Histology and functional morphology of the oviduct of an oviparous snake,Diadophis punctatus

Oviductal functional morphology remains poorly understood in oviparous snakes, particularly in regard to oviductal formation of albumen and the eggshell and to sperm storage. The oviduct of Diadophis punctatus was examined using histology and scanning electron microscopy to determine oviductal functional morphology throughout the reproductive cycle. The oviduct is composed of four morphologically distinct regions: infundibulum, uterine tube, uterus, and vagina. The infundibulum is thin, flaccid, and lined with simple ciliated cuboidal epithelial cells. The tube contains ciliated and secretory epithelial cells, which reach a maximum height and hypertrophy during early gravidity and produce glycosaminoglycans. The posterior portion of the tube contains temporary sperm storage receptacles. The uterus retains eggs throughout gestation and secretes the eggshell constituents. The endometrial glands of the uterus hypertrophy during vitellogenesis and become depleted of the secretory granules during gravidity. The functional morphology of the oviduct therefore shows cyclical changes that are correlated with eggshell formation. The vagina consists of thick longitudinal and circular smooth muscle layers, which may serve in retention of eggs during gestation. Furthermore, the vagina contains long furrows in the mucosa that serve as sperm storage receptacles. These receptacles store sperm following fall mating and overwintering, whereas the receptacles in the tube are utilized briefly during vitellogenesis just prior to ovulation. © 1996 Wiley-Liss, Inc.     

Structure of the female gonoduct of the viviparous teleost Poecilia reticulata (Poeciliidae) during nongestation and gestation stages

Female teleosts do not have oviducts because Müllerian ducts do not develop. Instead, the caudal region of the ovary, the gonoduct, connects to the exterior. Because of the lack of oviducts in viviparous teleosts, the embryos develop in the ovary, as an intraovarian gestation, unique in vertebrates. This is the first study to address the histology of the gonoduct in a viviparous teleost. The gonoduct of Poecilia reticulata was analyzed during previtellogenesis, vitellogenesis, and gestation. The gonoduct lacks germinal cells. From deep to superficial, the wall has simple cuboidal or columnar epithelium, loose connective tissue, longitudinal layer of smooth muscle, and visceral peritoneum. Cells of the immune system occur in the lumen and in the mucosa. The gonoduct was divided in three regions: 1) cephalic, 2) middle, and 3) caudal. At the initial part of each region, thin mucosal folds extend into the lumen. The cephalic region forms a tubular structure with light and irregular folds. The middle region has a wider lumen and is more irregular due to ventral invaginations and irregular and short mucosal folds; beneath the epithelium there are melano‐macrophage centers. The caudal region is delimited from the middle region by folds; however, they are thinner than these of the other regions. Ventral invaginations form exocrine glands, and the smooth muscle is thicker than in the other regions. During gestation, cells of the immune system are abundant; melano‐macrophage centers become larger and the glands exhibit desquamated cells. These observations suggest roles of the gonoduct in reducing the diameter of the lumen; receiving sperm during vitellogenesis; producing secretions, more abundant during vitellogenesis; and in immunological activity throughout the reproductive cycle. The ciliated epithelium and the thick muscle of the caudal region may be involved during birth. J. Morphol. 275:247–257, 2014. © 2013 Wiley Periodicals, Inc.     

Three-dimensional cytoarchitecture of the media of arteriovenous anastomoses in the rabbit ear

Arteriovenous anastomoses in the rabbit ear were examined with scanning electron microscopy to elucidate the structural differentiation of the media of the shunt. Arterial, intermediate, and venous segments in the shunt and two layers of the media in the intermediate segment were differentiated based on cell shape and cell organization. In the arterial segment, smooth muscle cells were spindle-shaped, either elongated or short, with a few branches, and were arranged circularly or diagonally with respect to the vessel's long axis. There were also stellate muscle cells with radiating processes. In the intermediate segment, the smooth muscle cells of the outer layer of the media were also arranged circularly and resembled the elongated cells in the arterial segments, but they were more irregular in shape and had more processes than those of the arterial segment. The epithelioid cells of the inner layer of the media were oval or polygonal and oriented irregularly with respect to the vessel's long axis, clustering to form longitudinal plicae. The smooth muscle cells of the venous segment were flat with many lateral processes and formed a thin, discontinuous layer. The smooth muscle cells in the arterial segment and those of the outer layer of the intermediate segment exhibited a highly rugged surface texture, indicating their strong contractility; the epithelioid cells and the smooth muscle cells in the venous segment exhibited a generally smooth surface, indicating less contractility. The intermediate segments were supplied with a dense nerve plexus. The intermediate segments, therefore, may be actively involved in the regulation of blood flow under neuronal influence.     

Spontaneous and neurally evoked contractions of visceral muscles in the oviduct of Locusta migratoria

The oviducts of Locusta migratoria are innervated by a pair of nerves which arise from, the seventh abdominal ganglion. A distinctive network of striated muscle fibres occurs in the oviducts. The lateral oviducts and common oviduct consist of an inner circular layer of muscle and an outer longitudinal layer of muscle. At the junction of the lateral and common oviduct an additional thin longitudinal layer is found adjacent to the basement epithelium. The oviducts contracted spontaneously when isolated from the central nervous system. These myogenic contractions took the form of peristaltic contractions in the lateral oviduct, and intermittent phasic-like contractions of the posterior regions of the lateral oviduct and the common oviduct. These phasic-like contractions were associated with individual complex potentials recorded extracellularly from the muscle fibres. In locusts that had been interrupted in the process of egg laying, there were large-amplitude action potentials, firing in a bursting pattern, in the oviducal nerves. These large action potentials were absent in locusts that had not been egg-laying. These action potentials were associated with both bioelectric potentials and mechanical events in the posterior region of the lateral oviduct and the common oviduct. Electrical stimulation of the oviducal nerve mimicked the effects of spontaneous action potentials, resulting in the appearance of monophasic potentials and contractions. The contractions were graded and dependent upon both frequency and duration of stimulation. It is concluded that the oviducts of Locusta are both myogenic and neurogenic. The role of these contractions in oviposition is discussed.     

Functional anatomy of the female reproductive systems of two spider crabs (Decapoda,Majoidea)

To better understand the mating systems of majoid crabs, we studied the functional anatomy of the female reproductive systems of the spider crabs Leurocyclus tuberculosus and Libinia spinosa, comparing them with those of other Majoidea. Adult females were measured and dissected, and their reproductive systems described macroscopically and histologically. In females of both species, the seminal receptacles are paired globular structures of ecto‐mesodermal origin. The mesoderm‐derived region is lined by a stratified epithelium. The anchoring, proliferative, and secretory strata are clearly recognizable . The ectoderm‐derived region is lined by a simple cylindrical epithelium underlying a cuticle that increases in thickness toward the vagina. The transition between the ectoderm and mesoderm‐derived regions is abrupt, with differences between the studied species: Li. spinosa has a “velum,” whereas Le. tuberculosus presents prominent “folds.” In both species, the position in which the oviduct is connected to the seminal receptacles is intermediate between the dorsal and ventral types previously described in other eubrachyurans. The seminal receptacles of the studied species show four different conditions, which can be distinguished macroscopically based on their shape and amount of sperm stored. We compare our data with those from other Majoidea in an attempt to determine whether the morphology of the seminal receptacles is related to different mating strategies or behaviors.     

Cyclic histological changes of the oviductal-cloacal junction in the viviparous snake Toluca lineata

The structure and seasonal changes of the oviductal-cloacal junction remain poorly understood in most squamates. This study was undertaken to describe the histology of the oviductal-cloaca junction of a female viviparous snake Toluca lineata, during gestation, previtellogenesis, and vitellogenesis. The oviductal-cloacal junction exhibits a wider lumen and thicker layers of connective tissue, smooth muscle layers, and total wall width compared to the posterior vagina. The lining is characterized by thick, short longitudinal mucosal folds. The luminal epithelia differ morphologically from anterior to posterior portions of the oviductal-cloacal junction. The anterior portion is lined with a simple columnar epithelium composed of nonciliated cells. The middle portion is lined with stratified epithelium that contains an apical columnar cell layer that undergoes morphological changes coincident with the reproductive cycle. The posterior portion is lined with a stratified squamous epithelium. The connective tissue underlying the epithelium contains numerous ovoid cells having abundant acidophilic cytoplasmic granules—eosinophils. Copulation occurs during the previtellogenic stage, as evidenced by the presence of abundant spermatozoa in the lumen of the anterior portion and of a copulatory plug in the middle and posterior portion of the oviductal-cloacal junction. J. Morphol. 237:91–100, 1998. © 1998 Wiley-Liss, Inc.     

The oviduct of the ostrichStruthio camelus massaicus

Summary The histology and ultrastructure of the oviduct of three ostriches are described. The ostriches were obtained at the stage just before oviposition. The oviduct wall consists of a mucous membrane carrying mucosal folds showing side branching. The pseudostratified columnar or tall simple columnar epithelium covering the lumen contains ciliated and non-ciliated cells. The ultrastructure of the two cell types and the glandular cells of the lamina propria is described. The vagina has no glands in the subepithelial connective tissue. Beyond the connective tissue, the oviduct wall has two layers of smooth musculature. The inner layer consists of circularly disposed fibres some of which continue into the subepithelial connective tissue to ultimately enter the core of the mucosal folds. The outer layer contains oblique and longitudinally arranged fibres and is peripherally bound by a serous covering.

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Über den Eileiter vonStruthio camelus massaicus

Zusammenfassung Histologie und Ultrastruktur des Eileiters des Straußes werden anhand von drei Individuen beschrieben, die gerade vor der Eiablage geschossen wurden. Der Eileiter ist von einer Schleimhaut ausgekleidet, die in Falten mit Verzweigungen geworfen ist. Das mehrreihige oder einschichtige Zylinderepithel enthält sowohl mit Zilien versehene als auch zilienlose Zellen. Ihre Ultrastruktur und die der Drüsenzellen der Lamina propria werden dargestellt. Die Propria der Vagina enthält keine Drüsen. Peripher vom Bindegewebe der Lamina propria wird die Eileiterwandung durch zwei Lagen glatter Muskulatur vervollständigt. Die innere Schicht besteht aus circulär angeordneten Fasern, von denen einige in das subepitheliale Bindegewebe der Schleimhautfalten einstrahlen. Die äußere Muskelschicht enthält longitudinal und schräg verlaufende Fasern und ist außen von einer Serosa bedeckt.

     

Histomorphometric study of the lower urogenital tract in pre- and post-menopausal women

In this study 22 histomorphometric parameters were used to quantify the histologic changes in the vagina, trigone of the bladder, and the proximal and distal urethra of 37 women aged between 18 and 82 years. The results of this quantitative study revealed a hormonally induced, age-independent atrophy of smooth muscle in the lamina propria of the mucosa and the longitudinal part of the muscular layer in the aforementioned anatomical sites in post-menopausal women. In the lamina propria of the mucosa of the lower urogenital tract in post-menopausal women hormonally induced quantitative changes of blood vessels were not observed. Senile atrophy of smooth muscles was only observed in the deeper part of the muscular layer of the vagina and the trigone of the urinary bladder and was less prominent than the hormonally induced smooth muscle atrophy.     

Molecular phylogenetic and dating analyses using mitochondrial DNA sequences of eyelid geckos (Squamata: Eublepharidae)

Mitochondrial DNA sequences of approximately 2.3 kbp including the complete NADH dehydrogenase subunit 2 gene and its flanking genes, as well as parts of 12S and 16S rRNA genes were determined from major species of the eyelid gecko family Eublepharidae sensu [Kluge, A.G. 1987. Cladistic relationships in the Gekkonoidea (Squamata, Sauria). Misc. Publ. Mus. Zool. Univ. Michigan 173, 1-54.]. In contrast to previous morphological studies, phylogenetic analyses based on these sequences supported that Eublepharidae and Gekkonidae form a sister group with Pygopodidae, raising the possibility of homoplasious character change in some key features of geckos, such as reduction of movable eyelids and innovation of climbing toe pads. The phylogenetic analyses also provided a well-resolved tree for relationships between the eublepharid species. The Bayesian estimation of divergence times without assuming the molecular clock suggested the Jurassic divergence of Eublepharidae from Gekkonidae and radiations of most eublepharid genera around the Cretaceous. These dating results appeared to be robust against some conditional changes for time estimation, such as gene regions used, taxon representation, and data partitioning. Taken together with geological evidence, these results support the vicariant divergence of Eublepharidae and Gekkonidae by the breakup of Pangea into Laurasia and Gondwanaland, and recent dispersal of two African eublepharid genera from Eurasia to Africa after these landmasses were connected in the Early Miocene.     

Phylogenetic relationships among gekkotan lizards inferred from C-mos nuclear DNA sequences and a new classification of the Gekkota

A phylogeny of gekkotan lizards was derived from C- mos nuclear DNA sequence data. Forty-one currently recognized genera, representing all major gekkotan lineages, were included in the study. A total of 378 bp of partial C- mos gene sequences was obtained and aligned. Maximum parsimony (MP) and maximum likelihood (ML) trees were generated based on unweighted analysis using P AUP *; similar tree topologies were recovered by both methods. The Eublepharidae were monophyletic and its relationship to other major clades was poorly resolved. The Pygopodidae of Kluge (1987) was monophyletic, but relationships within this group differed from those retrieved by previous analyses. The Diplodactylini + padded carphodactylines were the sister group of pygopods + padless carphodactylines. The Gekkonidae were monophyletic, but we found no evidence in support of the Teratoscincinae, as Teratoscincus was embedded well within the gekkonids. Both MP and ML analyses supported the basal position of Sphaerodactylus within the gekkonids, in contrast to morphologically based hypotheses. We propose a new higher order classification of the Gekkota that reflect these results. Five gekkotan families: Eublepharidae, Gekkonidae, Pygopodidae, Diplodactylidae, and Carphodactylidae are recognized. The higher order status of the sphaerodactyls will require more intensive sampling of this group. Our results support the hypothesis that the early cladogenesis of the Gekkota was associated with the split of Eastern Gondwanaland from Western Gondwanaland. Divergences among living genera in the Eublepharidae and the Eastern Gondwanan lineages (Diplodactylidae, Pygopodidae and Carphodactylidae) may be older than those in the Gekkonidae.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 353–368.     

Scanning electron microscopic study of intestinal mucosa of the Nile crocodile (Crocodylus niloticus)

As part of an ongoing study of the intestinal tract of the Nile crocodile Crocodylus niloticus, the appearance of the small intestinal mucosa was examined using a scanning electron microscope (SEM). The duodenum displayed ridge-like and complex primary folds, both of which were arranged in a longitudinally directed zigzag pattern. The two types of folds alternated with each other, with the second type following the zigzag contours of the first. The folds were covered with polygonal- and dome-shaped epithelial cells. The latter cell type was less common and was restricted in location to the proximal two thirds of the mucosal folds. Both types of epithelial cells were covered with stubby microvilli which displayed a distinct linear arrangement. Goblet cells were present between the absorptive cells. In the jejunum the basic pattern of the folds persisted except that both types of primary folds became tall and leaf-like. The angle of the zigzag pattern was less acute than in the duodenum. In the ileum the two types of alternating folds decreased in height and were arranged in a longitudinally directed wave-like fashion. The zigzag mucosal folds of the small intestine ended abruptly at the ileorectal junction. The rectum displayed low, irregular folds which formed occasional large, puckered, rosette-shaped structures. The particular arrangement of the intestinal folds fulfills the dual function of promoting the absorptive process and facilitating the smooth passage of the intestinal contents. © 1995 Wiley-Liss, Inc.     

Postnatal development of excitatory innervations in longitudinal smooth muscle of the chicken anterior mesenteric artery

AimsThe anterior mesenteric artery of chickens contains a well-developed outer longitudinal smooth muscle layer in addition to an inner circular layer. Cholinergic and purinergic neurons play crucial roles in excitatory transmission at the longitudinal smooth muscle. The aim of this study was to clarify postnatal development of excitatory neurotransmission of the longitudinal smooth muscle.Main methodsMembrane potentials of smooth muscle were recorded with a microelectrode technique. Perivascular nerves were stimulated by applying electrical field stimulation (EFS).Key findingsHistological examination showed that longitudinal smooth muscles exist in the artery at birth. EFS failed to evoke membrane response in 1-day-old chickens, though it caused depolarization (excitatory junction potential; EJP) in 12-week-old chickens. However, exogenous application of acetylcholine (ACh) or ATP produced depolarization in longitudinal smooth muscle of 1-day-old chickens, suggesting that responsiveness of smooth muscle to excitatory neurotransmitters is already established at birth. In preparations isolated from 10-day-old chickens, EFS caused EJP, which was totally blocked by atropine but not by a non-specific purinoceptor antagonist, suramin. Several purinoceptor subtypes including P2Y1, which may be related to depolarizing response in smooth muscle of adult chickens, were expressed in the anterior mesenteric artery of 10-day-old chickens.SignificanceExcitatory innervation in longitudinal smooth muscle of the chicken anterior mesenteric artery is not established at birth but develops during the early postnatal period. Moreover, development of cholinergic excitatory innervation precedes that of purinergic excitatory innervation, although receptors that mediate purinergic control are already expressed in smooth muscle.     

The fine structure of smooth muscle cells and their relationship to connective tissue in the rabbit portal vein

Summary The smooth muscle of rabbit portal vein was studied by electron microscopy with particular emphasis on the mechanical linkage between the muscle cells and on the distribution of connective tissue.The media of this vein is composed of inner circular and outer longitudinal muscle layers which are orientated almost perpendicularly to each other. The muscle of the inner circular layer shows very irregular contours with much branching and anastomosing of the cytoplasmic processes, which often make membrane contacts with neighbouring cells to form an extensive network of cytoplasmic processes. The muscle cells of the outer longitudinal layer are arranged in densely packed bundles and are spindle-shaped, with no branching processes. Opposing dense areas from neighbouring cells, with variable gap distances (30–100 nm) and close membrane contacts (intermediate junctions) with a gap of 11 nm were observed in both circular and longitudinal muscle layers.In the terminal regions of muscle cells in both circular and longitudinal layers a specialized anchoring structure was present which was closely related to extracellular elastic tissue. Muscle cells in the longitudinal layer showed the most elaborate structure, the tapering end of the muscle cell showing a honeycomb-like structure penetrated by columns of connective tissue compounds. The functional implications of these structures are discussed.     

A comparative anatomical study of the mammalian uterotubal junction

Among eight species of mammals in this study (cattle, sheep, pig-tail and rhesus monkeys, rabbit, pig, rat, and dog) four basic patterns of anatomical structure at the uterotubal junction are described. The classification of types is based upon the presence or absence of an intramural portion of the oviduct and of isthmal folds or plicae projecting into the lumen of the uterine cornu. Histological variations are reported for three tissues: epithelial and connective of the mucosa and smooth muscle of the tunica muscularis. In the epithelium during the estrous cycle the differences recorded include: (a) absence of ciliated cells in the distal end of the oviduct in rat and dog; (b) variations in ciliated and nonciliated cells in (1) cell height, (2) location, shape and stainability of the nucleus, and (3) in amount and stainability of apical cytoplasm; (c) presence of lymphoblast-like cells which appear to migrate through the epithelium from the lamina propria. The connective tissue of the mucosa, as a circular layer and as cores for the mucosal folds, shows variations in thickness and in relative density of cells and fibers of the matrix. Emphasis is given to the presence of an inner longitudinal layer of smooth muscle in the tunica muscularis of the distal oviduct in six of the eight species.     

Ultrastructure of the neuromuscular system of the polyp of Aurelia aurita L., 1758 (Cnidaria,scyphozoa)

Fine structural study indicates that the neuromuscular system of stage I polyps of Aurelia aurita is exclusively ectodermal. The three major muscle fields are the radial muscles of the oral disc, the longitudinal muscles of the tentacles, and the muscle cords of the septae and the column; the muscle fields are in physical continuity at the peristomial pits and share a common innervation and type of myofibril. The myofibril is striated in the tentacle base, in the outer oral disc, and in the upper part of the muscle cord; it grades into a smooth muscle toward the tentacle tip, the mouth, and the lower part of the cord. There is a fourth field of longitudinal smooth muscle in the pharynx. The nervous system consists of an epithelial sensory cell in the tentacle and a single type of neuron found in the subepithelial layer of the tentacle, oral disc, and muscle cord. The lack of gap junctions suggests that there is no nonnervous conduction system. The subepithelial layer also contains three types of fibers and a type of soma which cannot be characterized as neuronal. The soma is identified as the “neurosecretory cell” described in Chrysaora. The absence of neuromuscular elements in the column and stolon distinguishes the Aurelia aurita collected from Washington, USA, from English polyps previously described.     

Morphology and ultrastructure of the anterior end of Diplocirrus longisetosus Marenzeller, 1890 (Flabelligeridae, Polychaeta, Annelida)

The morphology and ultrastructure of the sedentary polychaete Diplocirrus longisetosus Marenzeller, 1890, collected from the White Sea, were studied using dissection, histological methods, light microscopy, and both scanning and transmission electron microscopy. The prostomium and peristomium carry a pair of palps, eight branchiae, a pair of nuchal organs and two nephridiopores, ciliated folds and the mouth. The prostomium, peristomium and the first chaetigerous segment with all appendages comprise the so-called siphon complex. The mouth leads to a pharyngeal organ that is closed ventrally and composed of a ventral muscle bulb adjoined dorsally by two folds projecting into the pharyngeal lumen. These parts are connected and enveloped by the longitudinal investing muscle. No tongue-like organ is present. The nervous system of the siphonal part comprises the brain, the circum-oesophageal connectives and the ganglia of the peristomium and first chaetigerous segment.     

Functional morphology of the female reproductive system of a crab with highly extensible seminal receptacles and extreme sperm storage capacity

We studied the functional morphology of the female reproductive system of the purple stone crab Danielethus crenulatus . The most remarkable feature is the relative storage capacity and extensibility of the seminal receptacles. These receptacles are a pair of simple sacs that lack internal structures dividing the internal lumen. Differences in seminal receptacle size and contents are accompanied by conspicuous changes in receptacle lining at a tissue level. Full seminal receptacles contain discrete sperm masses formed by hardened fluid and densely packed spermatophores. Different sperm masses are likely from different mates and their stratified disposition within the seminal receptacles is compatible with rival sperm displacement and last sperm precedence. Additionally, the anatomical structure of the vulva and vagina suggest active female control over copula. We discuss our results in the general context of sperm storage in brachyurans and the implications for the mating system of this species.     

The female genital system of Ooperipatellus decoratus (Onychophora, Peripatopsidae): an ultrastructural study

The female genital system of the oviparous peripatopsid Ooperipatellus decoratus consists of an ovary, oviducts equipped with receptacula seminis and additional pouches, uteri, and a vagina. It is examined using transmission and scanning electron microscopy. The ovary is made up of paired ovarian tubes united anteriorly and posteriorly and differentiated into a sterile dorsal part and a fertile ventral part with exogenous oocytes. Fertilization presumably occurs in the oviducts once the oocytes pass the receptaculum seminis. Although the receptacula seminis have been reported to occur in juvenile O. decoratus females only, the present study reveals that they are present in adult females as well. Their wall consists of a cuboidal epithelium covered with a thin collagen-muscle layer. The additional pouches are projections of the oviducts facing the receptacula seminis. They are distally closed to the haemocoel by a flattened epithelium and lack external muscle cells. A thin collagen layer is only found proximally. The uteri are characterized by a columnar epithelium with folded cell membranes allowing extension of the uteri, thus facilitating the passage of the large uterine eggs towards the vagina. Another dominating feature of the uteri is a distally increasing secretory production, which probably contributes to chorion development. Cilia occurring along the entire length of the uteri are considered to assist in the transport of eggs towards the vagina.     

Paradorippe granulata – A crab with external fertilization and a novel type of sperm storage organ challenges prevalent ideas on the evolution of reproduction in Eubrachyura (Crustacea: Brachyura: Dorippidae)

Two fundamentally different sperm storage organs occur in Brachyura. The probably paraphyletic podotremes show intersegmental spermathecae, which are distant from oviducts and coxal gonopores. Hence, fertilization is external. In contrast to this, the seminal receptacles of Eubrachyura are directly connected with the ovaries. Thus, at least initial fertilization is internal. This pattern has been interpreted as an apomorphy of Eubrachyura. To test this hypothesis, we studied the morphology of the reproductive organs of Paradorippe granulata, a representative of the putatively early diverging eubrachyuran lineage Dorippoidea. Applying histology, 3D-reconstructions and micro-computed-tomography we revealed a novel type of sperm storage organ. Female P.granulata lack the characteristic eubrachyuran seminal receptacle. Instead sperm is stored in four cuticle-lined bursae, two on each side of the paired oviducts. The elaborate bulbous male gonopod with several terminal processes is adapted to transferring sperm into the female twin bursae. Since oviducts and twin bursae are not directly connected, spermatozoa and oocytes mix when gametes pass through the sternal vulva. Thus, fertilization in P.granulata is external. Our finding of a eubrachyuran crab that lacks seminal receptacles and exhibits external fertilization calls prevailing concepts on the evolution of sperm storage in Eubrachyura into question.     

Histological studies of the dorsal nasal,Angularis Oculi,and facial veins of sheep (Ovis aries)

Selective brain cooling (SBC) requires vasoactivity in the superficial veins of the face of the animal. This vasoactivity is possible because of an adequate amount of smooth muscle in the tunica media of each of these superficial vessels, enabling it to act as a “muscle sphincter.” In this study, the angularis oculi, dorsal nasal, distal, and proximal parts of the facial veins in sheep were examined histologically to describe an anatomical basis for SBC. Measurements of the tunica media thickness, the lumen diameter, and the ratio of these measurements showed that the relative tunica media thicknesses in the angularis oculi vein and the dorsal nasal vein are statistically smaller (P < 0.001) than in the distal or the proximal parts of the facial vein. In the angularis oculi, dorsal nasal, and distal part of the facial vein, the tunicae mediae were composed of five to seven circularly arranged smooth muscle layers, suggesting their ability to vasoconstrict. The proximal part of the facial vein possesses both circularly and longitudinally arranged smooth muscle layers. The circular smooth muscle layers suggest a vasoconstrictory function, whereas the longitudinal smooth muscle layers imply a vasodilatory function in this part of the facial vein. Both the dorsal nasal and the proximal part of the facial vein, but not the angularis oculi or the distal part of the facial vein, possess endothelial valves near their confluences with other veins. It was concluded from this study that the angularis oculi and the distal part of the facial vein vasoconstrict, whereas the proximal part of the facial vein vasodilates, enabling the necessary changes in blood flow in SBC. J. Morphol. 237:275–281, 1998. © 1998 Wiley-Liss, Inc.