Showing papers in "Journal of Morphology in 1971"

Reproduction and the mechanism of meiotic restitution in the parthenogenetic lizard Cnemidophorus uniparens.

Abstract: Gross details of the reproductive cycle and the cytology of oogenesis were studied in 155 egg clutches produced by 69 captive individuals of the triploid parthenogenetic lizard Cnemidophorus uniparens. The mean clutch cycle lasted 23 days. The mean number of ova per clutch was 3.3, and the mean number of oocytes per right and left ovaries was 1.65 and 1.70, respectively. Comparison of the size of the oocytes at ovulation (9–10 mm) with the estimated mean duration of vitellogenesis (8.8 days) gave an average of approximately 1 mm yolk deposition per day. The mean time for the retention of eggs in the oviducts was 9.3 days. The germinal disc of the oocyte consists of a series of layers formed by the arrangement of various cytoplasmic and yolk particles in the polar region. In a mature oocyte the germinal vesicle is located immediately below the vitelline membrane and lies at the center of the germinal disc. The germinal vesicle is characterized by a dense disc-like cluster of diplotene chromosomes. Diplonema extends until near ovulation when the oocytes have attained a size of about 9 mm. Diakinesis and metaphase I occur rapidly and immediately prior to ovulation. Counts of approximately as many bivalents as there are somatic chromosomes were obtained from oocytes at diakinesis and metaphase I. The second division occurs almost immediately before or at the precise moment of ovulation. The chromosomes of the first polar body consist of dyads, of which there are as many as the triploid number of 69. A metaphase II plate obtained in polar view also revealed dyad chromosomes, of which there were approximately as many as the triploid somatic number. The second telophase is normal as evidenced by formation of the second polar body. Chromosomes from the opposing telophase plates show a monad structure. The presence of as many bivalents in the first division as the triploid somatic number of 69 indicates that the 3N condition of C. uniparens was doubled prior to meiosis. This is further supported by the occurrence of two maturation divisions each giving rise to a polar body, by the dyad structure of the chromosomes in the first polar body and the second metaphase, and by the presence of monochromosomes at telophase II. Thus, parthenogenesis in these lizards is of the meiotic type. The somatic number of chromosomes is doubled early in oogenesis presumably by a premeiotic endoduplication, and the 3N level is restored by two subsequent maturation divisions.

The migration of blood cells of the bone marrow through the sinusoidal wall.

Abstract: Electron microscopic observations on the mechanically undisturbed guinea pig bone marrow show that the sinusoidal lining is continuous. There are neither intercellular nor intracellular apertures allowing free communication between the extravascular and intravascular compartments. A transient migration pore is only formed during the diapedetic transit of blood cells. Serial sections show that this aperture is transcellular. A functional continuity of the sinusoidal lining appears to be maintained during the diapedesis of blood cells, which is evident from the absence of a significant extravascular leakage of plasma during this process.

Attachment and metamorphosis of the cheilo-ctenostome bryozoan bugula neritina (linné).

Abstract: The structure, attachment and subsequent metamorphosis of larvae of the marine bryozoan Bugula neritina were studied by light and electron microscopy. Two points of larval anatomy are of special significance to proper interpretation of the metamorphosis: 1 Two cytologically similar blastemal tissues, each laden with free ribosomes, occur as parts of the apical organ complex. The upper blastema directly contacts the larval surface, forming the non-ciliated rows of the apical organ. The lower blastema is internal and is oral to and contiguous with the upper blastema. 2 The epidermal tissues of the larva are joined in the following sequence, beginning at the aboral pole: a. apical organ complex; b. apical-connecting cell; c. infolded pallial sinus epithelium; d. vesicular-connecting cell; e. aboral vesicular epithelium; f. corona; g. oral vesicular epithelium; and i., j., and k. internal sac neck, wall and roof regions. The initial stages of metamorphosis involve a complex sequence of morphogenetic movements, including: 1 eversion of the internal sac, permanently attaching the larva to the substrate; 2 inrolling of the aboral vesicular epithelium, corona, oral vesicular and ciliated epithelia, and neck region of the internal sac into the larval interior; concomitantly the pallial sinus epithelium evaginates; 3 loss of connection between the invaginated tissues and the surface; 4 fusion of the pallial sinus epithelium with the wall region of the internal sac, maintaining the integrity of the body surface; 5 retraction of the apical organ complex and invagination of the pallial sinus epithelium with the simultaneous elevation of the internal sac wall region to the aboral pole. At the conclusion of these events the preancestrular surface is covered by the wall and roof regions of the internal sac. Cells of the wall region form the epidermis of the body wall except for the attachment disc and secrete a cuticular exoskeleton that is secondarily calcified; the attachment disc is formed by the roof region of the internal sac. Internally, the ectodermal upper blastema differentiates into the lophophore and digestive tract of the ancestrular polypide, while the lower blastema forms the lining of the lophophoral coelom and the splanchnic (but not the somatic) lining of the visceral coelom. The visceral somatic peritoneum is formed from cells that may originate from the mesodermally derived pigmented cells of the larva to which they are similar in pigmentation and cytology. Such a composite derivation of a coelomic lining has not been described previously.

A gross study of the compartmentalized stomach of two new‐world camelids, the llama and guanaco

Abstract: The llama and guanaco stomach consisted of three compartments. A transverse pillar divided the large, first compartment into cranial and caudal sacs. Both sacs contained recessed glandular saccules. The saccules in the caudal sac were everted during the gastric contraction cycle. The non-recessed surfaces of this compartment were covered by stratified squamous epithelium. The first compartment communicated on the right with a smaller, reniform second compartment. Except on the lesser curvature, this compartment contained deep cells which were lined by a papillated glandular mucosa. The ventricular groove, defined by a single muscular lip, coursed along the cranial sac of the first compartment, over the lesser curvature of the second compartment, and terminated at the tubular passage to the third compartment. The initial four-fifths of the elongate third compartment contained mucigenous glands like those found in the saccules and cells of the first and second compartment Proper gastric glands and pyloric glands were confined to the terminal one-fifth of the third compartment. Attempts to homologize the compartments of the camelid stomach with those of the Pecora or so-called advanced ruminants were unsuccessful. The results of this study and concurrent physiologic investigations indicated that the processes of ruminant digestion can operate within wide anatomic boundaries, and that the camelid stomach with its extensive glandular mucosa is adapted for greater digestive efficiency than the advanced ruminant stomach.

Fine structure of the noctuid moth ear. I. The transducer area and connections to the tympanic membrane in Feltia subgothica haworth

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

A structural and functional analysis of walking in the turtle, Chrysemys picta marginata

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

The innervation of the salivary gland in the american cockroach: Light and electron microscopic observations.

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

Growth of the calcareous skeleton during regeneration of spines of the sea urchin, strongylocentrotus purpuratus (stimpson): A light and scanning electron microscopic study.

Abstract: Growth of the skeleton of regenerating spines of the sea urchin, Strongylocentrotus purpuratus, was studied with the light and scanning electron microscopes during the formation of a growth ring or cycle. Growth was initiated about three days after fracture and was linear between 5 and about 40 days after fracture, with a mean rate of 0.16 mm/day. There-after, a decline in growth rate was observed, being attributed to abrasion. The new skeleton first appeared as minute, conical "micro-spines" on the fractured surface of the spine shaft initiating regeneration of the inner zone of meshwork. Subsequent growth of micro-spines of both the developing inner zone of meshwork, and an outer zone of radiating wedges, formed a conical fenestrated skeleton on the fractured surface of the shaft. Further deposition of micro-spines along the shaft, initially at the level of fracture, formed meshwork which gradually became solidified externally resulting in a new cycle about 60 days after fracture. In contrast, a new cycle was initiated at the milled ring in non-fractured spines during total regeneration on bare tubercles, demonstrating that growth of spines also takes place in the absence of fracture. Experiments conducted in vitro demonstrate that spine regeneration is not a polar phenomenon.

The fine structure of the hepatopancreas of the woodlouse, Oniscus ascellus

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

Comparative cardiac anatomy of the reptilia. I. The chambers and septa of the varanid ventricle.

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

Tooth replacement in the red-backed salamander, Plethodon cinereus.

Abstract: The developmental cycle of the teeth in Plethodon cinereus is analyzed on morphological grounds using alizarin preparations. All the stages in development do not occupy the same proportion of the life cycle time. Functional teeth and germs at an early stage in development occupy a large proportion of the life cycle time, whereas the processes of tooth shedding and ankylosis occur very quickly. The time during which any locus does not bear a functional tooth, and is therefore a non-functional locus, is reduced to a minimum. P. cinereus has a basic pattern of tooth replacement which is consistent with Zahnreihen which are 2.0 tooth spaces apart. Variations in the replacement pattern are common and these are produced by relatively small fluctuations in the spacing of the Zahnreihen around the „mean„ of 2.0. Localized disturbances which produce breaks in the replacement pattern and cause waves to cross also occur. These may be due to the failure of tooth germs to develop, the fusion of tooth germs, or may be the result of the inherent variability in a complex biological system. This variability causes individual tooth germs to develop too slowly or too quickly and hence assume an „abnormal” position thus causing breaks in the replacement pattern. Tooth replacement may be controlled by an intra-local mechanism(s) rather than by stimuli which travel along the jaw.

Fine structure of the antenna and its sensory cone in larvae of Aedes aegypti (L.)

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

Spermatogenesis in bombyx mori. I. The canal system joining sister spermatocytes.

Abstract: An electron microscopic investigation was made of the origin and morphology of the canal system that connects sister spermatocytes of larval Bombyx mori. Canal formation results from incomplete cleavages during the mitoses which immediately precede meiosis. We suggest the lip which surrounds each canal is derived from the contractile ring which is prevented from constricting completely by interaction with the midbody. Cells were found with as many as four canals which demonstrates that canal rims can persist through a number of mitotic cycles. Speculations are advanced as to the significance of these canals in restricting gonocytes from unlimited divisions.

Light microscopic studies on the pineal organ in teleost fishes with special regard to its function

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

The number of centrioles in insect sperm: a study in two kinds of differentiating silkworm spermatids.

Abstract: The typical eupyrene and atypical apyrene cycles of sperm differentiation in Bombyx mori were studied, with special attention to centriole number and behavior. Contrary to other reports, there is always only one centriole in the differentiating and in the mature sperm, thus confirming our previous findings that insect sperm has one centriole at the base of the flagellum, in contrast to two centrioles found in many other groups of animals. This numerical difference is discussed in an evolutionary context.

Fine structure of the chemoreceptor sensillum in Limulus

Abstract: Each chemoreceptor sensillum of Limulus polyphemus consists of 6–15 bipolar neurosensory cells with distal processes confined within a single cuticular tubule as they extend to the outside environment. The cuticular tubule, which is enveloped by the cuticulo-tubal cell, opens proximally into a fluid-filled extracellular space through which the dendrite passes before entering the cuticular tubule. Between the neurosensory cells are one to three microvillar cells also exposed to the extracellular space. This space is enclosed by a sheath cell extending proximally from the inner opening of the cuticular tubule and enveloping the proximal portions of the dendrites, the distal portions of the microvillar cells, as well as the distal portion of some neurosensory cell bodies. Most of the remaining portions of the neurosensory cells and microvillar cells are enveloped by neuroglia. Tight junctions occur between the distal portions of the dendrites in or near the cuticular tubule. Each dendrite has a cilium-like segment located where it traverses the extracellular space with a 9 + 0 pattern of fibers. Septuplelayered junctions occur among the proximal portions of some dendrites and some neurosensory cell bodies of the same sensillum. The subjacent processes of the sensillum frequently course proximally as isolated axons before joining nerve bundles. In the chilarial and gnathobasal chemoreceptors these nerve bundles course proximally to neuropile clumps of a peripheral nerve plexus. The presence of numerous synaptic vesicles in the neuropiles suggests that chemical transmission may occur among “en passant” synapses formed by the axons. Proximally the neuropiles are joined to the central nervous system by relatively long nerves.

The light and the electron microscopic studies of Peyer's patches in non germ-free adult mice.

Abstract: Peyer's patches of conventional adult mice are studied with light and electron microscopy. Based on cellular types and distribution, each lymphoid follicle of Peyer's patch is divisible into four zones: the germinal center, the small lymphocytic, the interfollicular and the subepithelial zones. Three distinct cell types are present in the germinal center, i.e., dendritic reticular cells; tingible body macrophages; and lymphocytes which are classifiable into large, medium and small size. The medium size lymphocytes are the great majority in this zone. The small lymphocytic zones are characterized by a predominance of small lymphocytes with a few reticular cells. The subepithelial zone has a remarkable accumulation of macrophages and plasma cells. In the interfollicular zones there are predominantly small lymphocytes with considerable round macrophages and plasma cells, and this zone is permeated with several post-capillary venules. The distinctive characteristics of small capillaries of the patches are also described.

The ontogenic development of the vertebrae in some Gekkonoid lizards

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

Some developmental aspects of the head skeleton of the 35–37 mm Squalus acanthias foetus

Abstract: Two specimens of a group of five foetuses, 35–37 mm in total length, of Squalus acanthias were serially sectioned and stained. These specimens were studied for the purpose of testing statements made in the literature, especially by Holmgren ('40), regarding cell sources and skeletal development. Many of Holmgren's results were confirmed with some important differences in detail. Limited blastemas of dermal bones were not evident although a diffuse subepidermal blastema was present in certain areas. There is evidence of delamination addition to the jaws and many parts of the endocranium. Although the trabecula is in part of visceral origin, the visceral material does not represent an infrapharyngohyal since it always has been an integral part of the endocranium, never a formed element of the arch. The same applies to the pharyngo region of the hyoid arch. The pharyngohyal tissue forms the area of articulation of the hyomandibula and the lamina hypotica. Thus a typical lateral commissure is not formed and the resulting otic capsule-basicranial association is unique to the elasmobranchs. The hyomandibula is the epihyal and there is no evidence of a symplectic in this group. The jaws appear to incorporate delamination tissue, associated in teleostomes with dermal bone, in addition to the neural crest proper.

Structural and physiological changes associated with the growth of avian fast and slow muscle.

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

Organogenesis in normal and lobeless embryos of the marine prosobranch gastropod Ilyanassa obsoleta

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

The histology of the first batch of eggs and their associated tissues in the ovariole of Dysdercus fasciatus signoret (heteroptera: Pyrrhocoridae) as seen with the light microscope.

Abstract: In the telotrophic ovarioles of Dysdercus fasciatus, mononucleate, binucleate and multinucleate trophocytes are seen in the germarium Cellular breakdown of the multinucleate cells is seen in the posterior part of this tissue The nutritive cords, which are continuous with the trophic core at the one end and the oocytes of the vitellarium at the other, contain material of fibrous appearance which continues into the trophic core The ovariole is enclosed in two sheaths throughout its length Prefollicular tissue in the germarium appears to give rise to the follicle cells Mitosis is common in this zone Oocytes are at first surrounded by a multilayered epithelium This is later reduced progressively to one layer This one layered follicular epithelium is at first columnar but then changes to cuboidal mononucleate, cuboidal binucleate and finally to a squamous binucleate condition This epithelium thus seems to accommodate the increased volume of the oocyte by growth and a change of shape The oocyte grows fastest at those times when it is surrounded by cuboidal and squamous epithelial cells

Ontogeny of cranial ossification in the small-mouthed salamander, Ambystoma texanum (Matthes)†

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

Striated visceral muscle of drosophila melanogaster.

Abstract: Striated visceral muscle cells are scattered singly or in small groups at the base of the intestinal cells of the mid-gut of Drosophila melanogaster larvae. Fibers less than 1 μ in diameter, designated as small, contain a single myofibril, few, if any, dyads and few mitochondria. Fibers of somewhat larger diameter contain dyads and more mitochondria. Both types of fiber have a perforate Z band which appears as discontinuous bodies in longitudinal sections and as a perforate sheet of dense rims and clear perforations in transverse sections. The Z rims contain filaments, 30 to 50 A, oriented in the transverse direction. The number and arrangement of myofilaments and the ultrastructure of the Z band are consistent with the function of these muscles.

The fine structure of the pigment epithelium and photoreceptor cells of the newt, Triturus viridescens dorsalis (Rafinesque)†

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

A fine structural analysis of the epidermis and cuticle of the oligochaete aeolosoma Bengalense stephenson.

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

Spermatogenesis in Bombyx mori. II. The ultrastructure of synapsed bivalents

Abstract: In Bombyx mori the male is the homogametic sex, crossing over occurs only in males, and chiasmata are observed in spermatocytes, but not in oocyte nuclei. If the assembly of synaptonemal complexes is an essential prerequisite for genetic crossing over and chiasmata formation, then the nuclei of Bombyx spermatocytes should contain synaptonemal complexes. Synaptonemal complexes were found in spermatocytes from young four instar larvae. The structure of meiotic bivalents is described using micrographs taken with 100 and 1000 KV electron microscopes. These data together with that from the literature are used to construct a three-dimensional model of the synaptonemal complex and to suggest its method of origin and its function during crossing over.

Antennal sense organs of the cockroach, Leucophaea maderae.

Abstract: Adult and nymphal antennae of the cockroach, Leucophaea maderae, contain nine or more different morphological types of sense organs. There is no outwardly apparent sexual dimorphism in adult antennae. Nymphs are dificient in gross numbers of sensilla. Sense organs are classified morphologically by their similarity to known types of sensila and are assigned functions on this basis and preliminary electrophysiological data: Sensilla chaetica (A), thick-walled mechanoreceptive hairs in groups on the antennal base; S. chaetica (B), thick-walled setae which are tactile and probably chemoreceptive, occurring in the antennal base and flagellum; S. trichodea (A), thin-walled chemoreceptive hairs of the flagellum; S. trichodea (B), minute hairs on the scape and pedicel; S. basiconica, thin-walled chemoreceptive pegs, and S. coeloconica („pit-pegs”) of the flagellum; S. campaniformia and scolopidia, mechanoreceptors in the base and flagellum; plus Johnston's organ and/or connective chrodotonal organs in the pedicel. Calculations based on absolute counts of sensilla and their known innervation yield an estimate of about 3.3 × 104 sensilla and 105 cells per antenna.

Fine structure of the carp torus longitudinalis

Abstract: Fine structure of the carp torus longitudinalis was studied by electron and light microscopy and compared with the granular layer of the carp cerebellum. There are three types of cells in the torus longitudinalis, that is, small, medium-sized and large cells. From the small cells to the medium-sized cells, there is gradual transition in size and in the amounts of cell organelles. These cell profiles and the closely packed cell pattern in a part of the torus longitudinalis are quite similar to those in the granular layer of the cerebellum. Moreover, peculiar synaptic configurations of so-called “synaptic glomeruli” are found both in the torus longitudinalis and in the granular layer of the cerebellum. In the torus longitudinalis, unmyelinated nerve fibers are seen to have bulbous swellings along their course, most of which contain a mitochondrion, as do they in the carp tectum opticum. It is speculated that the torus longitudinalis may be partly related to the granular layer of the cerebellum and partly to the tectum opticum.

Tensile forces in skeletal structures.

Abstract: Recent hypotheses about the mechanisms of adaptation of bone to impressed mechanical forces differ according to the extent to which tensile stresses are thought to be functionally important in bone. A pilot study of three anatomical regions by means of the photoelastic analogy suggests the possibility that net tension rarely exists in significantly large regions of bones during normal function. Thus the examination of two situations (opposite linear attachment of muscles to the lips of bony crests and opposite areal attachment of muscles to either side of thin bony plates) suggests that in rare cases where precise anatomical architecture is such that net tension may be present, then bone is not found; such regions consist of appropriate collagenous structures. In the third situation (opposite attachment of tendons to a sesamoid bone) where it would appear that net tension ought to exist, it is suggested that it is likely that it does not. Net tension probably occurs only in tendons running in tightly curved bony grooves: those very situations where sesamoid bones are not present.