The ontogenic development of the vertebrae in some gekkonoid lizards

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

Maturing of fibrils and intraosseous osteogenesis as a basis for the development of lamellae and the osteon structure]

We investigated in continuation of lightmicroscopical (phasecontrast, polarized light) and statistical studies concerning the formation of lamellae and osteons electromicroscopical the nature of fibrils in different areas of the cross section of the metacarpus from a cattle fetus of 520 mm SSL. During the maturation of fibrils in a subperiostal trabecal the diameter of fibrils increased (465 to 470 A). The period (316 or 536 A) contains primarily only a broad band and a small interband. Subsequently the interband increased (221 or 215 A), but the band decreased (324 or 271 A). In the centre of trabeculae the fibrils formate microlamellae. The fibrils split later on in the medial part of the cross section in microfibrils with irregular oreintation and appear lightmicroscopical as intermediate tissue (blasse Mittellinie). At the same time new fibrils are synthesized around the osteocytes and their canaliculi. As the result of a kind of remodeling the fibrils arrange in a parallel order forming packages which appear lightmicroscopical as fibrous felts. These fibrous felts exhibits partly an periodical arrangement with a small band (164 A) and a wide interband (287 A). In a following stage in the fibrous felts lamellae are developed, the length of which increased around the medullary cavity. Firstly after the development of lamellae the definite bone fibrils are reconstituted (diameter: 530 A; band: 348 A; interband: 212 A). Apparently the osteocytes are responsible for these procedures in a stage specific synthetic and lytic activity. The modification of the nature of fibrils results probably after the dissolving of the structural glycoproteins, which stabilize the tropocollagen molecules. A reconstitution of the structural glycoproteins after formation of the lamellae induce the reconstitution of bone specific collagenfibrils. The regulating mechanism for the codification of these structural development are unknown.     

Fine structure of the respiratory lamellae of teleostean gills

Summary The blood-water pathway in respiratory lamellae of teleostean gills consists of an epithelial layer one or two cells thick, a basal lamina and a thin layer of cytoplasm which lines the blood lacunae. This layer of cytoplasm is formed by flange-like extensions of the pillar cells. The resulting location of the pillar cell perikarya between the surfaces of the blood lacunae is probably of paramount importance for maintenance of the flattened form of the lamellae.Collagenous bundles traverse the pillar cells within tubes formed by infolding of the cellular surface. These bundles, which are oriented normal to the flattened aspect of the lamellae, no doubt provide further protection against distension or collapse of the blood spaces. A compartment filled with collagenous tissue is interposed between the basal lamina and the lining layer of the lacunae in some of the species studied.Regulation of blood flow to the respiratory surfaces is thought to result in part from contraction of the pillar cells. This contractility presumably resides in tracts of filaments which course through the cytoplasm of the pillar cells parallel to the collagenous bundles. Since nervous tissue has not been demonstrated within the gill lamellae it is possible that contraction of the pillar cells is under some form of hormonal control, although existence of local control mechanisms (e.g. self-stimulation of the cells as a result of anoxia) is not excluded.Within the limited number of species studied, the structure of the blood-water pathway does not appear to be correlated with the characteristics of the normal habitat of a particular species.This work was performed during the tenure of a post doctoral traineeship under USPHS Grant 5 T 1 GM-136 to the Department of Biological Structure, University of Washington.Particular thanks are due Dr. John H. Luft of the University of Washington for his advice and criticism while this work was in progress and to Drs. Douglas Kelly, James Koehler and Daniel Szollosi for critical assistance with the manuscipt.     

Morphogenesis of the digital pad lamellae in the embryo of the lizard Anolis lineatopus

The present study in the embryo of the lizard Anolis lineatopus describes the modality of cell proliferation responsible for the morphogenesis of the digital pad lamellae and of the epidermal stratification. After tritiated thymidine and 5-bromodeoxy-uridine administration, autoradiographic and immunocytochemical methods have been used. The lamellae originate as long, slightly slanted, undulations of the epidermis of fingers and toes. At an early stage, the epidermis consists of an outer periderm and a basal layer. Cell hypertrophy, and the prevalent cell proliferation in the longer side of the undulation with respect to the shorter side, generate the surface of the outer lamella. Under the peridermis, a shedding complex, composed by clear and oberhautchen layers, is formed and later determines the first intraepidermal shed. The first subperidermal layer derived from the basal layer is a clear layer and the first shed epidermis in the embryo is represented by periderm and clear layer. The heavily granulated clear layer in Anolis lineatopus represents the first epidermal layer produced in the embryonic epidermis, and is connected with the process of shedding. The spinulae of the underlying oberhautchen in the outer scale surface become long setae which grow toward the upper clear layer. Under the shedding complex a β-layer is produced. Autoradiographical study shows that the radioactivity stays in the basal layer for about 4 days before cells move to upper layers. At 6–8 days post-injection labelled cells are visible in the differentiated clear, oberhautchen and β-layers. Under the β-layer differentiating mesos cells are visible before the embryo hatches.     

The structure of the carotid bifurcation in the lizards Tiliqua occipitalis and Trachysaurus rugosus

The origin of the internal carotid artery in the lizards Tiliqua occipitalis and Trachysaurus rugosus has been shown to be both extremely variable and complex. In the dense connective tissue investing the junction of the internal carotid artery and the summit of the carotid arch are groups of cells associated with sinusoids derved from arterioles arising from the neighboring great vessels. The conspicuous epithelioid cells in these groups resemble the mammalian carotid body glomus and amphibian α cells. Nerve fibers showing no obvious synaptic specializations pass to and over these cell groups. It is suggested that these cell groups and sinusoids are comparable to mammalian carotid body glomeruli. A similar group of cells has been described in the concavity of the summit of the fourth aortic arch. This cell group, however, gives a distinct chromaffin reaction.     

The ultrastructure of the chloroplast lamellae

Summary The present study has shown that the thylakoid membrane consists of a central layer, probably lipid, covered on both sides with protein particles. The thickness of the middle layer reaches 40 Å, and the diameter of the attached globules 60 Å. The particles are partially embedded to a depth of about 20 Å in the central layer. If these globules are removed, the lipid layer appears perforated, indicating that the protein molecules are in direct contact through the lipid layer. On the outer side of the thylakoid membrane the particles are grouped in fours, forming a multienzyme complex of 120 Å diameter and 60 Å thickness. No such aggregates have been observed on the inner side.In frozen plastids a tripartite membrane at the periphery of a granum has a thickness of 120 Å, whereas the two membranes of adjacent thylakoids are together only 200 Å thick. This indicates that the particles attached to the two neighbouring membranes are interlocked and form a rigid layer.In comparison with the freeze-etched preparations the chemically fixed plastids show considerably thinner lamellae. They appear as unit membranes, consisting of a central layer 35 Å thick and two dense strata, each of 20 Å. This discrepancy cannot be explained simply by shrinkage in fixation and dehydration. It is proposed that fixation causes uncoiling of the protein molecules. In consequence, thin protein films are formed on each side of the lipid layer, and each appears as a dark band after osmium- or permanganate fixation. This new model of the thylakoid membrane is compared with other recent schemes.

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Zusammenfassung In der vorliegenden Untersuchung wird gezeigt, daß die Thylakoidmembran aus einer zentralen, wahrscheinlich lipidhaltigen Schicht besteht, die beidseitig mit Proteinpartikeln bedeckt ist. Die Dicke dieser Mittelschicht beträgt 40 Å und der Durchmesser der darauf liegenden Kügelchen 60 Å. Sowohl die innern wie die äußern Partikel sind ungefähr 20 Å tief in der zentralen Schicht eingebettet. Werden sie beim Herstellen des Gefrierabdruckes herausgerissen, so erscheint die Lipoidlamelle perforiert. Das zeigt, daß die Enzyme durch diese Schicht hindurch in direktem Kontakt stehen. Auf der Außenseite der Thylakoidmembran sind vier Partikel zu einem Multi-Enzym-Komplex von 120 Å Durchmesser und 60 Å Dicke vereinigt. Auf der Innenseite konnten solche Zusammenlagerungen nicht beobachtet werden. Die Dicke einer dreischichtigen Membran, wie sie z. B. an der Außenseite eines Granumstapels zu beobachten ist, beträgt 120 Å. Die Doppelmembranen benachbarter Thylakoide (200 Å dick) sind durch die auf der Oberfläche vorhandenen Partikel eng verzahnt.Ein Vergleich der Bilder von Plastiden nach der Gefrierätzung und nach einer gewöhnlichen Fixierung ergibt, daß die Lamellen durch die Fixierung und Entwässerung dünner werden. Sie zeigen die Struktur einer Einheitsmembran bestehend aus einer 35 Å dicken Zentralschicht und den beiden anliegenden 20 Å dicken osmiophilen Lamellen. Die unterschiedliche Lamellendicke (Gefriergetrocknet: 120 Å, fixiert: 75 Å) kann nicht nur auf die bei der Fixierung und Entwässerung eintretende Schrumpfung zurückgeführt werden. Es ist wahrscheinlich, daß die Fixierung eine Entknäuelung der Proteinmoleküle bewirkt. Der dadurch auf beiden Seiten der Lipidschicht gebildete, dünne Protein-film erscheint nach der Osmium-oder Permanganatfixierung als kontrastreiche 20 Å dicke Schicht. Dieses neue Modell der Thylakoidmembran wurde mit einigen neuen Strukturschemata verglichen.

     

Aspects of vertebral development in lizards and snakes

The embryonic and postnatal development of vertebrae of the mid-trunk and mid-tail in Lacerta vivipara, Anguis fragilis and Natrix natrix have been studied. Centra and neural arches develop independently after the perichordal tube has been formed, the neurocentral suture representing a consistent boundary between them. The condyle and cup of each centrum are formed by differential growth of cartilage; in Anguis and Natrix the joints between centra are synovial. The zygosphenial joints of Lacerta are continuous with the zygapophysial joints and not separate from them as in snakes. The autotomy splits in the tail vertebrae of Lacerta are derived from four distinct components which become continuous in postnatal life. The chordal cartilage is not involved in the split formation.     

Evolution of structure and function of the hearing organ of lizards

Following their origin during the early Cretaceous, the lizards radiated early into a number of families. This radiation was accompanied by a diversification in the structure of the inner ear. The morphology of the auditory basilar papilla is family-specific, with large variations in a number of parameters. At the physiologic level, this wide variation does not result in an equivalent range of physiologic parameters. This review considers the possible influence of various morphologic features on function, and correlates these features with physiologic response parameters. Anatomical variety that does not result in significant changes in the inputs to the brain is "neutral" with regard to selection pressures. This independence apparently removed evolutionary constraints and led to some of the great variety of auditory papillae seen. Other anatomical features are more important and do produce significant effects at the level of the auditory nerve.     

Parathyroid gland structure of some tropical lizards

The number, location, size, shape and microstructure of the parathyroid glands of Agama agama agama, Hemidactylus brooki angulatus and Pytodactylus hasselquisti hasselquisti was investigated using approximately 250 specimens of each species from the Zaria area of Nigeria. Only parathyroid III was found. Additional patches of tissue in Hemidactylus, though possibly parathyroid IV, are considered to be derived from parathyroid III. It was found that the amount of parathyroid tissue per gram of body weight was similar in the three species used, and that females had more parathyroid tissue than males. The same situation seems possible in other species. The structure of the parathyroid glands could not be related to taxonomic grouping within the Sauria, but the general picture was found to be more similar to that of birds and mammals than to that of amphibians.     

The post-natal development of holocrine epidermal specializations in gekkonid lizards.

The abdominal escutcheon, and certain aspects of pre-anal organ morphology, have been studied in Sphaerodactylus spp. and Gekko vittatus respectively. These epidermal modifications are male characteristics. The sphaerodactyline escutcheon becomes larger by the peripheral addition of specialized scales with increasing size of the individuals: this relationship is much more clearcut in S. cinereus than in the notatus species group (sensu Shreves, '68), and the possible reasons for this are discussed. The number of pre-anal organs varies between populations of G. vittatus, but within populations remains constant throughout life. Individual organs increase steadily in size throughout life. These data are discussed with reference to current interpretations of gekkonid gland evolution, and of factors controlling epidermal cell proliferation and differentiation.     

An analysis of the structure of the bilaminar lamellae of the hamster egg

The unfertilized hamster egg contains a ubiquitous distribution of lamellate structures. Normally the lamellae are bilaminar, although occasionally both single sheets and multiple sheets are seen. Detailed analysis of the structure of a single bilaminar lamella shows that each sheet of the two-sheet structure is identical and made up of repeating rhombohedral units whose principal axes are in the ratio of 2:1. Each sheet lies at 90 degrees to the other. Using this information, a single bilaminar lamella has been reconstructed. This reconstruction accounts for its major ultrastructural features.     

Investigations into the structure and fixation properties of cytoplasmic lamellae in the hamster oocyte

Summary Lamellar structures have been revealed in the cytoplasm of rapidly growing hamster oocytes by glutaraldehyde fixation and by fixation in 30% ethanol followed by osmication. The structures are not preserved after osmium tetroxide either used alone or followed by glutaraldehyde; nor are they preserved by absolute ethanol, formaldehyde, glyceraldehyde, glyoxal, 2-hydroxy-adipaldehyde or potassium permanganate. Immersion in 30% ethanol followed by extraction in distilled water and fixation in glutaraldehyde and osmium tetroxide exposes the lattice-like skeletal structure of the lamellae. The lamellae are present but slightly altered after short digestion in pepsin. Longer digestion results in complete dissolution of the structures.Supported by U.S.P.H.S. Post-doctoral Fellowship 5 F2 HD-25, 190–02.I wish to thank Prof. R. E. Coupland for his continued interest in this work and for his helpful criticisms.     

Differentiation of chloroplast lamellae: Light harvesting efficiency and grana development

Incomplete development of chloroplast lamellae occurred when etiolated pea plants were greened under cycles of 2 min light, 118 min dark. Although the plastids had full photochemical activities, they were nearly agranal. They were also characterized by a high quantum requirement for whole chain electron transport in low light; this is thought to be the result of unequal light absorption by incompletely developed light-harvesting assemblies of photosystem I and II and a lack of regulation of excitation energy distribution between the two photosystems. Continuous illumination induced the final stages of membrane differentiation. These stages were primarily characterized by the appearance of grana stacking and an increase in photosynthetic unit size. A biphasic decrease in quantum requirement for whole chain electron transport correlated directly with the appearance of grana during the final steps of membrane assembly. Structural organization of the membrane may be related to the light-harvesting efficiency of the membrane.     

Embryonic development of the fossorial gymnophthalmid lizards Nothobachia ablephara and Calyptommatus sinebrachiatus

The evolutionary history of the lizard family Gymnophthalmidae is characterized by several independent events of morphological modifications to a snake-like body plan, such as limb reduction, body elongation, loss of external ear openings, and modifications in skull bones, as adaptive responses to a burrowing and fossorial lifestyle. The origins of such morphological modifications from an ancestral lizard-like condition can be traced back to evolutionary changes in the developmental processes that coordinate the building of the organism. Thus, the characterization of the embryonic development of gymnophthalmid lizards is an essential step because it lays the foundation for future studies aiming to understand the exact nature of these changes and the developmental mechanisms that could have been responsible for the evolution of a serpentiform (snake-like) from a lacertiform (lizard-like) body form. Here we describe the post-ovipositional embryonic development of the fossorial species Nothobachia ablephara and Calyptommatus sinebrachiatus, presenting a detailed staging system for each one, with special focus on the development of the reduced limbs, and comparing their development to that of other lizard species. The data provided by the staging series are essential for future experimental studies addressing the genetic basis of the evolutionary and developmental variation of the Gymnophthalmidae.     

Fine structure of the pore-annulus complex in the nuclear envelope and annulate lamellae of germ cells

Summary Octagonal symmetry in the pore margin has been demonstratedin situ in annulate lamellae and the nuclear envelope of germ cells. The annular material is located to variable extent within the pore and also extends beyond the pore margin; in the latter case it may be continuous with extra-pore annular material of some adjacent pores. In thin sections of fixed material, the annular material of both the nuclear envelope and annulate lamellae appears to be composed of a matrix within which are embedded thin filaments and small granules, the disposition and interrelationship of which are described and discussed. The so-called intra-annular granule is described as consisting of a number of smaller units (similar to the granular component of the annular material) which become aggregated in the center of some pores in both the nuclear envelope and annulate lamellae. The possible significance of intra-annular granules is discussed in terms of binding and movement of macromolecules.This investigation was supported by research grants (HD-00699, GM-09229) and a Career Development Award from the National Institutes of Health, U. S. Public Health Service. The author acknowledges the skillful technical assistance of Mrs.Robert Decker.     

Sexual selection predicts brain structure in dragon lizards

Phenotypic traits such as ornaments and armaments are generally shaped by sexual selection, which often favours larger and more elaborate males compared to females. But can sexual selection also influence the brain? Previous studies in vertebrates report contradictory results with no consistent pattern between variation in brain structure and the strength of sexual selection. We hypothesize that sexual selection will act in a consistent way on two vertebrate brain regions that directly regulate sexual behaviour: the medial preoptic nucleus (MPON) and the ventromedial hypothalamic nucleus (VMN). The MPON regulates male reproductive behaviour whereas the VMN regulates female reproductive behaviour and is also involved in male aggression. To test our hypothesis, we used high‐resolution magnetic resonance imaging combined with traditional histology of brains in 14 dragon lizard species of the genus Ctenophorus that vary in the strength of precopulatory sexual selection. Males belonging to species that experience greater sexual selection had a larger MPON and a smaller VMN. Conversely, females did not show any patterns of variation in these brain regions. As the volumes of both these regions also correlated with brain volume (BV) in our models, we tested whether they show the same pattern of evolution in response to changes in BV and found that the do. Therefore, we show that the primary brain nuclei underlying reproductive behaviour in vertebrates can evolve in a mosaic fashion, differently between males and females, likely in response to sexual selection, and that these same regions are simultaneously evolving in concert in relation to overall brain size.