Showing papers in "Journal of Morphology in 1979"

The Functional Significance of Primate Mandibular Form

Abstract: A stress analysis of the primate mandible suggests that vertically deep jaws in the molar region are usually an adaptation to counter increased sagittal bending stress about the balancing-side mandibular corpus during unilateral mastication. This increased bending stress about the balancing side is caused by an increase in the amount of balancing-side muscle force. Furthermore, this increased muscle force will also cause an increase in dorso-ventral shear stress along the mandibular symphysis. Since increased symphyseal stress can be countered by symphyseal fusion and as increased bending stress can be countered by a deeper jaw, deep jaws and symphyseal fusion are often part of the same functional pattern. In some primates (e.g., Cercocebus albigena), deep jaws are an adaptation to counter bending in the sagittal plane during powerful incisor biting, rather than during unilateral mastication. The stress analysis of the primate mandible also suggests that jaws which are transversely thick in the molar region are an adaptation to counter increased torsion about the long axis of the working-side mandibular corpus during unilateral mastication. Increased torsion of the mandibular corpus can be caused by an increase in masticatory muscle force, an increase in the transverse component of the postcanine bite force and/or an increase in premolar use during mastication. Patterns of masticatory muscle force were estimated for galagos and macaques, demonstrating that the ratio of working-side muscle force to balancing-side muscle force is approximately 1.5:1 in macaques and 3.5:1 in galagos during unilateral isometric molar biting. These data support the hypothesis that mandibular symphyseal fusion is an adaptative response to maximize unilateral molar bite force by utilizing a greater percentage of balancing-side muscle force.

Mandibular function in Galago crassicaudatus and Macaca fascicularis: an in vivo approach to stress analysis of the mandible.

Abstract: Single-element and/or rosette strain gages were bonded to mandibular cortical bone in Galago crassicaudatus and Macaca fascicularis. Five galago and eleven macaque bone strain experiments were performed and analyzed. In vivo bone strain was recorded from the lateral surface of the mandibular corpus below the postcanine tooth row during transducer biting and during mastication and ingestion of food objects. In macaques and galagos, the mandibular corpus on the balancing side is primarily bent in the sagittal plane during mastication and is both twisted about its long axis and bent in the sagittal plane during transducer biting. On the working side, it is primarily twisted about its long axis and directly sheared perpendicular to its long axis, and portions of it are bent in the sagittal plane during mastication and molar transducer biting. In macaques, the mandibular corpus on each side is primarily bent in the sagittal plane and twisted during incisal transducer biting and ingestion of food objects, and it is transversely bent and slightly twisted during jaw opening. Since galagos usually refused to bite the transducer or food objects with their incisors, an adequate characterization of mandibular stress patterns during these behaviors was not possible. In galagos the mandibular corpus experiences very little transverse bending stress during jaw opening, perhaps in part due to its unfused mandibular symphysis. Marked differences in the patterns of mandibular bone strain were present between galagos and macaques during the masticatory power stroke and during transducer biting. Galagos consistently had much more strain on the working side of the mandibular corpus than on the balancing side. These experiments support the hypothesis that galagos, in contrast to macaques, employ a larger amount of working-side muscle force relative to the balancing-side muscle force during unilateral biting and mastication, and that the fused mandibular symphysis is an adaption to use a maximal amount of balancing-side muscle force during unilateral biting and mastication. These experiments also demonstrate the effects that rosette position, bite force magnitudes, and types of food eaten have on recorded mandibular strain patterns.

Temperature levels and periods of sex determination during incubation of eggs of Chelydra serpentina.

Abstract: Eggs of Chelydra serpentina were shifted during incubation between the female producing temperatures of 20°C or 30°C and the male producing temperature of 26°C. In the 20°C and 26°C combination, the stages during which incubation temperature determined sex were stage 14 through stage 16 (stages of normal series, Yntema, '68). In the 30°C and 26°C combination, the temperature sensitive stages for sex determination were stage 14 through stage 19. Incubation at 26°C throughout this period was needed to produce all males. Incubation at 30°C during either the first or second half of the period produced nearly all females; shorter periods of incubation at 30°C were more effective in producing females during the second half of the sensitive period. In the 20°C and 26°C combination, incubation at 20°C or 26°C for parts of the sensitive period produced both males and females. In three of the 57 clutches of eggs used in the experiments, incidence of females was atypically high.

Keratin formation and barrier mechanisms in the epidermis of Natrix natrix (Reptilia: Serpentes): An ultrastructural study.

Abstract: A β-keratin pattern, consisting of 30 A filaments embedded in an amorphous matrix, is formed by fusion of membrane-bound packets with the 70 A filaments of immature cells. This pattern occurs in the Oberhautchen and the β-layer. When completely mature, these two components show no cell boundaries. It is suggested that this feature is associated with the process that leads to the separation of outer and inner epidermal generation. Filaments of 100-150 A embedded in an amorphous matrix form the α-keratin pattern, which occurs in the α-layer only. The lacunar tissue is regarded as consisting of cells resembling immature α-cells, whereas mesos and clear layer show a keratin-like material consisting of 100-150 A filaments without matrix. This is regarded as a modification of α-keratin. The cells of all components synthesizing α-keratin (α, mesos and clear layer) have the following features in common: (1) the plasma membrane is modified in that its inner leaflet is obscured by the deposition of a marginal layer, and (2) the cells have 0.06-0.1 μm mucous granules containing mucopolysaccharides, which release their content into the intercellular space. Protective and barrier functions of the epidermis are provided by the following features: (1) Oberhautchen and β-layer merge during final maturation to a homogenous stratum of β-keratin without intercellular spaces. Their function seems to be mechanical protection. (2) The marginal layer of α-keratin containing cells, which decreases in thickness from without inwards, is highly resistant to physical and chemical influences. (3) Mesos granules contain phos-pholipid-lamellae, which are partly discharged into the intercellular space and partly remain within the mesos cells. These lipid lamellae are believed to contribute to the establishment of the permeability barrier. (4) The content of mucous granules may play a role in immunological processes. (5) Tight junctions seal off the intercellular space between the uppermost living cells of the epidermis and contribute to the permeability barrier.

Functional significance of the mandibular symphysis.

Abstract: The purpose of this investigation was to relate the morphology of connective tissues in the mandibular symphysis to the behavioral and experimental evidence for mobility and mechanical stress at the symphysis. The anatomy of the symphysis was examined histologically in 6 mammalian orders encompassing 22 species. Behavioral and experimental evidence of stress during the power stroke of the chewing cycle correspond with stresses at the symphysis implied by the location and orientation of symphyseal connective tissues. These stresses are: (1) dorsoventral shear of the symphysis due to the transfer of force from balancing to chewing sides, (2) bending of the symphysis causing tension along the inferior and compression along superior borders due to torsion on the dentaries from the jaw closing muscles, and (3) antero-posterior shear of the symphysis due to an anteriorly directed stress on the chewing side. Interspecific comparisons suggest that leaf eaters can resist greater dorsoventral shear than fruit or insect eaters, but no correlations exist between diet and bending or antero-posterior shear. This suggests that chewing leaves requires larger biting forces.

A comparative study of the differentiation and involution of the Mullerian duct and Wolffian duct in the male and female fetal mouse.

Abstract: The present investigation has examined the ultrastructural differentiation of the genital ducts of both sexes of fetal mice. The emphasis of observations was placed on the phenomenon of morphogenetic cytolysis, particularly during the critical periods of Wolffian duct stabilization and Mullerian duct involution. Both developing and regressing genital ducts evidence extensive cytolysis. Autophagy appears to be the mechanism of morphogenetic change in the developing male Wolffian duct. Autophagy, heterophagy, and degeneration in situ are all prominent cytolytic activities in female Wolffian duct involution. The developing female Mullerian duct undergoes extensive morphogenetic remodeling by the mechanisms of autophagy, heterophagy, and degeneration in situ. In the male Mullerian duct, autophagy, heterophagy, and degeneration in situ are also prominent. In addition, whole degenerated epithelial cells are extruded from the duct early in regression which may be related to the transformation of periductal mesenchymal cells into an “epithelioid cell cuff” which does not form around the regressing Wolffian duct. The formation of this mesenchymal condensation surrounding the duct is also accompanied by the protrusion of Mullerian epithelial cell cytoplasm into the mesenchymal cells. These observations may evidence a complex epithelial-mesenchymal interaction occurring during male Mullerian duct involution.

Fine structural studies of the nervous system and the apical organ in the planula larva of the sea anemone Anthopleura elegantissima.

Abstract: The nervous system of the planula larva of Anthopleura elegantissima consists of an apical organ, one type of endodermal receptor cell, two types of ectodermal receptor cells, central neurons and nerve plexus. Both interneural and neuromuscular synapses are found in the nerve plexus. The apical organ is a collection of about 100 long, columnar cells each bearing a long cilium and a collar of about 10 microvilli. The cilia of the apical organ are twisted together to form an apical tuft. The ciliary rootlets of the apical organ cells are extremely long, reaching to the basal processes of the cells adjacent to the mesoglea. All three types of sensory cells are tall and slender in profile and are identified by the presence of one or more of the following features: microtubules, small vesicles, membrane-bound granules and synapses. The interneurons are bipolar cells with somas restricted to the aboral end, adjacent to the apical organ. All synapses observed are polarized or asymmetrical. A diagram including all the elements of the nervous system is presented and the possible functions of the nervous system are discussed in relation to larval behavior.

Comparative cardiac anatomy of the reptilia. III. The heart of crocodilians and an hypothesis on the completion of the interventricular septum of crocodilians and birds.

Abstract: The heart of Crocodylus porosus is described, and deemed to be typical of living crocodilians after examination of the hearts of Alligator mississippiensis, Caiman crocodilus ssp., Crocodylus johnstoni and Crocodylus n. novaeguineae. Some inconsistencies between the anatomy and supposed patterns of blood flow are discussed. The crocodilian heart is compared with, and seen as an advancement of, the heart of non-crocodilian reptiles. The varanid ventricle is re-examined, as it appeared to contain many crocodilian features, along with the ophidian characteristics described previously. The broad similarities within the three groups are interpreted as adaptations towards a high pressure systemic circulation. Consequently varanids and snakes show the same left and right ventricles, as do crocodilians and birds. The evolution of the complete interventricular septum of crocodilians and birds appears to have involved three major trends: firstly, the development of a high pressure left ventricle and the fusion of most of the combined atrio-ventricular valve to the ostium of the right systemic artery; secondly, a line in which right to left shunting became gradually redundant and the vertical septum was completed to the aortico-pulmonary septum (giving rise to the avian ventricle); and thirdly, a line in which right to left shunting became increasingly important, and the vertical septum completed to the interaortic septum (giving rise to the crocodilian ventricle). Perhaps the crocodilian ancestry included a crocodile that was far more aquatic than any extant species.

Ultrastructure of Calcified Cartilage in the Endoskeletal Tesserae of Sharks

Abstract: The tesserate pattern of endoskeletal calcification has been investigated in jaws, gill arches, vertebral arches and fins of the sharks Carcharhinus menisorrah, Triaenodon obesus and Negaprion brevirostris by techniques of light and electron microscopy. Individual tesserae develop peripherally at the boundary between cartilage and perichondrium. An inner zone, the body, is composed of calcified cartilage containing viable chondrocytes separated by basophilic contour lines which have been called Liesegang waves or rings. The outer zone of tesserae, the cap, is composed of calcified tissue which appears to be produced by perichondrial fibroblasts more directly, i.e., without first differentiating as chondroblasts. Furthermore, the cap zone is penetrated by acidophilic Sharpey fibers of collagen. It is suggested that scleroblasts of the cap zone could be classified as osteoblasts. If so, the cap could be considered a thin veneer of bone atop the calcified cartilage of the body of a tessera. By scanning electron microscopy it was observed that outer and inner surfaces of tesserae differ in appearance. Calcospherites and hydroxyapatite crystals similar to those commonly seen on the surface of bone are present on the outer surface of the tessera adjacent to the perichondrium. On the inner surface adjoining hyaline cartilage, however, calcospherites of variable size are the predominant surface feature. Transmission electron microscopy shows calcification in close association with coarse collagen fibrils on the outer side of a tessera, but such fibrils are absent from the cartilaginous matrix along the under side of tesserae. Calcified cartilage as a tissue type in the endoskeleton of sharks is a primitive vertebrate characteristic. Calcification in the tesserate pattern occurring in modern Chondrichthyes may be derived from an ancestral pattern of a continuous bed of calcified cartilage underlying a layer of perichondral bone, as theorized by Orvig (1951); or the tesserate pattern in these fish may itself be primitive.

The morphogenesis of the thigh of the mouse with special reference to tetrapod muscle homologies.

Abstract: In order to provide an ontogenetic basis for the establishment of tetrapod muscle homologies and for the analysis of complex mammalian muscle states, a descriptive analysis of the morphogenesis of the thigh of Mus musculus has been made. The pattern and sequence of muscle cleavage and the migrations of individual muscle primordia are characterized from the eleventh day of gestation, when cleavage begins, through early neonatal stages. Observations on skeletal differentiation and lumbosacral plexus formation are also included. Thigh muscle morphogenesis is compared to that in the lizard, Lacerta, (Romer, '42) and the chick (Romer, '27) and homologies identified. An onogenetic basis for the definition of ancestral and derived muscle states is provided in muscles that are morphologically variable in mammals. These include the gluteus minimus, gracilis, adductor brevis and several hamstring muscles. Certain muscles that show variable innervation patterns in adult mammals, i.e., pectineus, quadratus and adductor magnus, typically develop from premuscle regions that separate muscle anlagen innervated by different nerves. Two muscle anlagen appear in the embryonic mouse thigh and then disappear late in prenatal or early postnatal development. Comparisons with other mammals, especially the marsupial, Marmosa, reveal that these muscles are phylogenetic vestiges that degenerate before maturity. A sartorius vestige is identifiable through the thirteenth day of gestation. A tenuissimus anlage is present until shortly after birth and is clearly innervated by a branch of the peroneal nerve.

The hind limb musculature of the brown kiwi, Apteryx australis mantelli

Abstract: The most complete account of the hind leg muscles of the kiwi was published a century ago by Sir Richard Owen, in his seventy-fifth year. This extensively-cited work has several omissions and errors, and while certain of these were corrected by subsequent authors, sufficient uncertainty remains to warrant a reinvestigation. In the present study a detailed description of the hind leg musculature is given, based upon dissections of two frozen specimens. An indication of the possible function of each muscle is given by assessing its size, action, and fiber-arrangement, together with tentative data on the relative abundance of twitch and tonus fibers. The correlation between surface features of bones and muscle attachments is investigated with a view to interpreting palaeontological material. Although the limb and pelvic bones are marked by numerous features which suggest muscle attachments, relatively few can be positively identified with specific muscles. Only 23% of the muscle origins and insertions can be identified, and, with three possible exceptions, no indication of relative size is given by the scars. The possibility of being able to reconstruct the musculature of the kiwi from its skeletal anatomy, much less that of its extinct relatives, is remote.

Ultrastructure of the somatic portion of the gonads in asteroids, with emphasis on flagellated-collar cells and nutrient transport.

Abstract: Somatic portions of gonads in two phanerozonian sea-stars, Ctenodiscus crispatus and Hippasteria phrygiana, were similar in all aspects of gross structure and histology seen previously in both forcipulate and spinulosan asteroids. For the first time, detailed ultrastructural observations have been made of cells and tissues that reveal several features believed to be of universal occurrence in the gonads of asteroids. These include flagellated-collar cells in the visceral peritoneum and other coelomically derived epithelia, muscular-flagellated-collar cells in the visceral peritoneum and genital coelomic (perihaemal) sinus, the digestion of collagen fibers by cells in the connective tissue layer, and the intimate relationship of the genital haemal sinus and the entire germinal epithelium. Structural and functional compartmentalization are discussed in relation to major activities of the gonad throughout the annual reproductive cycle. The distinctive ultrastructure and current generation of flagellated-collar cells found in the visceral peritoneum are analyzed relative to their role in nutrient transport to gonadal tissues. The single flagellum of each flagellated-collar cell beats in coordination with those on neighboring cells to produce extremely rapid, oriented currents of coelomic fluid. The form of beating in an individual flagellum is planar, and the resulting synchronized activity of many adjacent flagella is non-metachronal; both of these characteristic aspects of current production have, thus far, been encountered together only in the Echinodermata. Flagellated-collar cells are efficient in generating currents which mix contents of the coelomic fluid, and they can presumably supply themselves with nutrients. It is concluded that nutrients so obtained are generally not passed through the wall of the gonad to the germinal epithelium and, as a result, have little to do with nutrition of somatic and germinal cells of the germinal epithelium. Alternatively, well-developed genital portions of the haemal system of the sea-star are advanced as the major channels supplying nutrients to germinal epithelia during gametogenesis.

Structure and carbohydrate histochemistry of the intestine in ten teleostean species.

Abstract: The morphology and carbohydrate histochemistry of ten teleostean intestines are compared. Although there is an absence of regional differentiation seen in higher vertebrates, specializations in some species occur in the form of intestinal swellings, pyloric ceca and recta, the latter separated by a valve. The intestinal lumen is lined by a simple columnar epithelium interspersed with goblet cells; multicellular intestinal glands are absent. Thick basement membranes seen in centrarchids and Perca flavescens closely resemble the stratum compactum found in the lamina propria of esocids. Granular cells, which vary in number from species to species, are often seen in the mucosa and submucosa but less frequently in the muscularis. In species with intestino-rectal valves, a rectum is easily defined by the abrupt appearance of lower mucosal folds, more goblet cells and a thicker muscularis. In the remaining species the above features appear gradually in the distal intestine. Goblet cells show species variations in localization of epithelial mucosubstances, which in broad terms are recognized as sulfomucins, sialomucins and neutral mucosubstances. In both proximal and distal intestines the majority of goblet cells contain sialomucin although small amounts of sulfomucin are also often present. In species without intestino-rectal valves, no changes in carbohydrates occur between proximal and distal intestines. The possible significance of the heterogeneous character of digestive tract mucosubstances is discussed.

Surface anatomy of branchial food traps of tadpoles: A comparative study.

Abstract: Branchial food traps are regions of specialized secretory tissue in the tadpole pharynx, where suspended food particles are trapped in mucus. Light and scanning electron microscopy were used to study branchial food traps from larvae of ten anuran families (36 species). Most anuran larvae from "advanced" (suborder Neobatrachia) families (e.g., Hylidae, Ranidae, Bufonidae) have distinct secretory pits at the posterior margins of the branchial food traps and secretory ridges elsewhere on these surfaces. The apices of columnar PAS-positive, secretory cells are exposed on the floors of the secretory pits or in rows at the tops of the secretory ridges (secretory zone). Tadpoles from most "archaic" (suborder Archaeobatrachia) families (Ascaphidae, Discoglossidae and Pelobatidae) either lack secretory pits, or have them poorly defined. They also lack secretory ridges but have columnar, mucus-secreting cells whose apices are exposed in a seemingly random fashion in the branchial food traps. Rhinophrynus (Archaeobatrachia: Rhinophrynidae) has secretory ridges, but the apices of secretory cells are not arranged in rows at the tops of the ridges; instead they erupt singly or in small clusters on the epithelial surface, in a pattern similar to that in Ascaphus, the discoglossids and the pelobatids. It is proposed that the generalized condition for the branchial food trap mucosa is one where the apices of secretory cells are exposed haphazardly on a flat epithelium and the derived condition is one where the surface is organized into ridges. The morphology of the branchial food traps in Rhinophrynus suggests that, phylogenetically, ridges preceded the coalescing of secretory cell apices into distinct rows. Pipidae and Microhylidae have unique patterns in the gross and microanatomy of their branchial food traps specific to their families. Branchial food trap morphology relates to diets of tadpoles as well as to taxonomy. Obligate macrophagous (e.g., carnivorous) tadpoles, irrespective of family, tend to have reduced branchial food traps, regularly lack secretory ridges and, in extreme cases, lack columnar mucus-secreting cells. Obligate microphagous forms (midwater suspension feeding of Xenopus, microhylids and Agalychnis), have straight parallel secretory ridges with narrow secretory zones and shallow troughs between the ridges. Secretory ridges may help to form mucus strands in which food particles are trapped, but they are not essential for planktonic entrapment. The hydrodynamic implications of the various topographic patterns remain unclear.

Ultrastructure of chloride cells in young adults of the anadromous sea lamprey, Petromyzon marinus L., in fresh water and during adaptation to sea water.

Abstract: The chloride cells in the interlamellar areas of the gills of young adult, anadromous sea lampreys, Petromyzon marinus L., captured in fresh water undergo structural modification during the adaptation of these animals to sea water. In fresh water the chloride cells are partially overlapped by mucus-secreting superficial cells and contain an extensive reticulum of cytoplasmic tubules, which are confluent with both lateral and basal plasma membranes, numerous mitochondria, a Golgi complex of moderate size, and numerous apical vesicles. Adaptation to sea water results in a retraction of the superficial cells, exposing the entire apical surface of the chloride cells, and a proliferation of both cytoplasmic tubules and mitochondria. Extensive enlargement of the Golgi complex in the chloride cells of these animals suggests the involvement of this organelle in the proliferation of cytoplasmic tubules. The extracellular tracer, ruthenium red, enters the tubules from the lateral or basal intercellular spaces in both freshwater- and seawater-adapted animals but never enters either tubules or vesicles from the apical surfaces, indicating that these are not confluent. The presence of dividing basal cells and newly-forming chloride cells, combined with evidence of degeneration of chloride cells, suggests that there is a turnover of this cell type. Both superficial and basal cells are phagocytic and involved in heterophagy of degenerating chloride cells. This phenomenon occurs in both fresh water and sea water indicating that the chloride cells may be functional in both environments.

The timing of the onset of osteogenesis in the tibia of the embryonic chick

Abstract: Haematoxylin, Alcian Blue-Chlorantine Fast Red (ABCR) and the Ralis osteoid-specific stain were employed to closely follow the histogenesis of the tibia of the embryonic chick so as to provide an accurate description of the onset of ossification. An overview of the major cytological events preceding osteogenesis in the tibia was obtained from hindlimbs of embryos of H. H. (Hamburger and Hamilton, '51) stages 16-26 (2.5-5 days of incubation) stained with ABCR. A description of the cytological changes in the periosteum as it develops from the perichondrium and an analysis of the timing of the onset of osteoid deposition was obtained from the tibiae of accurately aged and staged embryos of H. H. stages 28-32 (5.5-8 days). These tibiae were stained specifically for the detection of osteoid:the freshly-secreted, unmineralized product of fully-differentiated osteoblasts. The perichondrium transformed into a bi-layered periosteum at H. H. late stage 29 (6.5 days) while osteoid was first detected adjacent to the hypertrophic cartilage of H. H. stage 30 (6.5-7 days) tibial diaphyses. These results, correlated with the immunoflourescent studies of Von der Mark et al. ('76a,b), which revealed the presence of Type I (bone-type) collagen-synthesizing cells in the perichondria of tibiae from embryos of H. H. stage 28 (5.5-6 days), demonstrated that the onset of determination of cells for osteogenesis and the cytodifferentiation of the periosteum are not temporally coupled.

Leucophores and iridophores of Fundulus heteroclitus: Biophysical and ultrastructural properties.

Abstract: Classical light microscopic studies on pigmentation of Fundulus heteroclitus (killifish) indicated that there are three groups of light reflecting cells; one group on the surface of scales reflects white light, while two other deeper groups (the melaniridophores and the stratum argenteum) are iridescent. The results presented here show that: (1) The scale leucophores reflect white light by a Tyndall light-scattering mechanism, by virtue of the presence of randomly oriented organelles of "novel" morphology. (2) The iridophores of the melaniridophores contain stacks of irregularly-spaced, large reflecting platelets which function as an imperfect multiple thin layer interference system. (3) The stratum argenteum consists of a continuous layer(s) of iridophores with reflecting platelets which are so regularly packed as to approach an ideal multiple thin layer interference system. (4) In all three types of light reflecting cells, the dimensions and packing (orientation) of the reflecting organelles satisfactorily account for the chromogenic properties of the cells, including colors as viewed under transmitted, reflected, or polarized light. (5) The spacial relationships between these light reflecting cells and adjoining melanophores are different for each type of light reflecting cell. Furthermore, we propose to replace the term reflecting platelet with refractosome.

Structure of the shell and tertiary membranes of eggs of softshell turtles (Trionyx spiniferus).

Abstract: Eggs of the turtle Trionyx spiniferus are rigid, calcareous spheres averaging 2.5 cm in diameter. The eggshell is morphologically very similar to avian eggshells. The outer crystalline layer is composed of roughly columnar aggregates, or shell units, of calcium carbonate in the aragonite form. Each shell unit tapers to a somewhat conical tip at its base. Interior to the crystalline layer are two tertiary egg membranes: the outer shell membrane and the inner shell membrane. The outer shell membrane is firmly attached to the inner surface of the shell, and the two membranes are in contact except at the air cell, where the inner shell membrane separates from the outer shell membrane. Both membranes are multi-layered, with the inner shell membrane exhibiting a more fibrous structure than the outer shell membrane. Numerous pores are found in the eggshell, and these generally occur at the intersection of four or more shell units.

Studies on fish scale formation and resorption. I. Fine structure and calcification of the scales in Fundulus heteroclitus (Atheriniformes: Cyprinodontidae).

Abstract: Fine structure of the scales of Fundulus heteroclitus was examined by scanning and transmission electron microscopy. The concentric ridges of the scale surface were characterized by the presence of minute, highly calcified, denticles or tooth-like processes. Needle-shaped crystals of hydrox-yapatite were precipitated not only in the osseous layer but in the intimate lamellae of the fibrillary plate except in portions just below the grooves. The calcification of the osseous layer was observed to proceed by filling the matrix with patches of crystals. The fibrillary plate appeared to calcify by invasion of crystals from the upper calcified zone into spaces between collagen fibers.

The wrist joint of two-toed sloths and its relevance to brachiating adaptations in the hominoidea.

Abstract: Two-toed sloths have evolved a wrist complex that includes the following traits: (1) diminution and distal migration of the pisiform, with a loss of contact with the ulna; (2) reduction of the distal end of the ulna to a styloid process; and (3) extremely reduced contact between the ulna and triquetrum. These traits were proposed by Lewis ('65, '74) to be indicative of brachiating habits and to be a unique adaptation of the Hominoidea. Cartmill and Milton ('77) recently found a similar complex in the wrists of the lorisines. Very similar adaptations of the wrist among the Hominoidea, lorisines, and two-toed sloths clearly refute contentions of Lewis and strengthen the hypothesis of Cartmill and Milton that the traits common to those animals are due to similar slow, cautious, but acrobatic locomotion.

Avian scale development. VI. Ultrastructure of the keratinizing cells of reticulate scales.

Abstract: Reticulate scales develop as radial symmetrical anlagen, in contrast to scuttate scales which appear initially as "epidermal placodes." Unlike scuttate scales whose outer and inner epidermal surfaces elaborate β-and α-type keratins, respectively, reticulate scales elaborate only one type of epidermal surface which has been reported to give an α-type, X-ray diffraction pattern. We find that, histologically and ultrastructurally, this surface differs from either epidermal surface of scuttate scales. The keratinizing cells become filled with long interweaving bundles of α-filaments which aggregate into rather homogeneous α-fibrils. Keratohyalin granules, which have been shown to be associated with other keratinizing regions in the bird, do not form during the keratinization of reticulate scale epidermis.

Fine structure of the gills of some Indian air-breathing fishes

Abstract: A detailed account is given of the structure of the gills of Clarias batrachus, Heteropneustes (= Saccobranchus) fossilis, Channa punctata, Monopterus (= Amphipnous) cuchia and Boleophthalmus boddaerti, based upon light and electron microscopy. In all five species the basic organization into primary and secondary lamellae is apparent but the latter are very much more modified in Monopterus. Three main layers separate the water and blood on the surface of the secondary lamellae. The outer epithelium is usually two layered but may be multilayered close to the origin of the secondary lamellae from the gill filament. The basement membrane is relatively thin and a middle dense layer containing collagen fibrils separates two clear layers. The pillar cells, so characteristic of secondary lamellae, are present in all except Monopterus and flanges from these cells surround the blood channels with the exception of the marginal channels. The latter are lined by endothelial cells which line all the blood channels of Monopterus. The overall thickness of the three layers comprising the water/blood barrier ranges from 1.5 to 13 microns. A number of modifications to this basic organization can be related to the degree of dependence of the different species on air-breathing. Boleophthalmus is the only species commonly found in brackish water and its secondary lamellae have well developed lymphoid spaces between two layers of the epithelium. Special densely-stained regions of the pillar cell flanges were also present in this fish and may have a supporting function.

Tooth crown morphology in caecilians (Amphibia: Gymnophiona).

Abstract: The morphology of tooth crowns is variable inter-specifically among caecilians. Cusp number and shape, crown dimensions, and crown curvature characterize various species and have both functional and phylogenetic implications. Ichthyophis, Uraeotyphlus, Hypogeophis, and Geotrypetes have bicuspid teeth; Dermophis, Gymnopis, Caecilia, and Typhlonectes monocuspid. Crown morphology as revealed by scanning electron microscopy is associated with prey grasping and, in one case, possible specialization of prey type.

The telotrophic-meroistic ovary of megaloptera. I. The ontogenetic development.

Abstract: Sialis flavilatera L. (Sialidae, Megaloptera) has telotrophic-meroistic ovarioles. The germ cells of the tropharium are organized into two distinct tissues, the central syncytium and the germ cell tapetum. The central syncytium consists of nurse cell nuclei embedded in a common cytoplasm which is rich in ribosomes and mitochondria. Cell membranes are totally absent. The germ cell tapetum surrounds the syncytium and consists of a monolayer of cells, each of which is connected with the central syncytium by an intercellular bridge. The oocytes differentiate from basal tapetum cells by previtellogenic growth. Their nutritive cords remain connected to the central syncytium by the intercellular bridge. Ovariole development starts soon after hatching with the immigration of germ cells into the ovariole-anlagen and is finished during pupal stages 23 months later. In apical regions of each tropharium, mitoses occur throughout larval life. The descendants enter the prophase of meiosis which lasts until pre-vitellogenesis; thus, a differential gradient of position and time is established. About 12 months after hatching, the central syncytium arises at the base of the tropharium from a membrane labyrinth in which intercellular bridges are entangled. Evidence is presented that endopolyploidization does not occur during germ cell differentiation. Finally, the results are compared with those found in Hemiptera and polyphage Coleoptera. The great diversities are interpreted as an indication for a polyphyletic origin of the telotrophic ovary.

Ultrastructure of the sacculus and lagena in a moray eel gymnothorax sp

Abstract: The ultrastructure of the sacculus and lagena of a moray eel, Gymnothorax sp., was investigated using scanning and transmission electron microscopy. Particular emphasis was placed on the orientation of the sensory hair cells and on the ultrastructure of the sensory cells. The ciliary bundles on the sensory hair cells are of several types, each having a different size relationship between the kinocilium and stereocilia. The cell bodies of the sensory cells are similar to the mammalian type II sensory cell. There were no apparent differences in the cell bodies between sensory cells with different ciliary bundles. Hair cell orientation patterns on the saccular and lagenar maculae differ from patterns found in other fishes. The posterior side of the saccular macula in Gymnothorax has cells oriented dorsally and ventrally, as is typical in other non-ostariophysan species. The anterior end of the saccular macula has alternating groups of anteriorly and posteriorly oriented cells, a situation that differs from the more typical pattern in which anteriorly oriented cells are found on the ventral side of the macula while posteriorly oriented cells cover the dorsal side of the macula. The orientation of cells on the lagena includes ventral cells that are located above a group of dorsally oriented cells. In many other non-ostariophysans, ventrally oriented cells are generally posterior to the dorsally oriented cells.

Ultrastructure of the bone marrow of the salamander Plethodon glutinosus (Caudata: Plethodontidae).

Abstract: The unusual lymphogranulopoietic bone marrow of the large lungless salamander Plethodon glutinosus was examined by light and electron microscopy. Developing neutrophils, eosinophils, and fat cells were found in large numbers, while lymphocytes of various sizes, plasma cells, plasmablasts, macrophages, pigment cells, and fibroblasts were present in more moderate numbers. Basophils were observed only rarely. Macrophages were found in extravascular locations and did not appear to be associated directly with the walls of the blood vessels supplying the marrow. Both neutrophils and eosinophils seemed to arise from small precursor cells whose ultrastructural features bore a resemblance in some ways to those of mammalian myeloblasts described by Bainton and Farquhar ('66). Developing neutrophils and eosinophils seemed to produce only single populations of specific cytoplasmic granules, rather than both primary (azurophilic) and secondary (specific) inclusions, as are produced typically by mammalian granulocytes. Both eosinophilic and neutrophilic granules were formed in association with Golgi complexes; and eosinophilic granules were much larger, more densely stained, and more regularly rounded in shape than the inclusions of developing neutrophils. Peroxidase activity was associated with the specific granules of neutrophils but seemed to be lacking in the granules of eosinophils. The specific granules of eosinophils were especially unusual because they contained irregularly shaped, lightly stained cores which occasionally displayed a distinctly crystalline substructural organization. The specific granules of basophils also possessed a prominent crystalline organization. The overall appearance of the marrow of Plethodon suggests that it functions not only as a valuable source of neutrophils, eosinophils, and cells of the lymphoid series, but also as a part of the phagocytic system of the animals and as an important repository for fat.

Cell death and optic fiber penetration in the optic stalk of the chick

Abstract: The role of dying cells in the optic stalk in relation to retinal fiber migration was investigated in the chick embryo. Cell death was analysed at various stages of development by counting pycnotic nuclei and also by the Gomori acid phosphatase reaction, while nerve fibers were visualised by the Bodian method. A wave of cell death, beginning in the neural retina at stage 18 and advancing with time through the stalk towards the diencephalon, occurred simultaneously or slightly prior to differentiation and migration of ganglion cell axons. Cell death stopped and gliogenesis occurred in the stalk after penetration by retinal fibers. Cell death occurred in the stalk even when fiber penetration was prevented by optic cup ablation. In this case, necrosis ensued until almost complete degeneration of the stalk, usually within three days after the operation, and gliogenesis did not occur. As the stalk degenerated, its cells became heavily pigmented. These observations suggest that the onset of cell death in the optic stalk is determined prior to and independently of retinal fiber penetration. On the other hand, cessation of cell death and subsequent gliogenesis occur only in the presence of ingrowing optic fibers.

Ultrastructural features of the retina and optic nerve of Strombus luhuanus, a marine gastropod

Abstract: The retina and optic nerve of Strombus luhuanus were examined by transmission electron microscopy in order to provide an ultrastructural basis for their electrophysiological responses, described elsewhere. The retina exhibits a distinct rhabdomeric layer and layers of cell nuclei and neuropile. These layers are comprised predominantly of three cell types that can be readily distinguished on the basis of their shape, their nuclei and cytoplasmic inclusions such as vesicles and filaments. One type of cell, apparently a photoreceptor that depolarizes in response to photic stimulation, possesses a long distal segment with microvilli; such distal segments comprise the bulk of the rhabdomeric layer. A second cell type, which appears to be supportive in function, contains a bundle of tightly packed tonofilaments that extend across the retina from the capsule to the vitreous body; this cell is quite narrow except in the region near the rhabdomeric layer, where it is expanded and wraps around the other cell types. A third type of cell possesses many short microvilli that project from its apical end into the rhabdomeric layer; it may be a second type of photoreceptor or another type of neuron. The retina also contains bundles of cilia that appear to project from a possible fourth type of cell. The layer of neuropile contains numerous processes that exhibit a variety of vesicle types and structures generally associated with synapses; these appear to play a role in mediating inhibitory and excitatory interactions between the retinal neurons. The optic nerve exhibits two populations of fiber distinguishable on the basis of mean diameter. Fibers in these two populations apparently yield "on" and "off" discharges in response to photic stimulation of the eye.

Surface morphology and functions of pharyngeal structures in the larval lamprey Petromyzon marinus.

Abstract: To gain insight into the multiple functions of a complex biological structure, the morphology of the pharynx of the larva (ammocoete) of the lamprey Petromyzon marinus was investigated with scanning electron microscopy and histochemistry (PAS and Alcian blue). Features studied include the gills, the parabranchial chambers external to the gills, intrapharyngeal ciliary tracts, the ridged pharyngeal roof, the floor, and the intrapharyngeal taste buds. Significant findings are: (1) All (nonciliated) cells lining these structures are covered with microvilli or microridges. The pattern and packing density of these membrane features vary among different pharyngeal structures. The lumenar membranes of pharyngeal lining cells overlie a mucous prosecretion in the apical cytoplasm, suggesting that the microvilli/ridges on these membranes function to anchor mucus. (2) Patterns of microvilli/ridges on the gill respiratory lamellae differ among ammocoetes of different species. (3) Pharyngeal osmo-regulatory cells (“chloride cells”) could not be identified on the basis of the microvillus/ridge pattern. (4) Two types of ciliary tracts are present within the pharynx. One has tall (x= 13 μm) and densely packed cilia, whereas the other has shorter (x= 7 μm) and less densely packed ones. Because mucus covers both types of tracts their function appears to involve the transport of mucus. (5) Food particles were found on the lateral surfaces of the gill filaments and on the surfaces of the parabranchial chambers. It appears that goblet cells in the epithelia of these regions secrete mucus in which the particles are trapped.

Microanatomy of the lung parenchyma of a tegu lizard Tupinambis nigropunctatus

Abstract: The combined techniques of light microscopy, scanning (SEM) and transmission (TEM) electron microscopy were used for the first time to study the structure of unicameral lungs of a Tegu lizard (Tupinambis nigropunctatus). The lungs are prolate spheroid bags with blood supplied by superficial branches of a dorsal pulmonary artery and returned by diffuse, more deeply located veins. The primary bronchus enters the medial aspect near the apex of the lung. The lung wall is composed of trabeculae: (1) arranged in a faviform pattern, (2) forming individual faveoli (gas exchange chambers) which appear deepest in the cranial one-half of the lung, (3) all of which have a smooth muscle core overlain by either a ciliated or nonciliated epithelium. A ciliated epithelium lines the luminal surfaces of the large primary trabeculae and parts of smaller secondary trabeculae; it is composed of cone-shaped cells with ciliated-microvillous surfaces, and of columnar serous secreting cells. Nonciliated epithelium covers the luminal surface of portions of some secondary trabeculae, abluminal surfaces of primary and secondary trabeculae and all surfaces of the small tertiary trabeculae forming the faveoli. The nonciliated epithelium overlies an extensive superficial capillary network. The blood-gas barrier (0.7-1.0 μm thick) is composed of a thin cytoplasmic flange of Type I pneumonocytes, a thick homogeneous basal lamina and an attenuated endothelial cytoplasm. Numerous surfactant-producing Type II pneumonocytes are closely associated with the Type I pneumonocytes. The nonrespiratory ciliated epithelium may function in humidification of air and clearing of the lungs.