. On the other hand, the fourth layer varies in different species. The mediumsized cells in this layer, which are inferred to be of the same origin as the small cells from their configuration and size, show differences in lamination in each species. Compared with the usual axodendritic synapse of the small cells, the medium-sized cells have quite different synaptic patterns, which include inhibitory and electrical as well as the usual excitatory chemical synapses. From these findings, the medium-sized cells are surmized to receive sound of different degrees of intensity from that received by the small cells, which may have an effect on feeding behaviors of the species. In the deepest portion of the torus semicircularis of all species, there are large multipolar cells on which numerous axon terminals synapse in much the same way as they do on the medium-sized cells. These findings suggest that the synaptic patterns in the torus semicircularis may depend not on the receptive cells in each layer but on the various characteristics of the afferent fibers.

Notes: Retinal projections were studied experimentally in the Northern water snake using modifications of the Nauta silver impregnation technique. Contralaterally, the retina projects to nucleus geniculatus lateralis pars dorsalis and pars ventralis, nucleus lentiformis mesencephali and nucleus geniculatus pretectalis. A sparse projection was also observed to nucleus ovalis. An additional afferent thalamic projection to nucleus ventrolateralis was found in two cases. The retina projects ipsilaterally to the dorsolateral portion of nucleus geniculatus lateralis pars dorsalis, and sparsely to nucleus lentiformis mesencephali and nucleus geniculatus pretectalis. Nucleus posterodorsalis receives dense bilateral retinal projections. Contralaterally, the retina also projects to the superficial layers of the tectum (layers 8-13 of Ramón) and to nucleus opticus tegmenti. Armstrong's findings that the retinal projections in Natrix are qualittatively similar to those in lizards were confirmed. However there are marked quantitative differences among the various pathways and their corresponding nuclei. These differences are particularly striking in comparing the visual projections to the dorsal thalamus, the retino-tecto-rotundal and the retino-geniculate systems. The first is reduced in volume and the second is markedly increased in volume in comparison with lizards. These data lend support to the theories of Walls that snakes evolved from fossorial lizards and of Underwood that the eyes of these lizards underwent reduction but not complete degeneration. Qualitatively the retinal projections are conservative among lizards and snakes, but a history of reduction of these pathways in ancestral snakes with a selective increase in the retino-geniculate system as a surface niche was reattained is reflected in the anatomy of this ophidian visual system.

Notes: Abdominal extra-adrenal chromaffin tissue, or paraganglia, was examined at the ultrastructural level to elucidate the innervation of this adrenal medullary homologue. Paraganglia display unmyelinated nerve fibers surrounded by Schwann cell cytoplasm. These nerves are separated from the paraganglion Type I (granule-containing) cells by cytoplasmic projections of paraganglion Type II (satellite) cells. However, serial sections show that the nerves eventually make synaptic contact with the Type I cell. At the axon-chromaffin cell junction, only the outer aspect of the nerve is covered by the satellite cell. The presynaptic endings contain numerous synaptic vesicles, mitochondria and glycogen particles. The vesicles are predominantly of the clear-cored variety, but a few possess centers which are elecron opaque. The pre- and postsynaptic membranes are separated bya subsynaptic space and occasionally exhibit the membranal densities usually associated with synaptic areas. These ultrastructural studies establish definite evidence that abdominal paraganglion cells are innervated.

Notes: The gland cells of Lyonet's gland, which is accessory to the silk gland in the silkworm larva, is characterized by the presence of complicated canaliculi bearing microvilli on their inner surface, large numbers of mitochondria and remarkably convoluted basal plasma membrane. On the other hand, the cell lacks the well-developed cytoplasmic membrane system such as rough- and smooth-surfaced endoplasmic reticula and Golgi bodies, though free ribosomes are numerous. Secretory vesicles are absent, and the canaliculi contain no dense material. From such ultrastructural observations, it was suggested that a possible role of the gland may be the exchange of the small molecules such as water and ions, rather than the hitherto supposed secretory role of a cementing sunstance of silk proteins. The lumen of the proximal part of the glandular duct contains a kind of proteinaceous substance which can be demonstrated histochemically and is regarded as similar to one of the silk proteins in the silk gland, not to the real product of the Lyonet's gland.