Showing papers in "Journal of Morphology in 1997"

Description of the adult skeleton and developmental osteology of the hyperossified horned frog, Ceratophrys cornuta (Anura: Leptodactylidae)

Abstract: The adult skeleton and tadpole chondrocranium of the leptodactylid frog, Ceratophrys cornuta (Ceratophryinae), are described in detail, including the ontogenetic development of the chondrocranium and the ossification sequence of the skeleton. The chondrocranium of the carnivorous larvae is unique in lacking a frontoparietal fontanelle and possessing a complete dorsal roof of cartilage. Furthermore, the chondrocranium is extremely robust, particularly those elements involved in the feeding mechanism; these include large palatoquadrate cartilages, stout Meckel's, supra-, and infrarostral cartilages, and short, wide, cornua trabeculae. The chondrocranium of C. cornuta resembles that described for Ceratophrys cranwelli, but differs from the chondrocrania reported for the species of Lepidobatrachus. The large adult skull is hyperossified; most elements are fused into a single unit, and nearly all dermal elements are ornamented, casqued, and co-ossified. Calcification is present in nearly every cartilaginous element of the skeleton in larger (older) adults. Several osteological characters previously used in ceratophryine systematics, such as the otic ramus of the squamosal and the columella, are reassessed. Contrary to previous reports, the ossified, dorsal dermal shield above the vertebral column in many ceratophryine anurans is absent in C. cornuta. With few exceptions, the ossification sequence relative to metamorphosis is consistent with those that are known for other anurans. The squamosal arises from three distinct centers of ossification, including an otic element. The frontoparietal arises from two centers of ossification that fuse early in development. A robust postorbital arch is formed primarily by the otic flange of the frontoparietal, which articulates laterally with the medial border of the otic ramus of the squamosal. Changes in the timing of development, or heterochrony, are involved with the evolution of the unusual skull and skeleton of ceratophryine frogs.

Kinematics and Functional Morphology of Aquatic Feeding in Australian Snake-Necked Turtles (Pleurodira; Chelodina)

Abstract: Head kinematics during aquatic feeding of the Australian long-necked turtle (Chelodina) were studied by means of high speed video recordings. Buccal expansion was assessed by calculation of elliptical cross-sectional surfaces. Further, displacements of head, carapace, and prey in the earth bound frame, of the prey relative to the center of the gape, and of the head relative to the carapace were determined. Rates of change (velocities) of all these variables were calculated. These data are combined with information on the osteology and myology of the head. The robust development of the large hyobranchial apparatus, the massive intercornuatus muscle, and the presence of the branchiosquamosus muscle were related to aquatic feeding skills. Head kinematics are variable in amplitude and relative timing, but proceed always in a rostrocaudal sequence. According to their effect on the prey, two components are distinguished in the process of expansion. The first compensates for head/body movements (compensatory suction). The second causes distinct acceleration of water and prey (inertial suction). The latter component is mainly driven by the abduction of the second branchial arch. In spite of largely different structural solutions, optimal feeding conditions as deduced for suction in feeding fishes are also employed by Chelodina. This further promotes the assumption that hydrodynamics constrain evolutive solutions for aquatic feeding.

Osteology and skeletal development of Discoglossus sardus (Anura: Discoglossidae)

Abstract: Although frogs in the archaeobatrachian family Discoglossidae are reasonably well known, descriptions of their larval skeletons and osteogenesis are almost nonexistent. Skeletogenesis, chondrocranial development, and the adult skeleton of Discoglossus sardus are described on the basis of cleared and stained, dry, and radiographed specimens. In D. sardus, the first elements to ossify are the parasphenoid, frontoparietals, exoccipitals, neural arches, ischium, long bones, and dermal elements of the pectoral girdle (Gosner Stage 36). Major reconstruction of the chondrocranium begins at the onset of metamorphosis (Stage 41), contemporaneous with the ossification of the premaxillae, maxillae, vomers, and septomaxillae. Several cranial (e.g., pterygoid, mentomeckelian, sphenethmoid) and postcranial (e.g., carpals, hyoid) elements do not commence ossification until after metamorphosis (Stage 46). Discoglossids are characterized by the presence of a facial foramen in the lateral wall of the chondrocranium, a rod-like epipubis developing from two primordia, and the lack of a neopalatine bone. Adult male Discoglossus possess an enlarged, crested metacarpal II and a broad prepollical element. This detailed description serves as a model to compare the development of other discoglossid frogs and provides detailed descriptions of several enigmatic structures. J. Morphol. 233:267–286, 1997. © 1997 Wiley-Liss, Inc.

Allometric patterning in the limb skeleton of bats: Implications for the mechanics and energetics of powered flight

Abstract: Allometric analysis was employed to compare linear dimensions of forelimb and hindlimb bones (humeri, radii, third and fifth metacarpals, third and fifth manual phalanges, femora, and tibiae) of 227 species of bats and 105 species of nonvolant mammals of varying degrees of phylogenetic affinity to bats After accounting for body size, all forelimb bones are longer in bats than in nonvolant species, with the exception of humeri and radii of a few highly arboreal primates Hindlimb bones are generally, but not uniformly, shorter in bats than in other mammals For the humerus, radius, and metacarpals, midshaft diameters are greater in bats than in their comparably sized relatives Proximal phalangeal midshaft diameters are statistically indistinguishable from those of other mammals, and distal phalanges show significantly reduced outer diameters The pattern of relative reduction in wing bone diameters along the wing's proximodistal axis parallels the reduction in bone mineralization along the same axis, and a similar pattern of change in cortical thickness from the smallest wall thicknesses among mammals in the humerus and radius to the greatest wall thicknesses among mammals in the phalanges The combination of altered cross-sectional geometry and mineralization appears significantly to reduce the mass moment of inertia of the bat wing relative to a theoretical condition in which elongated bones preserve primitive mammalian mineralization levels and patterns of scaling of long bone diameters This intercorrelated suite of skeletal specializations may significantly reduce the inertial power of flight, contributing significant energetic savings to the total energy budgets of the only flying mammals J Morphol 234: 277-294, 1997 © 1997 Wiley-Liss, Inc

An electromyographic analysis of hindlimb function in Alligator during terrestrial locomotion.

Abstract: The neuromuscular control of the hindlimb of American alligators (Alligator mississippiensis) walking on a treadmill was analyzed using simultaneous electromyography (EMG) and cineradiography. EMG and kinematic data were integrated with myological information to discern the interplay of muscles mediating hip and knee movement during the high walk. Twelve muscles, subdivided into 23 individual heads, cross the hip joint of Alligator. Activity patterns of 12 heads of 11 hip muscles and one knee muscle were recorded and quantified. An additional five heads from four muscles were recorded in single individuals. During the stance phase, the caudofemoralis longus prevents hip flexion and actively shortens to retract the femur through an arc of 60-80°. At the same time, the adductor femoris 1 and pubo-ischio-tibialis control femoral abduction. The knee is extended 30-40° during stance by contraction of the femoro-tibialis internus. These stance phase muscles often produce discontinuous, periodic EMG signals within their normal burst profile. In late stance and early swing, the ilio-fibularis and the pubo-ischio-tibialis are responsible for flexing the knee. The limb is protracted by the pubo-ischio-femoralis internus 2 and pubo-ischio-femoralis externus 2, which flex the hip. The ilio-femoralis abducts the limb during swing to suspend it above the tread. The role of the ambiens 1, which is active in midswing, is unclear. The ilio-tibialis 2, flexor-tibialis externus and flexor-tibialis internus 2 yield sporadic, low amplitude EMGs; these muscles are recruited at a very low level, if at all, during the slow high walk. Although EMGs do not conclusively delineate muscle function, activity patterns are particularly helpful in elucidating the complex interaction of muscular heads in this system. J. Morphol. 234:197-212, 1997. © 1997 Wiley-Liss, Inc.

Comparative functional morphology of mandibular forward movement during mastication of two murid rodents, Apodemus speciosus (Murinae) and Clethrionomys rufocanus (Arvicolinae)

Abstract: The anatomy of the masticatory apparatus, the direction in which masticatory muscles act during mastication, and jaw muscle forces as estimated by muscle dry weight are compared between two murid rodents, the Japanese field mouse (Apodemus speciosus, subfamily Murinae) and the gray red-backed vole (Clethrionomys rufocanus; subfamily Arvicolinae). The occlusal forces exerted by the deep masseter and the anterior temporalis are large in C. rufocanus. Furthermore, in this species, the angle between the sagittal plane and the occlusal plane of the cheek teeth is larger than in A. speciosus. Therefore, a relatively large occlusal force can be generated in C. rufocanus. The estimated line of action of the anterior temporalis differs markedly between these two species. The functional significance of this difference is discussed relative to the adaptive dental characteristics for food processing, the forces required to masticate different types of food, and the forces that control mandibular forward movement.

Comparative ontogenetic shape changes in the skull of Caiman species (Crocodylia, Alligatoridae).

Abstract: Ontogenetic shape changes in the skull of three species of the genus Caiman (C. latirostris, C. sclerops, and C. yacare) are compared by geometric morphometrics for three-dimensional configurations (the least-squares analysis). The technique for obtaining the landmark coordinates is a simplification of the algorithm for multidimensional scaling. The ontogenetic nonlinear shape changes are similar in the three species but occur in a lesser extent in C. latirostris. These seem to be correlated with functional changes in the skull. The uniform shape change corresponds to an elongation of the skull, dorsoventral flattening, and lateral compression in C. sclerops and C. yacare. There is some lateral broadening in C. latirostris. Differences in the ontogenetic processes probably cause the differences in diet observed between C. latirostris and the other two species. Neotenic evolution seems to have acted in the skull of C. latirostris, and a posterior amplification of the early divergence led to a repatterning of the shape ontogenetic trajectory in this species. J. Morphol. 231:53–62, 1997. © 1997 Wiley-Liss, Inc.

Comparative myology of the forelimb of squirrels (Sciuridae).

Abstract: The musculature of the shoulder, arm, and forearm was studied in 19 genera of squirrels, representing the Pteromyinae (flying squirrels) and all 7 tribes of the Sciurinae (tree and ground squirrels). The objective was to locate derived anatomical features of functional or phylogenetic significance and to determine how much morphological variation underlies the diverse locomotor behavior of squirrels, which includes terrestrial and arboreal bounding, climbing, digging, and gliding. The fossil evidence suggests that arboreality is primitive for squirrels, and in fact tree squirrels appear to represent the primitive sciurid morphology. Ground squirrels are less uniform and exhibit a few derived features, including a clavobrachialis muscle not seen in other squirrels. Pygmy tree squirrels, which have evolved independently in three tribes, exhibit convergence of forelimb anatomy, including the loss or reduction of several muscles in the shoulder and forearm. The forelimb anatomy of flying squirrels is the most derived and differs from that of tree squirrels in details of shoulder, arm, and forearm musculature. Some of these muscular differences among squirrels have phylogenetic significance, being shared by closely related genera, but none has significance above the tribal level. Many of the differences suggest a variety of changes in function that are amenable to further study.

Morphogenesis of placental membranes in the viviparous, placentotrophic lizard Chalcides chalcides (Squamata: Scincidae).

Abstract: In the scincid lizard Chalcides chalcides, females ovulate small ova and supply most of the nutrients for development by placental means. The yolk is enveloped precocially by extraembryonic ectoderm and endoderm during the gastrula stage, establishing a simple bilaminar yolk sac placenta. The shell membrane begins to degenerate at this time, resulting in apposition of extraembryonic and maternal tissues. A true chorioplacenta has developed by the early pharyngula stage, as has a choriovitelline placenta and the first stages of an omphaloplacenta. Although the choriovitelline membrane disappears rapidly, the omphaloplacenta spreads to occupy the entire abembryonic pole. The yolk cleft is not confluent with the exocoelom, and no omphalallantoic placenta develops. By the limb-bud stage, an allantoplacenta has been established, with a mesometrial placentome composed of interdigitating ridges of chorioallantois and uterine mucosa. The discovery of five distinct placental arrangements in this species, three of which are transitory and two of which have not previously been recorded in reptiles, emphasizes the need for accounts that specify ontogenetic stages and the precise identity and composition of squamate placental membranes. Contrary to previous interpretations, the pattern of extraembryonic membrane development in C. chalcides is evolutionarily conservative, despite the presence of a reduced yolk mass and cytological specializations for nutrient transfer. Our observations indicate that substantial placentotrophy can evolve in squamates without major modifications of morphogenetic patterns. J Morphol 232:35-55, 1997. © 1997 Wiley-Liss, Inc.

Scaling of the mandible in squirrels.

Abstract: We compared the shape of the mandible among New World tree squirrels and selected outgroup taxa using linear measurements and areas defined by the median axis and conventional anatomical landmarks. We modified the median axis technique to define novel measurements, which proved complementary to those obtained from conventional landmarks. Allometric analyses showed that the scaling of the mandible among the New World tree squirrels is generally isometric (as has been observed in other groups of mamimals), but diverges from isometry in a tendency in smaller animals for the masseteric ridge to be displaced anteriorly, the condylar process and posterior portion of the ascending ramus to be relatively elongated, and the coronoid process to be shortened. Allometric analyses also revealed the ways and extent that outgroup taxa deviated from the scaling pattern observed for the New World tree squirrels. A flying squirrel (subfamily Pteromyinae), a moderate-sized callosciurine squirrel, and three species of pygmy tree squirrels from Asia and Africa show mandibular proportions very similar to those predicted for New World tree squirrels of corresponding size. Ground squirrels (tribe Marmotini) and successively more distant relatives such as Aplodontia, two myomorph rodents, and a rabbit show greater differences from the New World tree squirrels in their mandibular proportions. Combining the use of median-axis and conventional measurements makes it possible to examine changing relationships between locations of anatomically homologous landmarks and the geometry of the form. J Morphol 232:107–132, 1997. © 1997 Wiley-Liss, Inc.

Oviductal structure in a viviparous New Zealand gecko, Hoplodactylus maculatus.

Abstract: Oviductal structure is described in New Zealand's common gecko, Hoplodactylus maculatus, over four reproductive stages (early/mid-vitellogenesis, late vitellogenesis, early pregnancy, late pregnancy), using light, scanning electron, and transmission electron microscopy. Five regions of the oviduct are recognized: infundibulum, uterine tube, isthmus, uterus, and vagina. Up to three cell types make up the luminal epithelium of the oviduct: ciliated, nonciliated, and bleb cells. The function of bleb cells (seen in the infundibulum only) is unknown, but observation of these cells using transmission electron microscopy suggests that they are involved in secretory activity. Mucosal glands in the uterine tube possess large numbers of secretory granules of varying electron densities. Additionally, these glands appear to function as sperm storage tubules. Numerous sperm are seen in the glands during late vitellogenesis and early pregnancy. Very few uterine mucosal (shell) glands are seen during vitellogenesis, which is consistent with the observation that only a fine shell membrane covers the egg during early pregnancy. By late pregnancy, extraembryonic membranes lie adjacent to the uterus allowing the formation of the omphalo- and chorioallantoic placentas. Maximum cell height in the luminal epithelium is seen during vitellogenesis. The maximum percentage of ciliated cells making up the epithelial layer is seen during pregnancy. The low number of uterine mucosal glands seen in H. maculatus is a feature typical of other viviparous reptiles described, despite independent evolutions of viviparity. Although oviductal structure has been described in the literature for various reptiles, several ultrastructural features seen in this study highlight the lack of detailed understanding of this tissue. J. Morphol. 234:51-68, 1997. © 1997 Wiley-Liss, Inc.

Morphological Specializations of the Digestive Tract of Zacryptocerus rohweri (Hymenoptera: Formicidae)

Abstract: Light, scanning, and transmission electron microscopy are used to examine the morphology and ultrastructure of the peculiar digestive tract of the turtle ant, Zacryptocerus rohweri. The proventriculus is heavily sclerotized and covered with clusters of small spines. Narrow spine-lined channels converging at the opening to the midgut act as a fine filter of food; particles .12.5 µm are unable to pass through the proventriculus. In the midgut, ultrastructural study reveals bacteria among the microvilli of midgut epithelial cells. The hindgut of Z. rohweri consists of an enlarged, dark- colored pouch filled with masses of bacteria of three major morphotypes. A thick layer of circular muscle and deep infoldings of the epithelium greatly increase surface area for absorption. Newly emerged individuals appear to acquire these microorganisms by soliciting material from the abdomen tip of other older workers in the colony. Whether or not the hindgut bacteria are true symbionts is unknown; their acquisition and presence suggest that they may supplement the ants' limited, liquid diet by supplying essential amino acids and other nutrients. J. Morphol. 234:253-262, 1997. r 1997 Wiley-Liss, Inc.

Ultrastructural study of spermatogenesis and the spermatozoon in Postorchigenes gymnesicus (Trematoda, Lecithodendriidae).

Abstract: An ultrastructural study of spermatogenesis, spermiogenesis, and spermatozoa in Postorchigenes gymnesicus is presented. Cytoplasmic projections originating in nurse cells surround the spermatogonia, which are located at the periphery of the testes. Primary spermatocytes attached to a cytophore show synaptonemal complexes and a pair of centrioles. Spermiogenesis begins with the appearance of a cytoskeletal structure formed by an intercentriolar body and two perpendicular centrioles. An axoneme and a striated rootlet emerge from each centriole. The progressive rotation and fusion of both flagella with the median process occurs simultaneously with the migration of nucleus to the distal tip of the forming spermatozoon. The mature spermatozoon consists of three regions: (1) the nuclear region, containing the nucleus, one mitochondrion, two 9+1 axonemes, and cortical microtubules; (2) the intermitochondrial region, containing two axonemes; and (3) the mitochondrial region with another mitochondrion, two axonemes, cortical microtubules, and external ornamentation symmetrically and asymmetrically arranged coincidental with the cortical microtubules. Glycogen particles, absent in testicular cells, are abundant in the spermatozoon. Ultrastructural features of the non-nuclear region of the spermatozoon are specific for P. gymnesicus and are proposed to characterize the spermatozoon of digenean species. J. Morphol. 234:223-232, 1997. © 1997 Wiley-Liss, Inc.

Morphology of hemocytes from the freshwater prawn Macrobrachium rosenbergii.

Abstract: Using morphological criteria, we identified three types of blood cells in the freshwater prawn Macrobrachium rosenbergii. Hyaline hemocytes, the most abundant type, have few large cytoplasmic granules, a large nucleocytoplasmic ratio, and lyse spontaneously in the absence of anticoagulant. Granular hemocytes are heterogeneous in size and in density of their granules. They are phagocytic and readily spread on substrates. The third type of hemocytes, identified as undifferentiated hemocytes, are the least abundant. The hemocytes of this economically relevant crustacean are compared with blood cells of other decapods. J. Morphol. 234:147-153, 1997. © 1997 Wiley-Liss, Inc.

Comparative morphology of Western Australian varanid lizards (Squamata: Varanidae)

Abstract: Varanid lizards, which vary considerably in body mass both interspecifically and intraspecifically, are generally considered to be morpho- logically similar. However, significant and non-isometric variation in the relative appendage dimensions for 17 species of Western Australian goannas suggest that these lizards are not morphologically conservative. The first and second canonical variates clearly distinguish the two subgeneral Odatria and Varanus, and species are generally sexually dimorphic. The morphological variation observed among these 17 species of goanna is associated with foraging mode and ecology. However, no single or small group of morphological dimensions discriminates phylogenetic groups, sexes, or ecological groups, and body size is an important component in these analyses. J. Morphol. 233:127-152, 1997. r 1997 Wiley-Liss, Inc. The morphology of a lizard is largely deter- mined by its ancestry, ecological niche, body size, and development (Peters, '83; Calder, '84; Schmidt-Nielsen, '84). In addition, some species of reptile are also sexually dimorphic in body shape or size (Vitt and Cooper, '85; Shine, '92). The lizard family Varanidae pro- vides an excellent opportunity to study the interrelationships of body size and shape with ecology. Varanidae consists of only a single extant genus, Varanus, and contains about 45 species. The mass range ofVaranus is more than three orders of magnitude, ranging from <20g(V. brevicauda; personal observations) to <54 kg (V. komodoensis; Auffenberg, '81). There are a variety of eco- logical specializations, including tree climb- ing, rock scampering, and swimming. Never- theless, a numbers of authors (Shine, '86; Greer, '89; King and Green, '93b; Pianka, '95) have suggested that their body form is conservative compared with the variation in other families of lizards. The genus Varanus is considered to be monophyletic (Baverstock et al., '93), and thus comparison of varanid species is not complicated by higher level phylogenetic dif- ferences. Baverstock et al. ('93) summarized the phylogeny ofVaranusand suggested four clades based on immunogenetic and karyo- typic studies: an Asian clade, an African clade, anAustralian/S.E.Asian clade of large goannas (subgenus Varanus), and a clade of Australian pygmy goanna (subgenus Odatria). Nearly all of the members of the Varanus clade (except V. komodoensis and V. salvadorii) and all of the members of the Odatria clade are found in Australia; V. er- emiusprobably belongs to theOdatriagroup, although it was initially placed outside these clades (Pianka, '95). Morphometric examina- tion of the 18 species/subspecies of goanna found in WesternAustralia allows a compari- son of theVaranusandOdatriasubgenera. Others (e.g., Snyder, '54; Collette, '61; Ball- inger, '73; Laerm, '74; Moermond, '79; Pianka, '86; Losos, '90a-c; Miles, '94) have suggested that there are morphological char- acteristics that can be associated with habi- tat and performance traits. Pianka ('68, '69, '70a,b, '71, '82, '86, '94) provides most of the limited ecological and behavioral data, and some additional general information on their ecology is provided by Storr et al. ('83) and Wilson and Knowles ('92). Greer ('89) groups all Australian goannas into four broad eco- logical categories (ground, rocky outcrop, ar- boreal, and aquatic/arboreal). The only obvi-

Fine structure of dicyemid mesozoans, with special reference to cell junctions.

Abstract: The fine structure of the dicyemid mesozoan, Dicyema acuticephalum, from Octopus vulgaris, was studied with special attention to intercellular junctional complexes between various kinds of cells. Two types of intercellular junction, namely, adherens junctions and gap junctions, were found in both vermiform stages and in infusoriform embryos. Adherens junctions were classified into two types. Zonulae adherentes-like junctions were observed between adjacent peripheral cells at vermiform stages, between adjacent external cells of infusoriform embryos, and between members of groups of internal cells that covered the urn in infusoriform embryos. Maculae adherentes-like junctions were seen between a peripheral cell and an axial cell at vermiform stages. In infusoriform embryos, these junctions were observed between various types of cells, excluding urn cells. Gap junctions were found between adjacent peripheral cells at vermiform stages, whereas in infusoriform embryos these junctions were located between various types of cells excluding urn cells. Dicyemids might be the most primitive multicellular animals to possess these basic types of cell junctions. Ciliary rootlet systems at vermiform stages and in infusoriform embryos were unique in structure compared with those of other primitive multicellular animals. J Morphol 231:297-305, 1997. © 1997 Wiley-Liss, Inc.

Development and early differentiation of gonad in the european eel (Anguilla anguilla [L.], Anguilliformes, Teleostei): A cytological and ultrastructural study.

Abstract: The structure of the gonad of the European eel (Anguilla anguilla [L.]), an "undifferentiated" gonochoristic teleost, was investigated by transmission electron microscopy from 6-8 cm elvers to 22 cm yellow eels with juvenile hermaphroditic gonads. The pear-shaped gonads of 6-8 cm elvers assume, in 12-15 cm eels, a lamellar shape and enlarge by migration of germ cells, which we refer to as primary primordial germ cells. In the gonads of ∼ 16 cm eels, the primary primordial germ cells multiply, giving rise to clusters of germ cells that have ultrastructural characteristics of the primary primordial germ cells but show giant mitochondria, enlarged Golgi complexes, and round bodies not limited by membranes. We refer to these as secondary primordial germ cells. In 16-18 cm eels, syncytial clones of oogonia interconnected by cytoplasmic bridges are also observed. In 18-22-cm-long eels, the gonads contain primordial germ cells, oogonial clones, early oocyte cysts, single oocytes in early growth stages, and primary spermatogonia. Such germ cells are present in the same cross section where they are either intermingled or are in areas of predominantly female germ cells close to areas with predominantly male germ cells. These gonads are juvenile hermaphroditic and should be considered ambisexual because in larger eels they differentiate either into an ovary or into a testis. Somatic cells always envelop the germ cells following their migration into the gonad. These somatic cells first show similar ultrastructural features and then differentiate either into early Sertoli cells investing spermatogonia, or into early follicular (granulosa) cells investing the early previtellogenic oocytes. In eels ∼ 14 cm long, primitive steroid-producing cells also migrate into the gonad. In the ambisexual gonad they differentiate either into immature Leydig cells in the male areas, or into early special cells of the theca in the female areas. Nerve fibers are joined to the steroid-producing cells. Gonad development and differentiation are also associated with structural changes of the connective tissue characterized by the progressive appearance and deposition of collagen fibrils first in the mesogonadium, then in the gonad vascular region, and then in the germinal region. The collagen-rich areas are massive in the male areas and reduced in the female ones. J. Morphol. 231:195-216, 1997. © 1997 Wiley-Liss, Inc.

The arterial system of the sperm whale (Physeter macrocephalus)

Abstract: The angioarchitecture of the sperm whale is basically similar to that of other mammals, but it has specific attributes associated with the aquatic environment of this animal and its tolerance for deep and long diving. Specialized features include an expansive aortic arch, unusually far anterior localization of the arch, symmetrical branching of common carotid and subclavian arteries from the aorta, the absence of direct connection between internal carotid arteries and brain arteries, the absence of a costocervical artery, and the presence of a well-developed occipital artery. The sperm whale has extraordinarily well-developed retia mirabilia, distributed in the cranial cavity, vertebral canal, neck and thoracic cavity, around the optic nerve, and in the walls of the uterus. These retia are more extensively developed in the sperm whale than in any other cetacean previously studied. J. Morphol. 234:37–50, 1997. © 1997 Wiley-Liss, Inc.

Evidence for participation of the epidermis in the deposition of superficial layer of scales in zebrafish (Danio rerio): A SEM and TEM study.

Abstract: Comparative studies on scale structure and development in bony fish have led to the hypothesis that elasmoid scales in teleosts could be dental in origin. The present work was undertaken to determine whether the scales in zebrafish (Danio rerio), a species widely used in genetics and developmental biology, would be an appropriate focus for further studies devoted to the immunodetection of dental components or to the detection of the expression of genes coding for various dental proteins in fish scales. The superficial region of mature and experimentally regenerated scales and its relationships to the epidermal cover were studied in adult zebrafish using scanning (SEM) and transmission (TEM) electron microscopy. The elasmoid scales are relatively large, thin, and are located in the upper region of the dermis, close to the epidermis. In adults, the surface of the posterior region appears smooth at the SEM level and is entirely covered by the epidermis. During regeneration, the relationship of the epidermal cover to the scale surface is established within 4 days. This interface is easier to study in regenerating than in mature scales because the former are poorly mineralized. TEM revealed that: (1) the epidermis is in direct contact with the scale surface, from which it is separated only by a basement membrane-like structure, (2) there are no dermal elements at the scale surface except at the level of grooves issuing from the focus and crossing the scale surface radially, (3) the mineral crystals located in this superficial region are perpendicular to the scale surface, whereas those located deeper within the collagenous scale matrix are randomly disposed, and (4) when decalcified, the matrix of the superficial region of the scale appears devoid of collagen fibrils but contains thin electron-dense granules, some of which are arranged into layers. The continuous epidermal covering, the absence of dermal elements, as well as the fine structure of the matrix and its type of mineralization, strongly suggest that epidermal products, possibly enamel-like proteins, are deposited at the scale surface and contribute to the thickening of the upper layer in zebrafish scales. J. Morphol. 231:161-174, 1997. © 1997 Wiley-Liss, Inc.

Hypochord, an enigmatic embryonic structure: study of the axolotl embryo.

Abstract: The hypochord of the axolotl embryo is first visible at an early tailbud stage, forming a rod-like structure, situated immediately under the notochord. A profusion of extracellular matrix fibrils is attached to the dorsolateral regions of the hypochord, linking it with the somites. A basal lamina develops around the hypochord, indicating an epithelial type of cell differentiation. Abundant rough endoplasmic reticula in the hypochord cells suggest lively synthetic activity. Prospective endoderm cells were vitally labeled with the lipophilic dye 1,1-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine perchlorate (DiD) at the gastrula stage. Cells labeled with the dye were later found in the hypochord as well as in the gut endoderm. This shows that the hypochord is of endodermal origin, contrary to recent suggestions that the hypochord is of mesodermal origin, but consistent with histological data. After about 8 days of existence, the hypochord disappears. Experimental results, using an apoptosis detection kit, indicate that the hypochord cells may disintegrate by a type of apoptotic cell death. The close association between the hypochord and developing dorsal aorta suggests that the hypochord could be involved in the positioning of the dorsal aorta, which forms under it.

Morphological conservation of limb natural pendular period in the domestic dog (Canis familiaris): implications for locomotor energetics.

Abstract: For better understanding of the links between limb morphology and the metabolic cost of locomotion, we have characterized the relationships between limb length and shape and other functionally important variables in the straightened forelimbs and hindlimbs of a sample of 12 domestic dogs (Canis familiaris). Intra-animal comparisons show that forelimbs and hind- limbs are very similar (not significantly different) in natural pendular period (NPP), center-of-mass, and radius of gyration, even though they differ dis- tinctly in mass, length, moment-of-inertia, and other limb proportions. The conservation of limb NPP, despite pronounced dissimilarity in other limb characteristics, appears to be the result of systematic differences in shape, forelimbs tending to be cylindrical and hindlimbs conical. Estimating limb NPP for other species from data in the literature on segment inertia and total limb length, we present evidence that the similarity between forelimbs and hindlimbs in NPP is generally true for mammals across a large size range. Limbs swinging with or near their natural pendular periods will maximize within-limb pendular exchange of potential and kinetic energy. As all four limbs of moderate- and large-size animals swing with the same period during walking, maximal advantage can be derived from the pendular exchange of energy only if forelimbs and hindlimbs are very similar in NPP. We hypoth- esize that an important constraint in the evolution of limb length and shape is the locomotor economy derived from forelimbs and hindlimbs of similar natural pendular period. J. Morphol. 234:183-196, 1997. r 1997 Wiley-Liss, Inc. Limbs and their movements are central elements of terrestrial locomotion in mam- mals. Aspects of limb morphology that have been studied and discussed include: scaling of limb parameters (e.g., Alexander, '77; Alex- ander et al., '79; Biewener, '83; Steudel and Beattie, '93), effect of distribution of limb mass on the cost of locomotion (artificial loads: Myers and Steudel, '85; Martin, '85; Steudel, '90a; Myers et al., '93; natural varia- tion in shape: Howell, '44; Taylor et al., '74, Hildebrand and Hurley, '85), limb and limb segment lengths as predictors of maximal running speed (Garland and Janis, '93) or locomotor efficiency (e.g., Klein et al., '87; Kram and Taylor, '90; Janis and Wilhelm, '93; Steudel and Beattie, '95), and limb iner- tia or length as determinants of stride times or lengths (Alexander and Jayes, '83; Turvey et al., '88; Witte et al., '91).

Early development of chondrocranium in the tailed frog Ascaphus truei (Amphibia: Anura): Implications for anuran palatoquadrate homologies

Abstract: Chondrocranial development in Ascaphus truei was studied by serial sectioning and graphical reconstruction. Nine stages (21-29; 9-18 mm TL) were examined. Mesodermal cells were distinguished from ectomesenchymal (neural crest derived) cells by retained yolk granules. Ectomesenchymal parts of the chondrocranium include the suprarostrals, pila preoptica, anterior trabecula, and palatoquadrate. Mesodermal parts of the chondrocranium include the orbital cartilage, posterior trabecula, parachordal, basiotic lamina, and otic capsule. Development of the palatoquadrate is as follows. The pterygoid process first connects with the trabecula far rostrally; their fusion progresses caudally. The ascending process connects with a mesodermal bar that extends from the orbital cartilage to the otic capsule, and forms the ventral border of the dorsal trigeminal outlet. This bar is the "ascending process" of Ascaphus adults; it is a neurocranial, not palatoquadrate structure. The basal process chondrifies in an ectomesenchymal strand running from the quadrate keel to the postpalatine commissure. Later, the postpalatine commissure and basal process extend anteromedially to contact the floor of the anterior cupula of the otic capsule, creating separate foramina for the palatine and hyomandibular branches of the facial nerve. Based on these data, and on comparison with other frogs and salamanders, the anuran anterior quadratocranial commissure is homologized with the pterygoid process of salamanders, the anuran basal process (= "pseudobasal" or "hyobasal" process) with the basal process of salamanders, and the anuran otic ledge with the basitrabecular process of salamanders. The extensive similarities in palatoquadrate structure and development between frogs and salamanders, and lacking in caecilians, are not phylogenetically informative. Available information on fossil outgroups suggests that some of these similarities are primitive for Lissamphibia, whereas for others the polarity is uncertain.

Adaptive differentiations of the skin of the head in a subterranean rodent, Spalax ehrenbergi.

Abstract: The skin of macroscopically distinct regions (hairy skin, vibrissal fields, buccal ridge, and rhinarium) of the head of the blind mole-rat, Spalax ehrenbergi, was studied by routine histological methods. Few guard and several soft vellus hairs are organized into tufts that grow from a group of hair follicles localized in an invaginated compound cavity. We suggest that this hair arrangement may be a burrowing adaptation to match frictional resistance. The follicles and the compound cavity possess either well developed complex striated musculature or errector pili muscles. There are no structural specializations (sweat glands, glomus bodies) to enhance thermoregulatory (heat dissipative) capacities in the hairy skin of the head. Vibrissae penetrate the epidermal surface as single hairs. They are microscopically normally developed and arranged in vibrissal fields according to a basal mammalian pattern. Most of them are, however, relatively short and inconspicuous. The mystacial vibrissal field is horizontally divided by a prominent buccal ridge which is probably involved in bulldozing. The hairs in the ridge leave the compound cavity singularly. The follicles of guard hairs and bristles are equipped with well developed pilo-Ruffini complexes indicating that the buccal ridge may serve also as a tactile organ. The glabrous skin of the rhinarium has a highly interdigitated dermal-epidermal interface. The dermal papillae possess simple lamellated and/or simple Meissner's corpuscles and few Merkel cell-axon-complexes indicating that the skin of the rhinarium may be particularly sensitive to perception of vibrations.

Embryogenesis of the mayfly Ephemera japonica McLachlan (Insecta: Ephemeroptera, Ephemeridae), with special reference to abdominal formation.

Abstract: Embryogenesis of the mayfly Ephemera japonica is described, with special reference to the abdominal morphogenesis. Cleavage is of the typical superficial type. The germ disc is formed by the cell concentration of the embryonic area broadly defined at the posterior half of the blastoderm. The embryo undergoes embryogenesis of the typical short germ type. Blastokinesis in which the extensive and deep invagination of the embryo is involved is similar to those of odonatans and plecopterans. In the longest embryo stage, the abdomen is folded and is divided into four regions (regions I-IV, from anterior to posterior). All the first to eleven segments are derived from regions I and II. Regions III and IV fuse together to form the proctodaeum. This manner of abdominal formation may be regarded as basic in pterygote insects, because a similar manner is found in another palaeopteran group, the odonatans. The caudal filament has been interpreted as the elongation of the eleventh abdominal tergum, but it is now revealed that the caudal filament originates from the posterior extremity of region IV and that its origin is away from the eleventh segment, with regions III and IV or the proctodaeum interposing between. Thus, it is concluded that the caudal filament should be correlated not to the eleventh abdominal segment but to the telson. J. Morphol. 234:97-107, 1997. © 1997 Wiley-Liss, Inc.

Morphology and development of the multiple lateral line canals on the trunk in two species of Hexagrammos (Scorpaeniformes, Hexagrammidae).

Abstract: The morphology and development of the multiple lateral line canals (canals 1-5 in dorsal to ventral sequence) on the trunk of two representative hexagrammids, Hexagrammos decagrammus and H. stelleri, were studied using histological and cleared and stained material. The morphology of the lateral line scales of which the lateral line canals are composed and the distribution of canal neuromasts within them were described quantitatively. We hypothesized that 1) one neuromast is contained in each lateral line scale and all five canals contain neuromasts, 2) all five canals develop similarly, and 3) the multiple trunk canals are an adaptation for the alteration of lateral line function. Lateral line scale morphology was found to be similar among the five canals in Hexagrammos decagrammus and H. stelleri. However, canal 3 is significantly wider than the other four canals. It is the only one of the five canals connected to the canals on the head, and more significantly, it is the only one of the five canals that contains neuromasts. The lateral line scales that comprise all five lateral line canals show the same pattern of development whether or not they contain neuromasts. The five canals develop asynchronously, and each of the canals develops either rostro-caudally or caudo-rostrally. Canal 3 is the homologue of a single trunk canal in other teleosts; canals 1, 2, 4, and 5 are apomorphic features of the two species of Hexagrammos. Canals 1, 2, 4, and 5 cannot be functional components of the lateral line system because they do not contain neuromasts and thus cannot be adaptations for the alteration of lateral line function. The occurrence of lateral line canals lacking neuromasts demands a direct assessment of neuromast distributions in the lateral line canals among fishes. Finally, our data suggest that the putative role of neuromasts in the morphogenesis of lateral line canals and the nature of neuromast-bone relationships need to be critically reevaluated. J. Morphol. 233:195-214, 1997. © 1997 Wiley-Liss, Inc.

Ontogeny and limb bone scaling in two New World Marsupials, monodelphis domestica and Didelphis virginiana.

Abstract: This study examines the growth of two species of marsupials who share common ancestry and are born at the same neonatal size of a little less than 1 g. Despite this similarity at birth, adult size of these two species differs by about 50 times, with the smaller species believed to be the more ancestral. We quantified the growth in the limb bones (humerus, femur, ulna, tibia, metacarpal, and metatarsal) beginning around 40 days of age until adult size was reached. Results indicate that the larger species grows at a higher rate of growth as well as for a longer period of time to reach its larger adult size. Despite these differences in growth, there were few differences observed in the scaling over time of length to width in the various limb bones that were measured. The two species, although different in their adult size and the patterns of growth, maintain the same length to width proportions in each limb bone. The biggest difference between species in scaling was observed in the bones of the hands and feet, which may suggest adaptation to size and/or locomotor performance as body size increases. Despite variation in size, these heterochronic patterns do not affect the shape among adults or over evolutionary time. J Morphol 231:117–130, 1997. © 1997 Wiley-Liss, Inc.

Viviparity in the halfbeak genera Dermogenys and Nomorhamphus (Teleostei: Hemiramphidae).

Abstract: Gravid ovaries were examined histologically from two species of Nomorhamphus and 21 populations of Dermogenys. In addition, changes in dry-weight throughout gestation are provided for 15 populations. The ovaries are paired organs running along the lateral body wall and are separated along most of their length. In all specimens examined, embryos are fertilized within the ovarian follicle. Viviparity in these species is divided herein into five categories designated types I-V. In types I and II the entire gestation period is intrafollicular, whereas in types III-V only the early stages of gestation are intrafollicular with the major period of development occurring in the ovarian lumen (intraluminal). Type I is characterized by the retention of a large amount of yolk throughout gestation. Superfetation is not observed. Populations of D. pusilla from Vietnam and Thailand decrease in dry-weight throughout gestation. This, coupled with the slight vascularization of the yolk sac, suggests strict lecithotrophy. Populations of D. pusilla from Singapore and Bangladesh undergo an increase in dry weight and exhibit an increased vascularization of the yolk sac, suggesting a form of unspecialized matrotrophy. Type II is characterized by a small amount of yolk, an expansion of the coelomic cavity and pericardial sac, and a simple cuboidal epithelium on the general body surfaces. Superfetation occurs with up to three broods present within a single ovary. Dermogenys pusilla from Sabah, D. orientalis and Dermogenys sp. (Sulawesi) exhibit the type II form of viviparity. Dermogenys vivipara from the eastern Philippine islands of Culion and Busuanga exhibit characteristics considered intermediate between type I and II. These results are compared with those from other viviparous species exhibiting intrafollicular gestation. In species with types III-V (intraluminal gestation), developing oocytes are restricted to a distinct ridge of ovigerous tissue extending along the entire length of the ovary. Two species, D. viviparus (Luzon, Philippines) and Dermogenys sp. (Luzon) have the type III form of viviparity. In this form, oocytes are small (0.8-1.0 mm) with little yolk reserves and embryos, covered with a simple cuboidal epithelium and possessing an expanded belly sac, are retained within the follicles until a late fin-bud stage. Type III embryos found within the ovarian lumen have a greatly expanded belly sac and remain covered by a simple cuboidal epithelium until parturition. Superfetation is present in these species with two broods observed simultaneously within a single ovary. Five species, D. megarrhamphus, D. weberi, D. viviparus (Jolo, Philippines), Nomorhamphus sp. (Sulawesi), and N. towoetii, were observed with the type IV form of viviparity. Embryos in this category are evacuated into the ovarian lumen prior to a fin-bud stage and retain a large yolk mass throughout development. Superfetation is absent in these species. A differentform of viviparity (type V) is present in D. ebrardtii in which embryos appear to obtain nutrients through a form of oophagy and aldelphophagy (feeding on developing oocytes or less-developed siblings). In all specimens with intraluminal development, atretic oocytes within the ovigerous ridge are abundant. These findings support the hypothesis that current species and generic limits may be artificial and underscores the potential of histological evidence for phylogenetic analysis of this group. J. Morphol. 234:295-317, 1997. © 1997 Wiley-Liss, Inc.

Anatomy and histochemistry of spread‐wing posture in birds. 2. Gliding flight in the California Gull, Larus californicus: A paradox of fast fibers and posture

Abstract: Gliding flight is a postural activity which requires the wings to be held in a horizontal position to support the weight of the body. Postural behaviors typically utilize isometric contractions in which no change in length takes place. Due to longer actin-myosin interactions, slow contracting muscle fibers represent an economical means for this type of contraction. In specialized soaring birds, such as vultures and pelicans, a deep layer of the pectoralis muscle, composed entirely of slow fibers, is believed to perform this function. Muscles involved in gliding posture were examined in California gulls (Larus californicus) and tested for the presence of slow fibers using myosin ATPase histochemistry and antibodies. Surprisingly small numbers of slow fibers were found in the M. extensor metacarpi radialis, M. coracobrachialis cranialis, and M. coracobrachialis caudalis, which function in wrist extension, wing protraction, and body support, respectively. The low number of slow fibers in these muscles and the absence of slow fibers in muscles associated with wing extension and primary body support suggest that gulls do not require slow fibers for their postural behaviors. Gulls also lack the deep belly to the pectoralis found in other gliding birds. Since bird muscle is highly oxidative, we hypothesize that fast muscle fibers may function to maintain wing position during gliding flight in California gulls.

Sperm storage in the spermatheca of the red‐back salamander, Plethodon cinereus (Amphibia: Plethodontidae)

Abstract: In northern Indiana, the mating season of Plethodon cinereus occurs after hibernation from March until June, when oviposition begins During the mating season, a female stores sperm in its spermatheca, a compound tubular gland in the roof of the cloaca The apical cytoplasm of the spermathecal epithelium is filled with large secretory vacuoles whose product is released while sperm are stored Females induced to oviposit in June and July by injections of human chorionic gonadotropin (hCG) still retain much sperm 1 month after oviposition, but secretory vacuoles are absent in all specimens sacrificed in July and August Instead, some sperm are embedded in the spermathecal epithelium with resultant spermiophagy involving lyso- somes A female sacrificed in September 2 months after oviposition possesses scant sperm, but spermiophagy alone does not seem extensive enough to account for the decrease in sperm numbers Females sacrificed in October prior to hibernation lack sperm in their spermathecae; some secretory vacu- oles are present, but they are not as numerous or as enlarged as in specimens collected in March and May Inter- and intrafamilial differences in the cytology of sperm storage may not be phyletically informative at the family level but related to species-specific reproductive adaptations J Morphol 234:131-146, 1997 r 1997 Wiley-Liss, Inc

Anatomy and histochemistry of spread-wing posture in birds. I. Wing drying posture in the double-crested cormorant, Phalacrocorax auritus.

Abstract: Spread-wing postures of birds often have been studied with respect to the function of behavior, but ignored with regard to the mechanism by which the birds accomplish posture. The double-crested cormorant, Phalacrocorax auritus, was used as a model for this study of spread-wing posture. Those muscles capable of positioning and maintaining the wing in extension and protraction were assayed histochemically for the presence of slow (postural) muscle fibers. Within the forelimb of Phalacrocorax, Mm. coracobrachialis cranialis, pectoralis thoracicus (cranial portion), deltoideus minor, triceps scapularis, and extensor metacarpi radialis pars dorsalis and ventralis were found to contain populations of slow-twitch or slow-tonic muscle fibers. These slow fibers in the above muscles are considered to function during spread-wing posture in this species. J Morphol 233:67-76, 1997. © 1997 Wiley-Liss, Inc.