摘要:

AbstractInMolgula pacificasmall previtellogenic oocytes are found between cells of the ovarian epithelium. Each oocyte subsequently grows within a compartment of the epithelium known as a primary follicle. The wall of the primary follicle is composed of outer follicular epithelial cells. While growing from about 15–70 μm in diameter, each oocyte gradually recruits a set of about 950 non‐epithelial inner follicular cells. These cells co‐differentiate in sets with each oocyte, but test cells never appear. The first filamentous components of the vitelline coat appear on the surface of an oocyte in places where it is in contact with undifferentiated (stage 2) inner follicular cells. Each fully differentiated inner follicular cell stores adhesive precursors in a large compartment of the endoplasmic reticulum and probably secretes components of the vitelline coat. There is no evidence that the outer follicular epithelial cells transform into inner follicular cells by dedifferentiation as has often been assumed. Inner follicular cells, in stage 1, are nearly identical to hemoblasts. Hemoblasts may form the inner follicular cells, but to do this they would have to cross the outer follicular epithelium and this phenomenon has not yet bee

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1995.tb00985.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFlorida lancelets were raised in laboratory cultures from the egg to the juvenile stage. At frequent intervals during development, elongation of the embryonic and larval body was measured at room temperature (22.5°C) and at the approximate temperature of the natural environment (30°C). Development was slower at the lower temperature, with metamorphosis commencing during the fifth week as compared to the third week at the higher temperature. Scanning electron microscopy (SEM) was used to describe a frequently sampled series of hatched embryos, pre‐metamorphic larvae, metamorphic larvae, and juveniles. The advent (and sometimes subsequent disappearance) of the following structures was determined from the SEM data: general epidermal ciliation, peroral pit, mouth, primary gill slits, ciliary tuft, external opening of the club‐shaped gland, sense cells, anus, metapleural folds, and preoral cirri. Our SEM did not substantiate the claims of van Wijhe for a transitory larval mouth near the anteriovental end of the larvae. The general epidermal cilation, which is uniformly distributed in the embryos, becomes somewhat reduced in the pre‐metamorphic larvae and then disappears almost entirely during metamorphosis. The epidermis includes two distinct sense cell types (I and II) and possibly a third type (the ventral pit cells, to which an adhesive role has alternatively been attributed). The anus first opens on the right‐hand side and only later migrates across the mid‐ventral line to assume a position on the left‐hand side of the larva; this is contrary to the established view that the anus of the larval lancelets opens on the left‐hand side an

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1995.tb00986.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe nervous system of the planktotrophic trochophore larva ofPolygordius lacteushas been investigated using antibodies to serotonin (5‐HT) and the neuropeptide FMRFamide. The apical ganglion contains three 5‐HT‐ir neurons, many FMRFamide‐ir neurons and a tripartate 5‐HT‐ir and FMRFamide‐ir neuropil. A lateral nerve extends from each side of the apical ganglion across the episphere and the ventral hyposphere, where the two nerves combine to form the paired ventral nerve cord. These nerves have both 5‐HT‐ir and FMRFamide‐ir processes. Three circumferential nerves are associated with the ciliary bands: two prototroch and one metatroch nerve. All contain 5‐HT‐ir and FMRFamide‐ir processes. An oral nerve plexus also contain both 5‐HT‐ir and FMRFamide‐ir processes develops from the metatroch nerve, and an esophageal ring of FMRFamide‐ir processes develops in later larval stages. In young stages the ventral ganglion contains two 5‐HT‐ir and two FMRFamide‐ir perikarya; during development the ventral ganglion grows caudally and adds additional 5‐HR‐ir and FMRFamide‐ir perikarya. These are the only perikarya that could be found along the lateral nerve and ventral nerve cord. The telotroch nerve develops from the ventral nerve cord. The 5‐HT‐ir and FMRFamide‐ir part of the nervous system is strictly bilateral symmetric. and much of the system (i.e. apical ganglion, lateral nerves ventral nerve cord, dor

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1995.tb00987.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe concept of Gösta Jägersten of a primary biphasic metazoan life‐cycle, consisting of a planktotrophic larva and a benthic adult, forms the basis for several theories on metazoan phylogeny. In this paper the assumed planktotrophic life‐style of the larva is critically analyzed and reconsidered. It is shown, in particular for the Mollusca, that a biphasic life‐cycle with a lecithotrophic larva is probably the plesiomorphic condition. Character distribution and structural data suggest a parallel evolution of the downstream collecting system used in planktotrophic larvae or filter‐feeding adults of gastropods, bivalves and other spiralian or aschelminth taxa. In the basic metazoans (Parazoa, Placozoa, coelenterates) direct or lecithotrophic development dominates by far. For the acoelomate (Platyhelminthes, Gnathostomulida) and pseudocoelomate taxa direct development is probably the plesiomorphic condition. The structural similarities of the upstream collecting system in tentaculate and deuterostome phyla may also be explained by parallel events of heterochrony out of an ancestor with adult filter‐feeding. The main conclusion of this survey is that larval planktotrophy is likely to be secondary and not a plesiomorphic condition among the Bilateria. Accordingly, theories which are based on the assumed plesiomorphy of larval planktotrophy of the Bilateria, need careful r

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1995.tb00988.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractLike many echinoderms, the seastar,Patiriella exiguahas a wrinkled blastula rather than the smooth‐walled blastula typical of most phyla. The cellular events of wrinkled blastula formation inP. exiguawere documented using light, confocal and electron microscopy. Wrinkled blastulae have a highly infolded epithelium. Prior to wrinkling, the blastomeres are cuboidal with lipid droplets and yolk granules distributed throughout their cytoplasm. During wrinkling, the cells become columnar and the lipid and yolk reserves become redistributed to the basal and apical ends of the cells, respectively. Gastrulae have a tall columnar epithelium, with a basal accumulation of lipid. Interdigitation of numerous cell projections, including short lateral processes, basal lamellipodia and apical filopodia, assists in maintaining epithelial integrity during wrinkling. Apical filopodia have not been observed in other echinoderm embryos. Although 1 M urea caused elevation of the fertilization envelope, the embryos did not expand into the newly‐created space. This is suggested to be due to the adhesive properties of the hyaline layer. Embryos removed from their envelope were enlarged with shallower and fewer wrinkles compared with controls. It appears that the integrity of the hyaline layer and fertilization envelope both influence the compact wrinkled profile ofP. exiguablastu

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1995.tb00989.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractMorphometric investigations of the gill apparatus in the pelagic Baikal sculpins (Cottocomephorinae) reveal a relatively large gill respiratory area (GRSA). Allometric relationship between GRSA and body weight is expressed by the equation: Y = 746.61W0.918forC. inermisand that Y = 655.68W0.913forC. grewingki. In calculations per body weight unit the GRSA valuesC. inermisare a little higher than those inC. grewingki. Obtained numerical data seem to be in accordance with difference in biological activity of species examined. Their GRSA is several times larger than that in previously examined the bathypelagicComephorus dybowskiiand deep bottom dwellerCottinella boulengeri.

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1995.tb00990.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractWe examined the ultrastructure of the spermatozoa from two species of eutardigrades, gonochoristicAmphibolus volubilisand hermaphroditicA. weglarskae, by scanning and transmission electron microscopy. The gametes from the two species were morphologically quite similar, each consisting of a short head, neck and tail. The head included a conic, corkscrew‐shaped, bilayered acrosome and a cylindrical nucleus with condensed chromatin. The nucleus is surrounded by cytoplasm organized in ovoid elements with an electron‐dense core. The neck is very simple, containing a centriole and unmodified mitochondria. The flagellum contains a 9+2 axoneme and terminates in a tuft of between eight and 10 microtubules. The spermatozoa ofAmphibolus, like those of the other eutardigrades, are of the modified type, but nonetheless maintain some primitive aspects of the gametes from heterotardigra

ISSN:0001-7272    

DOI:10.1111/j.1463-6395.1995.tb00991.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY