Ultrastructure of Stylodinium Iittorale (Dinophyceae) with special reference to the stalk and apical stalk complex

The ultrastructure of Stylodinium littorale Horiguchi et Chihara, a marine, sand-dwelling coccoid dinoflagel-late, was investigated with special emphasis on its stalk and the apical stalk complex. The dinoflagellate alternates between non-motile and motile cells in its life cycle. The non-motile cell possesses a long and distinct stalk. The stalk, consisting of a main cylindrical part and a holdfast, is firmly attached to a thecal plate (the apical pore plate). A part of its proximal portion is hollow and V-shaped in section. The V-shaped hollow space is underlain by a projection from the apical pore plate. An apical stalk complex is present in the motile cells and consists of a large apical pore plate and mucilaginous material. The apical pore plate is depressed into the cell, but has a narrow central tubular projection. The mucilaginous stalk-building material is stored between this plate and the outer plate membrane. The tubular projection of the apical pore plate corresponds to the apical pore of other dinoflagellates and its lumen is filled with electron-dense material. The structure of the apical stalk complex is compared with the homologous structure in Bysmatrum arenicola, the only other example of an apical stalk complex that has been investigated. A general ultrastructural survey revealed that S. littorale possesses a typical dinoflagellate cellular structure.     

The pretarsus of salticid spiders

The pretarsus of Phidippus audax (Hentz) consists of two claws flexibly articulated to a central claw lever which is flanked on either side by a curved plate of tenent setae. The claw apparatus allows for retraction of the claws by means of a dorsal cuticular cable of the pretarsal levator, while extension involves the pull of the pretarsal depressor on a ventral cable attached to the claw lever. A series of slit sensilla are strategically situated on either side of this lever. The anterior and posterior claws of the pretarsus differ in the number and spacing of their constituent teeth. The claw tufts are composed of specialized setae which account for the mechanical traction of the foot-pads. Whorled and filamentous setae of the distal tarsus are associated with the pretarsus. Comparable structures are found on other salticids.     

Fate of the anterior neural ridge and the morphogenesis of the xenopus forebrain

The fate of the anterior neural ridge was studied by following the relative movements of simultaneous spot applications of DiI and DiO from stage 15 through stage 45. These dye movements were mapped onto the neuroepithelium of the developing brain whose shape was gleaned from whole-mount in situs to neural cell adhesion molecule and dissections of the developing nervous system. The result is a model of the cell movements that drive the morphogenesis of the forebrain. The midanterior ridge moves inside and drops down along the most anterior wall of the neural tube. It then pushes forward a bit, rotates ventrally during forebrain flexing, and gives rise to the chiasmatic ridge and anterior hypothalamus. The midanterior plate drops, forming the floor of the forebrain ventricle, and, keeping its place behind the ridge, it gives rise to the posterior hypothalamus or infundibulum. The midlateral anterior ridge slides into the lateral anterior wall of the neural tube and stretches laterally into the optic stalk and retina, and then rotates into a ventral position. The lateral anterior ridge converges to the most anterior part of the dorsal midline during neural tube closure, then rotates anteriorly, and gives rise to telencephalic structures. Whole-mount bromodeoxyuridine labeling at these stages showed that cell division is widespread and relatively uniform throughout the brain during the late neurula and early tailbud stages, but that during late tailbud stages cell division becomes restricted to specific proliferative zones. We conclude that the early morphogenesis of the brain is carried out largely by choreographed cell movements and that later morphogenesis depends on spatially restricted patterns of cell division. © 1995 John Wiley & Sons, Inc.     

滇东中泥盆统的节甲鱼类化石

本文记述了节甲鱼类中称为北极鱼类的三个新属种:Exutaspis megista,Kunmingolepislucaowanensis,Yangaspis jinningensis,化石分别采自武定海口组(广义),海口和晋宁的海口组。代表我国中泥盆世该类化石鱼类的首次记述。     

Microscopic anatomy and fine structure of the skeleton-heart-kidney complex in <Emphasis Type="Italic">Saccoglossus mereschkowskii</Emphasis> (Hemichordata,Enteropneusta): 1. Stalk skeleton

This is the first paper of the series devoted to the microscopic anatomy and fine structure of the skeleton-heart-kidney complex in the acorn worm Saccoglossus mereschkowskii Wagner 1885. The skeleton of S. mereschkowskii consists of the unpaired anterior plate (lamina imparis) and two posterior horns (corni). The anterior plate bears a pair of lateral wings (alae laterales), the midventral keel (carina ventralis), the central fossa (fossa centralis) with the bordering ridge (crista circumflexa fossae centralis), two symmetrical supporting saucers (subiculi), and the conical rostrum (rostrum). The skeleton is an accretion (overgrowth) of the basal lamina between the epidermis and the endodermal epithelium of the buccal diverticulum (in the anterior part) and between the endodermal epithelia of the buccal diverticulum and the gut (in the posterior part) and consists of collagen fibers, mostly longitudinal. In all representatives of the Enteropneusta studied to date, the skeleton is a wishbone-like structure with the unpaired anterior plate and paired posterior horns, but its components widely vary in shape between species. In the family Harrimaniidae, the horns are long, and the anterior plate is rod-shaped. In the Ptychoderidae, the horns are short, and the anterior plate is rectangular. In the Spengelidae, the skeleton has an intermediate shape.     

STUDIES OF SPERMATOGENESIS IN THE HEPATICAE : II. Blepharoplast Structure in the Spermatid of Marchantia

The blepharoplast in a young, developing spermatid of Marchantia polymorpha, is a composite structure consisting of two basal bodies and a subjacent narrow band of axonemal-type tubules that we have termed the "spline." For most of its length, the spline consists of six long parallel tubules that nearly encircle the cell. The spline anterior is asymmetrically widened for about 2 µ by shorter tubules of the same kind. The lateral displacement of three long, adjacent marginal tubules by three short intervening tubules at the spline tip produces a long narrow aperture. Distally, the aperture is closed by the convergence of the displaced tubules with another trio of long tubules. Together, these form the six-membered cell-encircling portion. The expanded spline anterior has, at this stage of development, the four-layered (Vierergruppe) structure, of which the aforementioned tubules constitute the uppermost layer. The lower three strata consist of diagonal fins, elongated chambers, and fine tubules, respectively. The two flagellar bases lie close above the spline tip—one slightly anterior to the other—and diverge unequally from the spline axis. A few triplets extend proximally from the basal bodies, but do not connect with the spline. The anterior basal body is longer than the posterior one.     

The Floral Nectaries of Hibiscus rosa-sinensis: 1. Development of the Secretory Hairs

Floral nectaries of Hibiscus rosa-sinensis occur on the lowerinner side of the fused sepals and each one consists of numerous(50000–55000) secretory hairs, occupying a cylinder-likezone completely lining the inner side of the sepals. Each hairoriginates from a single protodermal mother cell and, at maturity,it is built up of a basal cell, a stalk, 35–40 intermediatecells and a tip secretory cell. Development of protodermal cellsinto secretory hairs is asynchronous, the first cells to initiatedevelopment being those situated in the lowermost part of thecylindrical zone, and development progressing upwards. Volume increase of protodermal mother cells initiating developmentis accompanied by cell polarization manifested by organelledisplacement towards the apical region. Secretory hairs areformed through a sequence of transverse and, later on, anticlinaldivisions. Divisions of apical cells are preceded by well definedpre-prophase microtubule bands, which foreshadow the plane ofthe forthcoming division and predict with accuracy the sitesof parental walls where the new cell plate fuses at cytokinesis. Stalks consist of either one or two cells. Two-celled stalksoccur in 40 per cent of secretory hairs and derive from a transversedivision of one stalk cell; the wall formed is always depositedparallel to the proximal and distal walls, but never to thelateral ones. The significance of this mode of division is discussedin relation to the fact that lateral walls are entirely impregnatedwith a cutin-like material that blocks apoplastic movement ofsolutes. Hibiscus rosa-sinensis, nectaries, development, preprophase microtuble bands, stalk cells     

Morphogenesis and histology of large scales of batoids (Elasmobranchii)

Large scales occur only in three families of batoids. Though they have a wide spectrum of different shapes they all serve protective functions in bottom-dwelling species. The crown consists of enameloid, orthodentine and osteodentine. Three different types of basal plates occur: (a) thin basal plate consisting of acellular bone; (b) basal plate which is secondarily thickened; it consists of massive acellular bone and thin denteons which surround the vascular canals; (c) basal plate which is secondarily thickened, consisting of a peculiar type of microspongy bone which has never been found in other elasmobranchs. The scales have either one or several crown elements. None of the scales, however, belongs to a growing type. All large scales were probably replaced regularly. It is the first time that dentine was found within the basal plate of an elasmobranch scale.     

Variability of the nectaries of the genusTurritis

Summary The monotype genusTurritis L. has lateral and median nectaries. The Iateral ones forming either a continuous ring or have the form of a horseshoe-shaped ridge open at the back. The median nectaries form a continuous ridge, sometimes enlarged in the median, sometimes being two-lobed.     

Comparative ultrastructure of the epidermal ciliary rootlets and associated structures in species of the Nemertodermatida and Acoela (Plathelminthes)

 The fine morphology of epidermal ciliary structures in four species of the Nemertodermatida and four species of the Acoela was studied, with emphasis on Meara stichopi (Nemertodermatida). The cilium of M. stichopi has a distal shelf and is proximally separated from the basal body by a cup-shaped structure. The bottom of the cup consists of a bilayered dense plate, or basal plate. The basal body consists of peripheral microtubule doublets continuous with those of the cilium. In the upper part of the basal body, the doublets are set at an angle and are anchored to the enclosing cell membrane by Y-shaped structures. The lower part of the basal body tapers eventually. The striated main rootlet arises on the anterior face of the basal body, initially like a flattened strap, and continues along the basal body shaped as a tube which further down becomes solid. The hour-glass-shaped posterior rootlet arises on the posterior face of the basal body. Contrary to the main rootlet, the striations in the proximal part of the posterior rootlet run parallel to the microtubule doublets of the basal body. A pair of microtubule bundles lead from the posterior rootlet to the two main rootlets in the hind ciliary row, and follow these to their lower tip. In the other species of the Nemertodermatida studied, the structure of the ciliary basal body and the ciliary rootlets is similar to that of M. stichopi. Structural differences in the species of the Acoela are that the lowermost end of the basal body is narrow and bent forwards, the proximal part of the main rootlet is trough-shaped, the main rootlet is accompanied by a pair of lateral rootlets and the posterior rootlet with associated microtubule bundles is thin. The epidermal ciliary structures in species of the Nemertodermatida and Acoela have a number of shared characters which are unique within the Plathelminthes. However, almost all of these characters are found in Xenoturbella bocki (Xenoturbellida), and some even in species of other ”phyla” of the ”lower” Metazoa. Hence, these characters cannot be considered apomorphic for the Acoelomorpha. A character seemingly present only in species of the Nemertodermatida and Acoela is the bilayered dense plate. This feature might represent an autapomorphic character state for the Acoelomorpha. Accepted: 7 March 1997     

Host location and oviposition in a basal group of parasitic wasps: the subgenual organ, ovipositor apparatus and associated structures in the Orussidae (Hymenoptera, Insecta)

Anatomical studies and behavioural observations indicate that representatives of the Orussidae use vibrational sounding to detect suitable oviposition sites. During host location, vibrations generated by tapping the tips of the antennae against the wood are picked up by the fore legs through the basitarsal spurs, transmitted along the basitarsi to thin-walled areas on the tibiae and through haemolymph to the subgenual organs, where they are transduced into nerve impulses. The apical antennomeres are distinctly shaped and have the cuticle thickened distally. The fore basitarsi have weakly sclerotised basitarsal lines proximally and membranous basitarsal spurs distally. The external wall of the fore tibiae have thin-walled areas distally on their posterior parts. Internally, large subgenual organs are situated opposite the thin-walled areas and each organ consists of 300–400 scolopidial units suspended between a lateral cuticular spine, a ventral sheet and a median ridge. The ovipositor is several times the length of the body of the wasp. When at rest, it extends all the way into the prothorax, where it is coiled before extending posteriorly to lie between the third valvulae distally. The ovipositor lies in a membranous ovipositor sac attached posteriorly to the proximal parts of the ovipositor apparatus and the posterior margin of sternum 7. In the ovipositor apparatus, the anterior parts of the second valvifers are displaced and expanded anterodorsally, inverting the first valvifers and the base of the ovipositor. When in use, the ovipositor is extended and retracted by median apodemes situated on the anterior margins of abdominal sterna 3–7. Longitudinal muscles between the apodemes allow the latter to grip the ovipositor in troughs between them. The ovipositor extends from the abdomen at the tip of sternum 7, and an internal trough on sternum 7 serves to guide the ovipositor into the wood. Despite the alterations observed in the ovipositor apparatus in the Orussidae, the musculature is almost complete and the mode of operation presumably not much different from that of other representatives of the Hymenoptera. The different ways parasitic wasps with very long ovipositors handle and accommodate these and the implications for the evolutionary history of Hymenoptera are discussed. Accepted: 14 March 2001     

PORGUENIA PERUVIANA GEN. ET SP. NOV., A MARINE CENTRIC DIATOM WITH AN UNUSUAL OCELLUS1

A new diatom genus and species, Porguenia peruviana Sullivan, is described from an Eocene marine deposit from the Paracas Peninsula, Peru. The value outline is circular and the areolation is best described as pseudoloculate; spines of any type are lacking. A ring of elongated, densely packed rimoportulae is situated on the secondary marginal ridge. Externally, each rimoportula consists of a long, flattened, fluted upper portion supported by a shorter cylindrical stalk. The processes are winged and exhibit various degrees of curvature of the major axis. Typically, six reniform ocelli of unusual structure are situated centrifugally to the ring of rimoportulae and interrupt the true marginal ridge. Because the perforation plate differs from that of all other ocellus-bearing diatoms, a new term has been introduced for this structure, the diaphoron. The placement and structure of this newly discovered “perforation plate” do not allow Porguenia to be placed in any circumscribed family, although the Triceratiaceae would appear at present to be the most closely related family.     

PORGUENIA PERUVIANA GEN. ET SP. NOV., A MARINE CENTRIC DIATOM WITH AN UNUSUAL OCELLUS1

A new diatom genus and species, Porguenia peruviana Sullivan, is described from an Eocene marine deposit from the Paracas Peninsula, Peru. The valve outline is circular and the areolation is best described as pseudoloculate; spines of any type are lacking. A ring of elongated, densely packed rimoportulae is situated on the secondary marginal ridge. Externally, each rimoportula consists of a long, flattened, fluted upper portion supported by a shorter cylindrical stalk. The processes are winged and exhibit various degrees of curvature of the major axis. Typically, six reniform ocelli of unusual structure are situated centrifugally to the ring of rimoportulae and interrupt the true marginal ridge. Because the perforation plate differs from that of all other ocellus-bearing diatoms, a new term has been introduced for this structure, the diaphoron. The placement and structure of this newly discovered “perforation plate” do not allow Porguenia to be placed in any circumscribed family, although the Triceratiaceae would appear at present to be the most closely related family.     

Cytoarchitectonic subdivisions in the subtectal midbrain of the lizard Gallotia galloti

Contemporary study of molecular patterning in the vertebrate midbrain is handicapped by the lack of a complete topological map of the diverse neuronal complexes differentiated in this domain. The relatively less deformed reptilian midbrain was chosen for resolving this fundamental issue in a way that can be extrapolated to other tetrapods. The organization of midbrain centers was mapped topologically in terms of longitudinal columns and cellular strata on transverse, Nissl-stained sections in the lizard Gallotia galloti. Four columns extend along the whole length of the midbrain. In dorsoventral order: 1) the dorsal band contains the optic tectum, surrounded by three ventricularly prominent subdivisions, named griseum tectale, intermediate area and torus semicircularis, in rostrocaudal order; 2) a subjacent region is named here the lateral band, which forms the ventral margin of the alar plate and also shows three rostrocaudal divisions; 3) the basal band forms the basal plate or tegmentum proper; it appears subdivided into medial and lateral parts: the medial part contains the oculomotor and accessory efferent neurons and the medial basal part of the reticular formation, which includes the red nucleus rostrally; the lateral part contains the lateral basal reticular formation, and includes the substantia nigra caudally; 4) the median band contains the ventral tegmental area, representing the mesencephalic floor plate. The alar regions (dorsal and lateral) show an overall cellular stratification into periventricular, central and superficial strata, with characteristic cytoarchitecture for each part. The lateral band contains two well developed superficial nuclei, one of which is commonly misidentified as an isthmic formation. The basal longitudinal subdivisions are simpler and basically consist of periventricular and central strata.     

曲靖西冲鱼(Xichonolepis qujingensis)化石的新材料及对其某些形态特征的讨论

<正> 曲靖西冲鱼(Xichonolepis qujingensis P'an et Wang)是1978年潘江、王士涛二同志为胴甲鱼建立的一个属种。化石产在云南曲靖翠峰山徐家冲与西冲之间中泥盆统海口组的下部。建立这一属种的标本有躯甲上一件骨片的内、外印模(原作者认为系前中背片)和若干属于头甲和胸鳍甲某些散落骨片的内、外印模,材料不多,保存也不甚完好。本文系对曲靖西冲鱼形态特征的补充记述,标本是刘玉海、王俊卿和笔者等自1962年以来陆续在滇东中泥盆统采获的。最初,在武定赵家庄后山的泥灰岩层与刘氏滇鱼     

Relationship of the central ACTH-immunoreactive opiocortin system to the median eminence and the pituitary gland of the rat

Summary By immunocytochemical methods, the present study describes ACTH-immunoreactive fibers in the pituitary stalk and neural lobe. This opiocortin-hypothalamo-neural lobe projection arises in a bed nucleus of perikarya in the basal hypothalamus, follows supraoptico-hypophyseal fibers in the zona interna of the median eminence, and distributes throughout the neural lobe. No ACTH-immunoreactive fibers project to the zona externa; some are present in the subependymal layer and at the lateral margins of the median eminence. Further studies must identify the role of these fibers in posterior lobe function. It remains also to be determined whether this system terminates upon primary pituitary portal capillaries and delivers opiocortin neuropeptides to the adenohypophysis.Supported by NIH Grants HD-07962, NS-15345 and AM-22029The skillful technical assistance of Donna Wilson, Nancy Dembs and Jay Hocton is thankfully acknowledged     

Role of cell-cycle in regulating neuroepithelial cell shape during bending of the chick neural plate

Summary Neuroepithelial cells transform from spindle-shaped to wedge-shaped within the median and paired dorsolateral hinge points of the bending neural plate, but the mechanisms underlying these localized changes are unclear. This study was designed to evaluate further the hypothesis that localized wedging of neuroepithelial cells during bending involves basal cellular expansion resulting from alteration of the cell-cycle. Neurulating chick embryos were treated with tritiated thymidine, and transverse sections through the midbrain were examined autoradiographically. Parameters of the cell-cycle as well as nuclear position and size were assessed in the median hinge point, which contains predominantly wedge-shaped cells, and in adjacent lateral areas of the neural plate, which contain predominantly spindle-shaped cells. Both the DNA-synthetic phase and non-DNA synthetic portion of the cell-cycle were significantly longer in the median hinge point than in lateral neuroepithelial areas, some nuclei in both regions were located basally during these phases, and virtually all basal nuclei in the median hinge point were large. Additionally, the mitotic phase was significantly shorter in the median hinge point than in lateral areas. We present a model to explain how alteration of the cell-cycle in the median hinge point could generate wedging of cells in this region.     

Cicesetrema unami n. gen., n. sp. (Digenea: Cryptogonimidae: Cryptogoniminae) from Paralichthys californicus (Ayres, 1859) (Osteichthyes: Pleuronectiformes: Paralichthydae) in San Quintin Bay, Baja California, Mexico

Cicesetrema unami n. gen., n. sp. (Digenea: Cryptogonimidae) is described from the intestine of the California halibut, Paralichthys californicus, from San Quintin Bay, Baja California, Mexico. The new genus is distinguished from other members of the Cryptogoniminae in having vitellaria that form asymmetric bunches of follicles and extend in lateral fields from the level of the ovary posteriad beyond the testes. In addition, the species in the new genus possess a subterminal, funnel-shaped oral sucker that is prominent when protruded but usually retracted in a fold at the anterior end.     

Description of Auriculotrema lechneri n. gen., n. sp. (Digenea: Choanocotylidae), a parasite of freshwater turtles (Testudines: Pleurodira: Chelidae) from Queensland,Australia

Auriculotrema lechneri n. gen., n. sp. is described from the small intestine of Emydura krefftii and Elseya latisternum from northern Queensland, Australia. The new species strongly resembles species of Choanocotyle in body shape, ventral incision of the oral sucker, structure of the cirrus sac, and location of the genital pore. The distinctive taxonomic feature is the presence of 2 winglike projections extending beyond the lateral margins of the oral sucker, in contrast to the extremely large, expanded oral sucker diagnostic of Choanocotyle spp. Auriculotrema n. gen. is the second genus included in the formerly monotypic Choanocotylidae Jue Sue and Platt, 1998.