摘要:

AbstractThe larval ciliary bands of echinoderm bipinnaria and pluteus larvae and the hemichordate tornaria contain similar multipolar or bipolar nerve cells with unusual apical processes that run across the surface of the band between the bases of its cilia. We report on some distinctive ultrastructural features of these cells. Among these are specialized junctions that occur between the cells' apical processes and adjacent ciliary band cells near the base of each cilium. Such structures are best developed in pluteus larvae. Many nerve cells in the larval spinal cord of amphioxus also have large apical processes that cross the central lumen of the cord. We interpret our observations on these cells in terms of Garstang's hypothesis, which derives the chordate neural tube from a larval ciliary band, and suggest that multipolar cells like those in echinoderm and tornaria bands may be the antecedents of some categories of neurons in the chordate spinal cord.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01215.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractA previous light microscopic study of the retina ofTelescopus fallaxhas showed the presence of three types of photoreceptors: large single cones (type A), large double cones (type B), and small single rods (type D). The present electron microscopic study has demonstrated that the small single rod is a morphological cone characterized by possessing a slightly tapering outer segment and a very extensive zone of continuity between the discs and the plasma membrane of the outer segment.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01216.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe anatomy and embryology of the dipnoan snout and olfactory organ play a major role in the discussion about the phylogenetic position of Dipnoi and the question of ancestry of Tetrapoda. This is primarily due to the fact that an internal nostril is regarded as an important preadaptive organ of the ancestors of tetrapods. Two conflicting scenarios of phylogenetic change were proposed in favour of different hypotheses of relationship. One emphasizes the similarities between Dipnoi and Chondrichthyes concerning this complex of characters. The other supports the idea of a close relationship of Dipnoi and Tetrapoda and a common origin of a ‘choana’ from the posterior external nostril of fishes. Accordingly, there is need for a detailed embryological and anatomical study which could help to clarify homologies and the basis of character evaluation. This, in the first place, concentrates onNeoceratodus forsteri.A plate reconstruction of the larval head provides many new insights which are important for comparison with the lepidosirenid lungfishesProtopterusandLepidosirenand with other vertebrate taxa. The value of the peripheral nervous system as a topographical reference is critically reviewed. The results support the hypothesis that lungfish form a ‘primitive’ teleostomate group, closely adjoining Chondrichthyes in many characteristics of the snout formation. The relations between cranial nerves in the snout and the developing nasal sac, however, do not support the conclusion that the recent selachian condition is the exceptional ancestral character state of the lungfish snout. Dipnoi lack a ‘choana’, but nevertheless a closer relationship to tetrapods is not excluded. A vestigial and transitory naso‐buccal connection in larvae ofNeoceratodusmight indicate such common ancestry, but has a completely different functional significance among fishes. It is shared with several plagiostomes and is, therefore, probably not useful as a synapomorphy of Dipnoi

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01217.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractAdult and larval lamprey cartilage, normally unmineralized, was cultured in a medium meta‐stable for hydroxyapatite for periods of up to 12 days at 20, 30 or 37°C. Histochemical analysis revealed a temperature‐dependent increase over time in calcium phosphate incorporation into the extracellular matrix (ECM) of adult cartilage concomitant with the incorporation of calcium as detected by gravimetric and radioisotopic methods. Ultrastructural analysis revealed the presence of ECM dense bodies (40 nm average) containing crystalline material which increased in number with increased mineral incorporation but were absent from control cartilage. Additionally, electron‐dense particles (15–20 nm) found in close association with the ECM fibrils in some regions of mineralized cartilage may represent sites of amorphous calcium phosphate. Larval cartilage incorporated much less calcium, less uniformly over time than did adult cartilage. Histochemical and ultrastructural analysis revealed that calcium had accumulated in the chondrocytes instead of the ECM and this proved detrimental, leading to the death of the cells.The discovery that adult lamprey cartilage calcifiesin vitrounder appropriate conditions, suggests that petromyzonids, or their direct agnathan ancestors, may have possessed mineralized skeletons and that this ability is ‘repressed’ in extant lampreys owing primarily to the environment

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01218.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractActinopygid Cuvierian tubules are few in number. They are made of a basal trunk from which arises 2–3 branches. The trunk is smooth and hollow (proximally) or slightly swollen and solid (distally) and the branches consist of a central rachis to which attach many peripheral spherules. The fine structure of the tubules is similar in the three investigated species ofActinopygabut differs considerably from that of non‐actinopygid tubules. Basic behavioural differences occur also as actinopygid Cuvierian tubules cannot elongate nor become sticky, and are not expelled by the individuals. It is concluded that actinopygid Cuvierian tubules do not fulfil a defensive funct

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01219.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe genealogy of B‐cells in the hepatopancreas of decapod crustaceans is still a matter of intense debate. According to widely accepted two‐cell‐line concepts, B‐cells are supposed to originate either from secretory F‐cells or absorptive R‐cells. These concepts are based on the putative lack of B‐cells in the differentiation zone of the hepatopancreas tubules. In the giant tiger prawnPenaeus monodonI could clearly identify differentiating B‐cells in that zone by using an ultrastructural distinguishing mark, the apical complex, that is much more sensitive than markers used before. Tracking of this feature from mature B‐cells through the differentiation zone up to the embryonic E‐cells revealed that B‐cells directly originate from E‐cells. The recognition of B‐cells as a separate cell line calls for a new functional interpretation. Ultrastructural and histochemical data suggest a degrading function. B‐cells may clear the hepatopancreas tubules from remnants of digestion in the time span between nutrient absorption and secreti

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01220.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

AbstractThe blood cells of a solitary ascidian,Halocynthia roretzi, were examined by electron microscopy (EM) with reference to their appearance by light microscopy (LM). In addition, their movement and stainability by vital dyes was observed by phase‐contrast microscopy, and their stainability by Giemsa was also examined. Nine cell types were recognized: vacuolated cells, hyaline amoebocytes, small amoebocytes, granular amoebocytes, macrogranular cells, globular cells, lymphocyte‐like cells, large basophilic cells and large granular cells. Vacuolated cells were found to possess various numbers of vacuoles containing strongly electron‐dense materials and could be divided into at least three subgroups. Granular amoebocytes contained microfilaments and many granules of uniform size. Hyaline amoebocytes and small amoebocytes seemed to be specialized as phagocytes. Macrogranular cells and globular cells were not well characterized. In the blood of adult individuals, hemoblasts were rarely found, although lymphocyte‐like cells were present. Each of two large cells, large basophilic cells and large granular cells, possessed novel granules or vacuoles, whose functions remain to be elucidated. The possible functions and relationships of these cells among various ascidian species are di

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01221.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Book reviewed in this article:Verhandlungen der Deutschen zoologischen Gesellschaft 83. Jahresversammlung 1990 in Frankfurt am Main.Gustav FischerVerhandlungen der Deutschen zoologsichen Gesellschaft 84. Jahresversammlung 1991 in Tübingen.Gustav Fische

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01222.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1993.tb01223.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY