摘要:

Oogenesis and oocyte envelope differentiation were examined in the viviparousBotrylloides violaceus, a compound ascidian producing small alecithal eggs about 80 μm in diameter. Oogenesis was divided into five stages, defined according to ultrastructural changes in envelopes and oocyte growth. In the gonadal blastema of young buds, each oocyte in the early meiotic prophase is partially enveloped by a few primary follicle cells (stage I) which adhere to the oolemma at several junctional points. In stages II and III, these cells give rise to an external continuous layer (presumptive outer follicle cells) and to underlying scattered elements which later differentiate into test cells and inner follicle cells (stage IV). The direct contribution of mesenchymatous elements was not observed in inner follicle cells and test cells. Observations on the time of appearance and development of organelles, microvilli and endocytotic activity in growing oocytes are reported. Oocytes progressively accumulate “clear” vesicles containing a loose mat and small spherical bodies resembling the previtellogenic bodies observed in other botryllids; they are seen to receive contributions from Golgian vesicles. However, the typical electron-dense yolk globules described in the oocytes of ascidians so far examined were never observed. The meaning of these clear vesicles and the possible role of envelopes in oocyte development are discussed, and the small alecithal eggs ofB. violaceusare compared with the yolky eggs of other ascidians.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672447

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Sperm of the paludicolan tricladRomankenkius libidinosusconsist of a distal process and a main body, and of two free flagella arising from the zone between both. Flagella are fused for a short distance and their tips are split into long “microvilli” containing microtubules. The single long mitochondrion extends from the distal process to close to the tip of the main body. The nucleus, consisting of lucent and dense components coiled screw-like around each other, does not extend into the distal process. A peripheral row of microtubules consists of about 37–39 microtubules in the middle parts of sperm, decreasing towards both ends. A short row of three inner microtubules extends along most of the main sperm body. Surface ornamentations are present at both ends but not in the middle parts. In early spermatids, joined by cytophores, a row of microtubules forms beneath the plasma membrane in the zone of differentiation and close to it an intercentriolar body with several dense bands connected by filaments. Many nuclear pores are prominent in the region of the nucleus close to the zone of differentiation, and an apical layer of dense nucleoplasm develops. Two flagella appear, facing in opposite directions and then rotating to lie parallel with each other. Rotation is probably brought about by contraction of microtubules inserted in the basal bodies and “dense plates” around them. Striated rootlets (“basal complexes”) between basal bodies and the nucleus may support the flagella during rotation. The intercentriolar body splits into two, each half remaining at the base of a basal body, but parts of the central band are left behind. A cytoplasmic process grows out, the mitochondria fuse, and the nucleus elongates. In outgrowing spermatids, inner microtubules are not present. An unidentified maricolan triclad has similar sperm and spermiogenesis. Triclads resemble other platyhelminths in a number of characteristics of sperm and spermiogenesis, but ultrastructure of sperm and spermiogenesis does not permit a conclusion as to whether they are more closely related to the proseriates or rhabdocoels.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672448

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Histological observations on the sea anemoneHaliplanella lineata (=H. luciae) from the Miura district of Japan revealed that the sexes are separate, and in the male changes in testicular structure and spermatogenesis are seasonal. Spawning occurred in summer (July and August). Testicular structure has the form of numerous cysts, located within the mesoglea of the mesenteries. The first phase of spermatogenesis was found in the mesenterial epithelium. From the gross features of the cysts and spermatogenesis, the process of maturation in testicular structure was divided into four stages: recruiting stage, growing stage, mature stage, and regressing stage. The sexual reproduction observed was contrasted with the asexual propagation by pedal laceration reported from northern Japan.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672449

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

InCodakia orbicularis, the spermatozoon has a short cylindrical acrosome separated from a long, curved, tapered nucleus by a large subacrosomal region. The cinetic apparatus is made of a complex system of fibrillar processes linking the distal centriolar satellite bodies to a microtubule-like ring which, in turn, is anchored to the plasma membrane through a fibrillar network issued from the secondary satellites at the basal part of the middle-piece where it is encased in a circular flange. The tail contains a normal axonemal pattern; moreover, a large undulating membrane, oriented in the same plane as the central microtubules, is differentiated along the flagellum. The elongated nucleus together with the differentiation of the middle piece and tail represent a significant modification of the primitive type of spermatozoon.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672450

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Vitellogenin of the desert locustSchistocerca gregariawas purified from haemolymph of ovariectomized females. The native Vg preparation was homogenous as judged by PAGE and immunodiffusion. It has a molecular mass of 610 kDa and is composed of five polypeptides as demonstrated by SDS-PAGE. Sg-Vg precipitates at low ionic strength. Vg concentration in the haemolymph of maturing females was determined with an ELISA and found to reach maximum values of 30 mglml. The antiserum against Sg-Vg crossreacts with Lom-Vg. The optimum conditions forin vitrouptake of Vg byS. gregariaoocytes were determined. No phase differences were observed in uptake of Sg-Vg.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672451

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper reports on the reproductive behavior of gametogenically active polyps ofHydra vulgaris(Pallas, 1766) strain “Scotland 1989” covering an observation period of 4 years (1989–93). The monitored sexually active hermaphrodites and all their asexually generated offspring produced gametes in uninterrupted series of individual sexual periods, which did not exclude reproduction by budding. Quantitative data are given about the investments made by polyps into gametogenesis in the course of a sexual period. A growing oocyte incorporates more than 10,000 nurse cells (interstitial cells) into the ooplasm by phagocytosis. Various observations suggest that male and female gametes derive independently from separate predetermined stocks of stem cells which are autonomous in their turn from the cell populations committed to somatic renewal processes. Only a small number of the fast and slow developing embryos survived a critical post-hatching period.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672452

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The ontogeny of the eyestalk neuroendocrine centers of the European lobster,Homarus gammarus, throughout embryonic development has been studied using light and electron microscopy, and the localization of specific neuroendocrine substances has been identified by immunocytochemistry. The procephalic lobes, which are the prospective eyestalks, develop progressively during embryonic development. In the nauplius stage two neuron masses are well defined. The visual structure originates from one of them and the neuroendocrine structure from the other. The four definitive optic ganglia are present at the mid-metanauplius stage and retain their appearance and location in larvae and adults. The organ of Bellonci, an internal sensory structure, appears at the mid-metanauplius stage and is mainly characterized by onion bodies. The medulla terminalis X-organ complex, an important neuroendocrine system, is present and already functional at the beginning of the embryonic metanauplius stage. Two neurohormones have been visualized immunocytochemically: the crustacean hyperglycemic hormone (CHH) and the gonad inhibiting hormone (GIH). Both neuropeptides are localized in the perikarya of neuroendocrine cells of the X-organ as well as in their tracts joining the presumptive sinus gland. However, the sinus gland has only been observed in the early larval stages just after hatching.

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672453

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672454

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672455

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1995.9672446

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor