bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative analysis of intramembranous particles in the membranous system of rat liver cells at different stages of development and aging
Authors: Goldhahn Achim , Robenek Horst , Fleischer Martin , Themann Hermann
Published: February 2005

The density of intramembranous protein particles was studied by freeze‐fracture. Particle density on the fracture faces of the plasmalemma and the rough endoplasmic reticulum (RER), as well as the outer and inner membranes of the nucleus and the mitochondria in rat hepatocytes were quantified. Comparison among different age groups sampled days postcoitum (dpc), days postpartum (dpp), and months postpartum (mpp) shows age‐related changes in particle density in each membrane system. With the exception of the RER, particle densities increased after the 16th dpc, reached a maximum at birth, and then decreased with increasing age. Simultaneously, the number nuclear pores shows a positive correlation with the particle density of the nuclear membranes. The particle density on the membranes of the RER shows a maximum on the 16th dpc, and on the 6th dpp. Thereafter, the density of the RER decreases slightly. In all membrane systems, the density of the particles on the external fracture faces is more variable than the density of the particles on the protoplasmic fracture faces.
Consequences of cell death after nitrogen mustard treatment on skeletal pelvic fin morphogenesis in the trout, Salmo gairdneri (Pisces, teleostei)
Authors: Geraudie Jacqueline
Published: February 2005

Five concentrations of nitrogen mustard (methyl‐bis‐chlorethylamine) have been administrated to different stages of development of trout embryos (Salmo gairdneri), in order to study their effect on the formation of both pelvic fins soft tissue and skeleton. Sensitivity of epidermis and mesoderm toward this cytotoxic agent has been assessed histologically. Although both components are sensitive to nitrogen mustard, mesoderm is more sensitive than epidermis. These results are compared with the results of similar studies on tetrapod limb buds. The pelvic fin skeleton of some treated animals was doubly stained in toto for cartilage and bone by Alcian blue and alizarin, followed by clearing. Other specimens were processed for histological serial sections. Analysis included comparison of the following parameters: (1) dose of nitrogen mustard, (2) stage of fin bud development at the time of treatment, (3) importance of necrosis in the fin bud, and (4) abnormalities of the endoskeleton of the fin (pelvic girdle and radials) and of the dermal skeleton (lepidotrichia and actinotrichia) one month after the hatching of control animals. Results suggest (1) that material of endoskeleton and lepidotrichia are laid down simultaneously, and (2) that differentiation of actinotrichia is independent of differentiation in endoskeleton and lepidotrichia.
An ultrastructural study of spermatogenesis in the nudibranch mollusc Spurilla neapolitana
Authors: Eckelbarger Kevin J. , Eyster Linda S.
Published: February 2005

The ultrastructural features of spermatogenesis were investigated in the nudibranch mollusc Spurilla neapolitana. Sperm develop in the proximal half of numerous sac‐like acini which are radially arranged within about ten ovotestis lobes. Accessory cells line the inner wall of the testicular portion of each acinus and are connected to developing sperm by numerous desmosomes. Stages of spermatid development have been divided into precup, cup, postcup, and elogate stages depending on the general shape of the nucleus. Nuclear differentiation includes the formation of anterior and posterior nuclear plaques, condensation of chromatin fibrils into nuclear lamellae, the insertion of the developing flagellar axoneme into a shallow, nuclear implantation fossa, and eventual formation of an elongated sperm head with a terminal twist. Spermiogenesis also includes the differentiation of an anterior, perinuclear structure having the characteristics of an acrosome, the appearance of peculiar arrays of ER cisternae, and the fusion of mitochondria into a large mitochondrial derivative which eventually encircles the axoneme, forming a crystalline‐like periaxonemal sheath.
Localization of crustacean hyperglycemic hormone (CHH) in the X‐Organ sinus gland complex in the eyestalk of the crayfish, Astacus leptodactylus (Nordmann, 1842)
Authors: Gorgels‐Kallen Janine L. , van Herp Françlois
Published: February 2005

The eyestalk of Astacus leptodactylus is investigated immunocytochemically by light, fluorescence, and electron microscopy, using an antiserum raised against purified crustacean hyperglycemic hormone (CHH). CHH can be visualized in a group of neurosecretory perikarya on the medualla terminalis (medulla terminalis ganglionic X‐organ: MTGX), in fibers forming part of the MTGX‐sinus gland tractus, and in a considerable part of the axon terminals composing the sinus gland. Immunocytochemical combined with ultrastructural investigations led to the identification of the CHH‐producing cells and the CHH‐containing neurosecretory granule type.
Determination of temperature sensitive stages for sexual differentiation of the gonads in embryos of the turtle, Emys orbicularis
Authors: Pieau Claude , Dorizzi Mireille
Published: February 2005

In order to determine the temperature sensitive stages for sexual differentiation of the gonads in Emys orbicularis, eggs of this turtle were shifted at different stages of embryonic development from the male‐producing temperature of 25°C to the female‐producing temperature of 30°C and reciprocally. Based on the series of developmental stages described by Yntema (′68) for Chelydra serpentina, temperature begins to influence sexual differentiation of Emys orbicularis at stage 16, a stage in which the gonads are still histologically undifferentiated. Its action lasts over the first steps of histological differentiation of the gonads. The minimal exposure at 25°C required for male differentiation of all individuals extends from stage 16 to somewhat before stage 21. For 100% female differentiation, incubation at 30°C must be longer, from stage 16 to somewhat before stage 22. Shorter exposures at 25°C or 30°C during these periods result in different percentages of males, females, and intersexes. Our results show that there is a critical stage (stage 16) which is the same for both male and female differentiation of the gonads. The thermosensensitive periods are rather long, corresponding to 11–12 days at 25°C and 30°C.
An ultrastructural analysis of isolated basement membranes in the acellular renal cortex: A comparative study of human and laboratory animals
Authors: Carlson Edward C. , Kenney M. Cristina
Published: February 2005

Freshly harvested kidneys from New Zealand white rabbits, Sprague‐Dawley white rats, rhesus monkeys, and transplant‐quality human kidneys were used in this study. Minced renal cortical tissue blocks (<2 mm3) were treated with 1 mM EDTA, 3% Triton X‐100, 0.025% DNAse, and 4% sodium deoxycholate in an effort to remove all cellular elements and leave the extracellular matrix (ECM) intact. These preparations showed remarkable structural preservation and all components of the ECM, including basement membranes (BMs), maintained their in vivo histoarchitectural relationships. By light microscopy, at least four major BM types were recognizable, including Bowman's capsular BM (BCBM), tubular BM (TBM), glomerular BM (GBM), and peritubular capillary BM (PTCBM). Scanning electron microscopy demonstrated that, despite the lack of supporting interstitium, GBMs in human, monkey, and rat (and rabbit to a lesser degree) exhibit intrinsic structural rigidity such that their convoluted spheroidal shapes are maintained following cell removal. Transmission electron microscopy showed that major BM types are morphologically heterogeneous and vary markedly within and between species. Randomized measurements showed that isolated BM thicknesses (lamina densa only) compared favorably with those reported in cellular preparations. Mean thicknesses of GBMs were within normal ranges in all species with or without power transformations to reduce right‐sided skew of distribution curves. In all species, thickness of BCBM > TBM > GGBM > PTCBM. The striking morphologic heterogeneity of major BM types demonstrated in the acellular renal cortex is not surprising in view of recent biochemical analyses that show that BMs derived from different sources are compositionally disparate. We conclude that BMs should be evaluated and characterized individually and that morphologic definition of isolated BMs is necessary prior to further analysis.
Active supercontraction in rolling‐up muscles of Glomeris marginata (myriapoda, diplopoda)
Authors: Carnevali Maria Daniela Candia , Valvassori Roberto
Published: February 2005

The lateroventral muscles of Glomeris marginata keep the animal rolled up and are able to develop and maintain great tension. Their fibers are not equipped with a particularly strong contractile apparatus but can super‐contract. The sarcomere shortens its resting length by up 60% and in a typical supercontraction the thick filaments pass through the Z‐line into adjacent sarcomeres. The Z‐line structure changes according to the contraction state: It passes from a homogeneous, dense zig‐zag line in decontracted fibers to a rarified, vaguely outlined Z‐band in supercontracted fibers, in which it is possible to see actin and myosin filaments. The Z‐line is thus involved in an active expanding process and is functionally very different from the fragmented and discontinuous Z‐line of “classical” supercontracting muscles. The different meaning of the two cases of supercontraction is discussed.
Cytodifferentiation in the accessory glands of Tenebrio molitor. X. Ultrastructure of the tubular gland in the male pupa
Authors: Happ George M. , Happ Christine M.
Published: February 2005

The tubular accessory gland consists of a simple secretory epithelium surrounded by a muscular coat. Over the pupal instar, the gland increases ten‐fold in volume and 15‐fold in length. Pupal development is divisible into a phase of mitosis and one of cell growth. During the mitotic phase, cytoplasmic membranes are sparse and nuclei move toward the luminal face of the epithelium to undergo division. In the cell growth phase, the cells become more columnar, a few stacks of rough endoplasmic reticulum are formed, and small dense secretory vesicles appear near the apical surface. The hormonal control of the developmental sequence is discussed.
The bursa cloacae (Fabricii) of struthioniforms in comparison with the bursa of other birds
Authors: Von Rautenfeld D. Berens , Budras K.‐D.
Published: February 2005

The late embryonic and postembryonic genesis of the bursa cloacae (Fabricii) of struthioniforms and other birds is described and discussed. The bursa of ostrich and emu is a wall organ of the caudal cloacal chamber. The bursa of rhea is, like the bursa of Gallus, a cranial appendix of the proctodeum. Lobuli bursales of struthioniforms are composed of a peripheral pars lymphoepithelialis (PLE) and a central pars lymphoreticularis (PLR). By contrast, lobuli bursales of Gallus are composed of a peripheral PLR and a central PLE. The fine structure of the bursa of struthioniforms is described. Other than in Gallus, the apical cell association of the PLE of struthioniforms shows secretory granules. This study thus far does not answer in detail the question of how the imprinting mechanism of the B‐lymphocytes operates. It is assumed that they are imprinted in the PLE. Postcapillary venules in the PLR are responsible for the transport of B‐lymphocytes. Hormonal bursectomies have been made to get information about the involution of the bursa of struthioniforms. In these species, involution means a gradual metaplasia while in Gallus it means a complete degeneration of the bursa.
Localization of 3H‐estradiol in the reproductive organs of male and female baboons
Authors: Weaker Frank J. , Sheridan Peter J.
Published: February 2005

The uptake and retention of radiolabeled estradiol by both the male and female reproductive organs were examined in the baboon. Two male and two female baboons were injected intracardially with 1 μg/kg body weight of 3H‐estradiol and two animals, one male and one female, were injected with both labeled and 100 μg/kg body weight of unlabeled estradiol. One and a half hours after the injections, the animals were sacrificed and the uterus, cervix, vagina, oviduct, seminal vesicles, and prostate gland were removed and processed for autoradiography. The stratified squamous epithelia of the cervix and vagina demonstrated a light uptake of the label in the germinative, but not in the superficial cell layers. The columnar cells lining the oviduct and uterine glands were labeled, whereas the luminal epithelium of the uterus and the glandular epithelia of the seminal vesicles and prostate gland did not sequester the tritiated steroid. The interstitial cells of all the organs studied demonstrated a moderate to heavy uptake of the radioactivity, whereas the smooth muscle cells were lightly labeled except in the vagina, in which these cells displayed a moderate number of silver grains.
The conjugation junction of Tetrahymena: Its structure and development
Authors: Wolfe Jason
Published: February 2005

The conjugation junction of Tetrahymena has been examined by thin sections, freeze fracture preparations, and by scanning electron microscopy. The junction is formed where the anterior tips of the pairing cells attach to one another. The structure is essentially a large disk composed of two face‐to‐face plasma membranes separated by a gap of extracellular space measuring about 50 nm. Rows of intramembrane particles are present at the boundary between the junction and ordinary cell cortex. These particles form a ring around the junction. Subjacent to each membrane is a thick mottled layer of material. Pores form in the junction at sites of membrane fusion. Though wider than long, these structures are actually bridges of cytoplasm that connect the conjugating cells. Pores fall into certain size and shape classes, indicating that membrane fusion is highly controlled in this system. At the level of the cytoplasmic bridge the submembrane material is compact and electron‐dense. Changes in the structure of the epiplasmic layer have been monitored as the normal cortex is modified during tip transformation and through formation of the mature conjugation junction. Evidence is provided that the submembrane layer plays a significant role in the regulation of pore formation. This cytoskeletal structure may also limit the extent of membrane fusion, thus controlling the size of the cytoplasmic channels.
A structural analysis of the freshly extruded spermatophore from the lobster, Homarus americanus
Authors: Kooda‐Cisco Marcia J. , Talbot Prudence
Published: February 2005

Freshly extruded spermatophores from the lobster, Homarus americanus, were examined using light microscopy and scanning and transmission electron microscopy. The tubular spermatophore is trifoil in shape with two lobes tapered laterally from a third lobe situated ventrally. It is comprised of sperm surrounded by three acellular investments: (1) a primary spermatophore layer, (2) an intermediate layer, and (3) an outer bounding layer. The sperm are packed into a continuous tube contained largely within the ventral lobe and are embedded in a matrix of moderate electron density. The primary spermatophore layer is uniformly thick around the sperm mass and contains at its peripheral margins both ring structures and crystals in an amorphous matrix. The intermediate layer is thicker dorsally than ventrally. Dense granules dominate the ventral half of the intermediate layer while inclusions populate the dorsal half; both react positively to the periodic acid‐Schiff (PAS) technique. The innermost portion of the outer bounding layer is composed of parallel fibrils; a flocculent material is present peripherally. This flocculent substance is presumed to impart stickiness to freshly extruded spermatophores. These observations provide a basis for the future understanding of the mechanisms involved in long‐term storage of sperm in spermatophores.
Ultrastructural study of midgut embryonic cytodifferentiation in the phasmid Clitumnus extradentatus Br.
Authors: Kadiri Zineb , Louvet Jean‐Pierre
Published: February 2005

The embryonic cytodifferentiation of Clitumnus midgut occurs very late when compared to that of other tissues in the embryo. It proceeds from hemolymph towards the yolk, first at the level of the muscular–connective tissue sheath, by the appearance of myofilaments in external–then internal–muscle fibers. In the gut epithelium, cytodifferentiation begins with the appearance of infoldings of the basal membranes of the cells. Then, microvilli and continuous junctions form at the apices of the cells. Microvilli appear in crypts, which seem to represent localized dilatations of intercellular spaces. At the level of these crypts, continuous junctions are formed somewhat later than are microvilli. This midgut differentiation coincides with deposition of the third embryonic (first larval) cuticle, and with a high titer of ecdysteroids.
Mechanisms of rapid morphogenetic movements in the metamorphosis of the bryozoan Bugula neritina (cheilostomata, cellularioidea). I. Attachment to the substratum
Authors: Reed Christopher G. , Woollacott Robert M.
Published: February 2005

The larval morphology, settlement behavior, and the rapid morphogenetic movements that occur during the first 60 sec of metamorphosis of the cellularioid cheilostome bryozoan Bugula neritina have been examined and analyzed by light and electron microscopy. The larva attaches to the substratum at the onset of metamorphosis by the eversion of the internal sac. At the same time, the coronal cilia reverse their direction of beat, spreading an adhesive secreted by the neck region of the everting sac over the metamorphosing larva. During attachment, the larva goes through several configurations that coincide with the sequential contraction and relaxation of certain larval muscles. Histological and ultrastructural evidence indicates that the neck and wall regions of the internal sac are everted by the contraction of the muscles in the equatorial plane of the larva at the same time that the roof region in pulled toward the larval equator by the contraction of the axial muscles. The subsequent relaxation of the axial muscles allows the roof region to be everted by the antagonistic force generated by the sustained contraction of the equatorial musculature. After the roof region attaches to the substratum, the apical disc is temporarily retracted by a second contraction of the axial muscles. The apical disc subsequently reextends as the axial muscles relax just before coronal involution. A comparison of the ontogenetic sequence of rapid morphogenetic movements in the metamorphoses of cheilostome and ctenostome bryozoans indicates that cellularioid cheilostomes have undergone peramorphosis in the aspect of development.
An ultrastructural study of the development of the dermal iridophores and structural pigmentation in Poecilia reticulata (peters)
Authors: Gundersen R. E. , Rivera E. R.
Published: February 2005

Three general stages of iridophore development were found in Poecilia reticulata that correspond to the development of structural pigmentation. The first stage was prevalent in fish embryos about to hatch to young fish 4 months old. Dermal cells containing elements of endoplasmic reticulum and a Golgi apparatus developed into iridophores. The endoplasmic reticulum early in iridophore development became a few sparse cisternae, and the Golgi apparatus elaborated long rectangular vacuoles with two membranes. From 5 to 15 vacuoles were arranged in parallel stacks in each developing iridophore. Crystals of guanine were deposited within the inner compartment of each vacuole. At this stage of development, the young fish had only a few dermal iridophores next to the lateral muscle. Fish 4 to 6 months old had a more advanced type of iridophore development including several layers of iridophore cells in the dermis. The innermost iridophores near the muscle had many mature crystal‐containing vacuoles (iridosomes). Each cell had upt to three stacks of 10–20 iridosomes with their long axis oriented at a slight oblique angle to the surface of the fish. The outer layers of iridophores resembled the immature developing cells found in very young fish. The third developmental stage was found in sexually functional adults. All dermal iridophores contained 2–3 groups of 10–20 mature iridosomes. In mature iridophores, the Golgi apparatus was not found in the cytoplasm. The thickness of the guanine crystals (70 nm) and cytoplasmic intervals (90 nm) results in a constructive interference reflection of 496 nm (blue‐green). This iridescence increased concomitantly with the increase in iridophore cells in the dermis and the maturation of their iridosomes.
Ultrastructure of the pineal gland of the eastern chipmunk (Tamias striatus)
Authors: Karasek Michal , King Thomas S. , Hansen John T. , Reiter Russel J.
Published: February 2005

The ultrastructure of the pineal gland of the wild‐captured eastern chipmunk (Tamias striatus) was examined. A homogenous population of pinealocytes was the characteristic cellular element of the chipmunk pineal gland. Often, pinealocytes showed a folliclelike arrangement. Mitochondria, Golgi apparatus, granular endoplasmic reticulum, lysosomes, centrioles, dense‐core vesicles, clear vesicles, glycogen particles, and microtubules were consistent components of the pinealocyte cytoplasm. The extraordinary ultrastructural feature of the chipmunk pinealocyte was the presence of extremely large numbers of “synaptic” ribbons. The number of “synaptic” ribbons in this species exceeded by a factor of five to 30 times that found in any species previously reported. In addition to pinealocytes, the pineal parenchyma contained glial cells (oligodendrocytes and fibrous astrocytes). Capillaries of the pineal gland of the chipmunk consisted of a fenestrated endothelium. Adrenergic nerve terminals were relatively sparse.
The photoreceptors of the west indian manatee
Authors: Cohen Joel L. , Tucker Gail S. , Odell Daniel K.
Published: February 2005

Using light and electron microscopy we found that the manatee retina has both rodlike and conelike photoreceptors in accord with its diurnal behavior pattern. Outer segment disks in both cell types appear to be enclosed along most of their length within the plasma membrane. The synaptic terminals are simple, with small, superficial postsynaptic contacts. The cones have long inner segments, short, conical outer segments and terminals with numerous synaptic ribbons and deeply embedded postsynaptic elements. There are two cone subclasses that may subserve color vision. Morphometry shows that there are more ganglion cells of small size ventrally, and that the thickness of the nerve fiber layer there is reduced, suggesting the presence of a specialized visual area in the retina. However, there were no pronounced differences in cone cell density in any of the regions examined.
Development of the musculus levator externus IV and the musculus obliquus posterior in Haplochromis elegans trewavas, 1933 (teleostei:Cichlidae): A discussion on the shift hypothesis
Authors: Aerts Peter
Published: February 2005

An ontogenetic study of several postembryonic stages of Haplochromis elegans shows that the muscle referred to as “musculus levator externus IV” by previous authors in the adult stage of cichlid fishes is a compound muscle composed of the M. levator externus IV and the central portion of the M. obliquus posterior. Thus the supposed shift of the insertion area of the fourth external levator muscle from the fourth epibranchial to the fifth ceratobranchial, as deduced from adult morphology only, did not occur. Although this ontogenetic discovery does not change the functional specializations ascribed to the muscle by previous authors, it could have very important implications for the phylogenetic placement of the Cichlidae relative to such major taxa as Labroidei and Embiotocidae.
The cellular basis of the aggressive acrorhagial response of sea anemones
Authors: Bigger Charles H.
Published: February 2005

Some sea anemones possess structures called acrorhagi at the base of the tentacles. The acrorhagi are utilized solely for aggression. Acrorhagial aggression involves very exquisite intra‐ and interspecific recognition. This study examined acrorhagi and putative acrorhagial analogues or homologues in four species of sea anemone. The morphology and ultrastructure of tentacles, pseudoacrorhagi, column vesicles, and verrucae (adhesive column vesicles) differed from that of acrorhagi. Coral capitate tentacles and acrorhagi have different surface morphology, nematocysts, and functions. Besed on morphology, acrorhagi seem more likely to be homologous to tentacles than to verrucae.

Acrorhagial nematocyst discharge and ectodermal peeling, the culmination of the response, were shown to require prior acrorhagial expansion in Anthopleura krebsi and Bunodosoma cavernata. A mechanical mechanism is suggested where‐ by distention of the acrorhagus opens a ciliary pit on the nematocyte surface and exposes the pit wall and microvilli, which may contain the chemoreceptors for the peeling process, including nematocyst discharge. A similar system may also be responsible for changing the threshold of nematocyst discharge in sea anemone tentacles. A case of possible neurosecretion in an anthozoan was also shown in this study.
The architecture of the spleen of the red‐eared slider, Chrysemys scripta elegans (reptilia, testudines)
Authors: Kroese F. G. M. , Van Rooijen N.
Published: February 2005

The morphology of the spleen of the Red‐eared Slider, Chrysemys scripta elegans, has been described. The outer surface of the spleen is covered by a thin fibromuscular capsule, from which a number of trabeculae extend into the parenchyma. The parenchyma of the spleen shows a definite demarcation into a red and white pulp. The white pulp is composed of two lymphoid compartments: lymphoid tissue surrounds both central arterioles and ellipsoids, forming the periarteriolar and periellipsoidal lymphocyte sheath (PALS and PELS, respectively). The ellipsoids consist of a thick layer of reticular tissue, enclosing a capillary with cuboidal endothelium. In contrast with the PALS, reticular fibers are rarely found in the PELS. Even after severe stimulation with paratyphoid vaccine, germinal centers are not found in the spleen of C.s. elegans. The red pulp of the spleen is composed of a system of venous sinuses and cords.
The organization of the reptilian brainstem reticular formation: A comparative study using Nissl and Golgi techniques
Authors: Newman Donald B. , Cruce William L. R.
Published: February 2005

The brainstem reticular formation has been studied in 16 genera representing 11 families of reptiles. Measurements of Nissl‐stained reticular neurons revealed that they are distributed along a continuum, ranging in length from 10 μm to 95 μm. Reticular neurons in crocodilians and snakes tend to be larger than those found in lizards and turtles. Golgi studies revealed that reticular neurons posess long, rectilinear, sparsely branching dendrites. Small reticular neurons ( > 31 μm length) possess fusiform or triangular somata which bear two or three primary dendrites. These dendrites have a somewhat simpler ramification pattern when compared with those of large reticular neurons (< 30 μm length). Large reticular neurons generally possess perikarya which are triangular or polygonal in shape. The somata of large reticular neurons bear an average of four primary dendrites. The dendrites of reptilian reticular neurons ramify predominantly in the transverse plane and are devoid of spines or excrescences. The dendritic ramification patterns observed in the various repitilian reticular nuclei were correlated with known input and output connections of these nuclei.

Nissl and Golgi techniques were used to divide the reticular formation into seven nuclei. A nucleus reticularis inferior (RI) is found in the myelencephalon, a reticularis medius (RM) in the caudal two‐thirds of the metencephalon, and a reticularis superior (RS) in the rostral metencephalon and caudal mesencephalon. Reticularis inferior can be subdivided into a dorsal portion (RID) and a ventral portion (RIV). All reptilian groups possess RID and RM but RIV is lacking in turtles. Reticularis superior can be subdivided into a large‐celled lateral portion (RSL) and a small‐celled medial portion (RSM). All reptilian groups possess RSM and RSL, but RSL is quite variable in appearance, being best developed in snakes and crocodilians. The myelencephalic raphe nucleus is also quite variable in its morphology among the different reptilian families. A seventh reticular nucleus, reticularis ventrolateralis (RVL), is found only in snakes and in teiid lizards. It was noted that the reticular formation is simpler (fewer numbers of nuclei) in the representatives of older reptilian lineages and more complex (greater numbers of nuclei) in the more modern lineages. Certain reticular nuclei are present or more extensive in those families which have prominent axial musculature.
Appendicular skeletal morphology in minute salamanders, genus Thorius (amphibia: Plethodontidae): Growth regulation, adult size determination, and natural variation
Authors: Hanken James
Published: February 2005

Patterns of growth and variation of the appendicular skeleton were examined in Thorius, a speciose genus of minute terrestrial plethodontid salamanders from southern Mexico. Observations were based primarily on ontogenetic series of each of five species that collectively span the range of adult body size in the genus; samples of adults of each of seven additional species provided supplemental estimates of the full range of variation of limb skeletal morphology.

Limbs are generally reduced, i.e., pedomorphic, in both overall size and development, and they are characterized by a pattern of extreme variation in the composition of the limb skeleton, especially mesopodial elements, both within and between species. Fifteen different combinations of fused carpal or tarsal elements are variably present in the genus, producing at least 18 different overall carpal or tarsal arrangements, many of which occur in no other plethodontid genus. As many as four carpal or tarsal arrangements were observed in single population samples of each of several; five tarsal arrangements were observed in one population of T. minutissimus. Left‐right asymmetry of mesopodial arrangement in a given specimen is also common.

In contrast, several unique, nonpedomorphic features of the limb skeleton, including ossification of the typically cartilaginous adult mesopodial elements and ontogenetic increase in the degree of ossification of long bones, are characteristic of all species and distinguish Thorius from most related genera. They form part of a mechanism of determinate skeletal growth that restricts skeletal growth after sexual maturity. Interspecific differences in the timing of the processes of appendicular skeletal maturation relative to body size are well correlated with interspecific differences in mean adult size and size at sexual maturity, suggesting that shifts in the timing of skeletal maturation provide a mechanism of achieving adult size differentiation among species.

Processes of skeletal maturation that confer determinate skeletal growth in Thorius are analogous to those typical of most amniotes – both groups exhibit ontogenetic reduction and eventual disappearance of the complex of stratified layers of proliferating and maturing cartilage in long bone epiphyses – but, unlike most amniotes, Thorius lacks secondary ossification centers. Thus, the presence of secondary ossification centers cannot be used as a criterion for establishing determinate skeletal growth in all vertebrates.
Synthesis of the vitelline and chorionic membranes of an ichneumonid parasitoid
Authors: Norton William N. , Vinson S. Bradleigh
Published: February 2005

A reduction in free ribosomes and increases in rough endoplasmic reticulum and Golgi complexes in follicle cells during oogenesis suggest their involvement in supplying precursor material for synthesis of the vitelline and chorionic membranes of the ichneumonid parasitoid Campoletis sonorensis. The inner region of the vitelline membrane is composed of a narrow band of electron‐opaque material; an outer region adjacent to the chorion consists of overlapping, irregularly shaped laminae. The fully developed chorion can be divided morphologically into three distinct regions. Its inner region adjacent to the lamellar plates of the vitelline membrane is composed of a lamellar membrane exhibiting a regular periodicity of crossbands. The middle section is composed of longitudinal chambers, some of which contain particulate matter. The outer region consists of slender projections which extend perpendicularly from the chorion surface. A fine layer of fibrous material adheres to the projections. The possibility of a relationship between the presence of fibrous material on the surface of parasitoid eggs and the inactivation or inhibition of host immune systems is mentioned.
Structure of the shell from eggs of the tuatara, Sphenodon punctatus
Authors: Packard Mary J. , Hirsch Karl F. , Meyer‐Rochow V. B.
Published: February 2005

Shells from eggs of the tuatara (Sphenodon punctatus) are 0.2 mm thick and are composed of a layer of calcite and a multi‐layered, fibrous shell membrane. Most of the calcareous layer is composed of roughly circular columns of crystalline material that extend deep into the shell membrane. The crystalline matrix of the columns is interwoven with fibers of the shell membrane except near the outer surface of the eggshell, where the calcareous material is more compact. Overlying the columns is a granular layer composed of blocks of crystalline material of random size, shape, and orientation. Disruption of this granular layer, perhaps through swelling of the eggs or as a result of environmental factors, gives the outer surface of the eggshell a coarse, weathered appearance. Removal of the calcareous material with a decalcifying agent shows that the outer surface of the shell membrane is composed of a meshwork of small fibers bound together by an amorphous matrix. No matrix was observed in inner layers of the shell membrane, and the fibers of these inner layers are arranged somewhat more regularly than the outer fibers. No structure comparable to the central cores of avian and certain chelonian eggs was observed in eggshells of the tuatara.
Electromyography of the opercularis muscle of Rana catesbeiana: An amphibian tonic muscle
Authors: Hetherington Thomas E. , Lombard R. Eric
Published: February 2005

The opercularis muscle of Rana catesbeiana originates on the suprascapular cartilage of the shoulder girdle and inserts on the otic opercular element. It is part of the levator scapulae musculature and lies dorsomedial to the levator scapulae superior and inferior muscles. Bipolar electrode recordings from all three muscles show electrical activity linked to cyclical firing of the posterior intermandibularis muscle, an important ventilatory muscle. The opercularis muscle shows low amplitude, erratic signals when animals are sumerged. Upon emergence of the snout region, the opercularis muscle shows rhythmic low amplitude activity at twice the rate of buccal pumping. Lung ventilation is synchronized with this rhythm and at ventilation the opercularis muscle shows higher amplitude activity. Upon submergence, opercularis activity again shows low level activity with no rhythmic pattern. Opercularis muscle activity has a major low frequency component (about 30 Hz) that probably corresponds to activity of tonic muscle fibers. Higher frequency signals (about 200–250 Hz) comparable to those of the levator scapulae muscles are also present and probably represent activity of phasic muscle fibers. Activity of the opercularis muscle is correlated with conditions in which aerial respiration is possible, and this pattern of activity supports an opercularis role in aerial hearing and/or detection of substrate vibrations. As far as we know, this is the first report of electromyographic analysis of a vertebrate tonic muscle.
Terminal airway embryology of the delphinid porpoises, Stenella attenuata and S. longirostris
Authors: Drabek Charles M. , Kooyman Gerald L.
Published: February 2005

A light microscopic investigation of the histological development of the terminal airways of 18 Stenella attenuata and two S. longirostris showed the lungs to be in a glandular stage of development until 3 months postimplantation (p.i.) age. By 3.5 months (p.i.) the lung was at the canalicular stage. At 4 months mesenchymal rings and muscular bands were in a sphincterlike arrangement around terminal bronchioles. At 7 months (p.i.) the alveolar stage occured. About 8–9 months cartilaginous rings were present and in association with myoelastic sphincters. Their function remains an enigma, even though many hypotheses as to function have been proposed. We suggest that the presence of well‐developed sphincters and cartilage in the neonate may give clues to their function as well as offer potential experiments that would not be as suitable in the adult porpoise.
Ultrastructure of the tubular nephron of the lizard Podarcis (= Lacerta) Taurica
Authors: Gabri M. S.
Published: February 2005

The proximal, intermediate, and distal convoluted tubules of the neprhon of Podarcis (= Lacerta) taurica were examined by electron microscopy. Proximal tubule cells have large, apical cytoplasmic protrusions and microvilli interpreted to function in urate secretion. Adjacent cells are bound apically by tight junctions and desmosomes but interdigitate in their basal region. This situation is repeated in the other tubules with significant differences in intercellular space width. The basal surfaces bear numerous cytoplasmic processes. The intermediate tubule has proximal and distal segments each with dark, ciliated, and light cells, the cuboidal dark cells with dense cytoplasm constituting the main bulk of the wall. As the cells of the proximal and distal segments resemble those of the proximal and distal convoluted tubules, respectively, the intermediate tubule is considered as a transition region. The ciliated cell body has two broad processes extending from the lumen, one to the basement membrane and one to a foot process of a light cell. The light cell is surrounded by dark and ciliated cells. It does not reach the lumen, but contacts the basement membrane through a process running below a ciliated cell to form a mushroom‐shaped structure in tubule cross‐section, the light cell process forming the stalk and a ciliated cell the cap. The cilia probably propel the glomerular filtrate towards the distal convoluted tubule. This latter tubule has initial, middle, and terminal zones, all nonciliated but with different lumen widths and cell shapes.
Histochemical and ultrastructural features of the epidermis of the land planarian Bipalium adventitium
Authors: Curtis Sherill K. , Cowden Ronald R. , Moore J. D. , Robertson J. Leonard
Published: February 2005

The epidermis of the land planarian Bipalium adventitium was examined by light and electron microscopy. In all regions, the epidermis consists of a simple columnar ciliated epithelium associated with a prominent basement membrane. The epithelial cells, possessing abundant microvilli and poorly developed terminal webs, are conjoined laterally at their apical ends by septate junctions. The epidermis of the creeping sole is distinguished from that of adjoining regions by a “insunken” condition of the epithelial cells, a greater number of cilia per cell, and an absence of glandular secretions other than mucus. The insunken cells of the sole possess large glycogen disposits and attributes of metabolically active cells. Unusual intranuclear inclusions of unknown significance are also found in many of the epidermal cells in all regions. The basement membrane lacks distinct layering and consists of fine fibrils displaying a beaded appearance but no obvious cross‐banding. Histochemical tests indicate that the fibrils are collagenous. In addition to mucus, secretory material found in nonsole regions includes lamellated granules and rhabdites, both stained intensely by acidic dyes. Rhabdites and the basement membrane also contain disulfide‐enriched proteins. In scanning electron micrographs, the sole appears as a faint, longitudinally oriented band extending along the entire length of the animal. In all regions except the sensory border of the head, the microvilli are generally obscured by the densely arranged cilia. The sensory border consists of a row of toothlike papillae and grooves covered almost exclusively by microvilli, small club‐shaped structures, and larger spherical protrusions.
The sensory systems and feeding behavior of leafhoppers. II. A comparison of the sensillar morphologies of several species (Homoptera: Cicadellidae)
Authors: Backus Elaine A. , McLean Donald L.
Published: February 2005

The ultrastructure of the sensilla, and other structures, within the precibaria of eight species from three subfamilies of leafhoppers (Homoptera: Cicadellidae) were examined with scanning electron microscopy. The types and grouping of the 20 precibarial sensilla in seven of these species were similar to those observed previously in Macrosteles fascifrons Stål. Oncometopia nigricans (Walker) also displayed similar sensilla groups; however, it had 30 sensilla. The species examined differed chiefly in the exact location and arrangement of the sensilla. The possible significance of the differences relative to leafhopper feeding is discussed. The precibarial chemosensilla may provide chemosensory evaluation of fluid in the food canal and precibarium prior to ingestion or egestion.
Early ontogeny of the annual fish genus Nothobranchius: Cleavage plane orientation and epiboly
Authors: van Haarlem Robert
Published: February 2005

Living embryos of ten species of the teleost fish Nothobranchius were observed from fertilization through the ten‐somite stage. Cellular behaviour during early development showed differences as well as similarities among species. In one species at the eight‐cell stage the blastomeres are arranged in two rows of four cells, all in one plane. In three other species the blastomeres are arranged in two layers of four cells, each one above the other, and in the remaining six species the arrangement is intermediate between the one‐layer and two‐layer pattern. Hybridization experiments showed that the sequence of orientation of cleavage planes is not under the control of either the nucleus or of cytoplasmic factors from the sperm. At midcleavage stages, marginal cells of the blastoderm undergo fusion, thus giving rise to the external‐Yolk Syncytial Layer. A second period of fusion of cells of the Enveloping Layer occurs just before epiboly starts and a third one after epiboly has concluded. Marginal cells of the Enveloping Layer do not possess cell protrusions such as blebs, lobopodia, or filopodia; therefore, spreading of the Enveloping Layer during epiboly by means of locomotion of marginal cells seems unlikely. Evidence is presented that the deep cells within the segmentation cavity remain separated from one another through contact inhibition during epiboly and that they use the Enveloping Layer as a substratum during their dispersion over the yolk. A description of normal stages applicable to all ten species of Nothobranchius is presented.
Cleavage in vivo and in culture in the dasyurid marsupial Antechinus stuartii (macleay)
Authors: Selwood Lynne , Young G. J.
Published: February 2005

Cleavage in the brown marsupial mouse, Antechinus stuartii, from the zygote to the unilaminar blastocyst, was observed in vivo and in culture and in sections of embryos. The first three divisions were meridional and passed from the yolk pole to the opposite pole. Deutoplasmolysis, resulting in a distinct yolk mass, occurred during the first two divisions. Prior to the third and fourth divisions, the blastomeres elongated and flattened against the zona pellucida. The fourth division was latitudinal and resulted in two histologically distinct rings of eight blastomeres which were at first rounded and then became flattened against the zona. Further divisions and flattening of the blastomeres resulted in a complete unilaminar blastocyst by the time the blastocyst numbered 22 to 30 cells. Some expansion, causing compression of the zona and mucoid layers, occurred before completion of the blastocyst, but most expansion occurred once the blastocyst was complete. No histological differences could be detected between the blastomeres at this stage. Embryos were successfully cultured from the zygote to the rounded four‐cell stage and from the flattened four‐cell stage to the completed unilaminar blastocyst of around 32 cells. Total estimated cleavage times were slower in culture than in vivo, but the relative lengths of time for each division were approximately the same.
A correlated light and electron microscopic study of the structure and secretory activity of the accessory salivary glands of the marine gastropods, Conus flavidus and C. vexillum (neogastropoda, conacea)
Authors: Schultz Michael C.
Published: February 2005

The structure and secretory activity of the accessory salivary gland in two species of Conus were examined using routine and histochemical techniques of light, scanning and transmission electron microscopy.

The composite layers of the accessory salivary gland of Conus are a luminal epithelium, fibromuscular layer, submuscular layer, and a capsule. In C. flavidus and C. vexillum, the luminal epithelium is formed by epitheliocytes and cytoplasmic processes extending from the secretory cells, whose perikarya form the submuscular layer. The processes carry secretory cell products (chiefly Golgi‐derived glycoprotein) across the fibromuscular layer and terminate between epitheliocytes (at the bases of the secretory canaliculi) or beyond the surface of the epithelial cells. Conus vexillum is distinguished from C. flavidus by its high content of lipofuscin. Epitheliocytes are the only microvillated cells in the accessory salivary gland of Conus. In C. flavidus, epitheliocytes extrude secretory granules, various types of cytoplasmic blebs and clear vesicles by apocrine “pinching off”. Clear vesicles are shed from the tips of microvilli. The luminal epithelial cells of C. vexillum similarly egest clear vesicles, but normally undergo additional holocrine secretion to release lipofuscin.

The secretions of epitheliocytes appear to be major products of the accessory salivary gland: consideration of secretory activities by both epitheliocytes and secretory cells will therefore be necessary when directly investigating accessory salivary gland function in Conus.
Thoracic morphology of a flightless mexican grasshopper, Barytettix psolus: Comparison with the locust, Schistocerca gregaria
Authors: Arbas Edmund A.
Published: February 2005

The thoracic morphology of a flightless grasshopper, Barytettix psolus, is described and compared to that of locusts, Schistocerca gregaria, to evaluate modifications to skeleton, muscles, and the nervous system which have accompanied secondary loss of flight. Barytettix lacks hindwings, has immobile vestiges of forewings and is devoid of skeletal specializations for wing movement and flight. Its pterothoracic musculature resembles that of Schistocerca except for the absence of those muscles which, in locusts, have the primary function of moving the wings, the dorsal longitudinal, tergosternal, first basalar, pleuroalar, and dorsal accessory muscles. Pterothoracic ganglia of Barytettix resemble those of Schistocerca in their gross features, number, and primary branching pattern of nerves, with differences in detail relating to reduction of the flight muscles. The combination of features exhibited in Barytettix represents an extreme reduction in the specialization for wing movements and flight displayed by most acridids, at a level which exceeds that of many brachypterous and some apterous species. While skeletal fusion and loss of muscles indicate loss of flight, the accompanying thoracic stiffening and increase in overall body density may promote more efficient jumping as a means of locomotion.