摘要:

We studied the structure of the walls of the central gonadal duct inLimnadia lenticularis, the structures responsible for eggshell formation. The longitudinal duct wall is made of a single layer of somatic glandular cells, mixed with female germ cells. The material forming up the shell was produced within a system of vesicles derived from the nuclear membrane and then transported to the lumen's surface and released in the form of drop-like secretions that came together gradually in a mass that would eventually fill the gonad. We then studied eggshell maturation in newly spawned and mature eggs and observed it through its various transformations until they reached their definitive shape, that of so-called “twisted” eggs. We compared data on ultrastructure, obtained from comparison of the eggshell inLimnadiawith those from other Branchiopods asTriopsand the Leptestheriidae, and from the results we concluded that eggshell resistance in the Branchiopods we observed is correlated to the species reproductive strategies.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652395

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The structure and function of the posterior vas deferens (PVD) of the male snow crab,Chionoecetes opilio, were studied by light and electron (SEM/TEM) microscopy. The vas deferens is divided into three regions: anterior (AVD), median (MVD) and posterior (PVD). Spermatophores are formed in the AVD and moved to the MVD where they are stored within droplets of seminal fluid. Seminal fluid and spermatophores are strongly PAS positive. The reaction with alcian blue-PAS indicated the presence of neutral polysaccharides. The PVD is further divided into the distal and proximal regions that differ in structure and function. In the distal region of the PVD, the epithelial cells are columnar containing lobed nuclei. The lumen contains a mixture of lysed spermatozoa and spermatophores. Numerous heterophagic vacuoles present at the cell surface are absorbed and digested intracellularly. The cytoplasm contains a large amount of rough endoplasmic reticulum and lysosomes associated with Golgi complexes and few mitochondria. TEM observations reveal that the primary function of this region is the phagocytosis of excess spermatozoa. The digestive function of the distal region of the PVD suggests that this mode of secretion is apocrine. The proximal region of the PVD contains neither spermatophores nor free spermatozoa. The epithelium is composed of cuboidal cells with elongate nuclei. The apical microvilli are short and regularly arranged. The lumen contains a large quantity of an amorphous, jelly-like substance, which is the secretory product of the distal region of the PVD. In the cytoplasm rough endoplasmic reticulum and Golgi complexes are absent. We conclude that the proximal region of the PVD, therefore, is used for storage of highly acidic seminal fluid. The function of the PVD for the destruction and resorption of spermatophores and spermatozoa has not previously been reported in other decapods.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652396

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

We studied the maturative pattern of the ovotestis and the reproductive cycle of two hermaphrodite species of eutardigrades belonging to different families and collected independently from a chestnut litter. A long-term study onMacrobiotus joannae(Macrobiotidae), collected monthly, and a short-term study onAmphibolus weglarskae(Eohypsibiidae) were carried out. In both species the reproductive apparatus is represented by an ovotestis and by a short gonoduct., A caudal sack-like evagination of the ovotestis was found only inM. joannae.The size of the gonad varied in relation to the body size and degree of maturation of the germinal elements. In both species the maturative pattern of the ovotestis can be subdivided into four stages. The first stage includes three phases (undifferentiated, male and previtellogenic phases), whereas stages 2–4 correspond to the stages of vitellogenesis. Groups of 3–8 oocytes mature in strict relation to the molting cycle. In both species there are at least two cycles of egg production, indicating that hermaphroditic tardigrades are iteroparous. Apart from the first two phases of stage 1, all stages simultaneously possess male and female germinal elements which are not separated by barriers. The gonad is exclusively male only in relatively small specimens of both species, indicating that the male phase (m) is present only in the first reproductive cycle. The contemporary presence of mature oocytes and spermatozoa in close contact with each other is evidence that tardigrades are simultaneous hermaphrodites, and it suggests the existence of self-fertilization. This conclusion allows us to view our results in the light of predictions from current theories on sex energy allocation in hermaphrodite and gonochoristic tardigrades. Lastly, we compared the reproductive cycle of these two hermaphroditic species and those of a gonochoristic species belonging to the same genera.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652397

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The enchytraeid oligochaeteEnchytraeus japonensisreproduces asexually by fragmentation under laboratory conditions. In the fragmentation process, fully-grown worms break into several fragments. Each fragment regenerates into a small but complete worm in 4 days, grows rapidly and divides again in another 10 days. We found that this fragmentation can be induced artificially by amputating the head if the worms are at least 5–6 mm in length, but not in shorter worms. The fragmentation is inducible by removing the most anterior two segments, if the worms are large enough. When a worm is cut into two, fragmentation occurs more readily in the posterior section. Moreover, even a small incision made in the ventral side of the trunk causes fragmentation in the body posterior to the incision. Immersion of the worms in water is found to inhibit fragmentation even in decapitated worms. When a worm is placed in water immediately after decapitation, the ability to fragment is gradually lost as a new head regenerates. From these results it is postulated that the ability to fragment acquired early in the growth phase is suppressed by head-derived signal(s) until spontaneous fragmentation occurs. The signals seem to be constantly transmitted through the ventral nerve cord until the head matures and lifts its blockade of fragmentation, allowing this process to proceed. At present, however, we cannot exclude the possibility that the mature head of the worm produces fragmentation-stimulating signals.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652398

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Four regular zoeal, the megalopal and first two crab stages ofLopholithodes mandtiiBrandt were reared under laboratory conditions. Additionally one specimen passed through a fifth zoeal stage. All stages are described and illustrated.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652399

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Our previous study failed to show vitellin synthesis in the ovary of the prawnMacrobrachium rosenbergii(Sagi et al., 1995); thus the role of the hepatopancreas as a possible site of synthesis was evaluated. Extracts of hepatopancreas and hemolymph of a secondary-vitellogenic female exhibited higher levels of yolk protein than those from a primary-vitellogenic female. Clear vitellin immuno-cross-reactivity was observed in hepatopancreas sections from a secondary-vitellogenic female while no such reaction was found in a male hepatopancreas. Furthermore, vitellin-immuno-cross-reactive polypeptides released into the culture medium of the hepatopancreas of a secondary-vitellogenic female were similar to those found in the hemolymph and ovary (92 and 105kDa). The most prominent immuno-reactive polypeptide in the hepatopancreas extract was a relatively low-molecular-weight species (42kDa).De novosynthesis of cross-reactive-vitellin polypeptides (34, 38 and 42kDa) was detected in the hepatopancreas of a secondary-vitellogenic female. Synthesis of these polypeptides were not detected in the secondary-vitellogenic ovary or in the male hepatopancreas. The appearance of similar polypeptides following incubation of a secondary-vitellogenic ovarian extract with a glycosidase suggests that these polypeptides could be subunits of a core protein of vitellogenin, which was synthesized in the hepatopancreas and then released to the hemolymph following post-translational modifications. Our findings thus suggest the hepatopancreas to be a likely site of synthesis of a yolk protein precursor inM. rosenbergii.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652400

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Temporal and spatial expression of embryonic alkaline phosphatase (ALP) activity in the oligochaeteTubifex hattaiwas examined by means of histochemical staining. During the course of development up to 7 days (at 22°C), ALP activity emerged in three distinct structures in the following order: dorsal surface linear structures running along the midline, nephridium-like structures located in the mesodermal territory of segments 7 and 8, and ventral vessels located in the space between ventral ganglia and the endoderm. Stage-by-stage observation showed that the dorsal linear structures originate as a bilateral pair of small cell clusters that appear at the anterior end of the early gastrula embryo. Likewise, each nephridium-like structure was traced back to a single ALP-positive cell that emerges at the ventrolateral region in each of segments 7 and 8 at the late gastrula stage. Ventral vessels became ALP-positive, first in segments 5–13 and then in more posterior segments. No ALP activity was detected in the endoderm during embryogenesis.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652401

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Ovarian development in the red claw crayfishCherax quadricarinatusis divided into two major phases, namely primary- and secondary-vitellogenesis. Two anatomically distinctive types of primary-vitellogenic ovary are present: one contains uniform milky white oocytes (in the chromatin, chromatin-nucleolus, early-perinuclear and late-perinuclear stages), while the other contains two diversely colored oocyte populations, the smallest oocytes being uniform milky white and the largest being yellow to orange (i.e., at the lipid stage). Secondary-vitellogenic ovaries are characterized by the presence of a synchronously growing large oocyte group together with oocytes of all the first four, primary-vitellogenic stages. The synchronous group develops from the yolk stage via the prematuration stage into the maturation stage. Polypeptides of relatively low molecular masses (65–95 kDa) are abundant in the primary-vitellogenic ovary containing chromatin to lipid-stage oocytes. Polypeptides of relatively higher molecular masses (<100kDa) were detected both in the secondary-vitellogenic ovary (composed mainly of yolk-stage oocytes) and in newly laid eggs. During secondary vitellogenesis, the high-density lipoprotein (HDL) fraction of the hemolymph contains four secondary vitellogenic-specific polypeptides (208, 196, 177 and 80 kDa) that are not present in the hemolymph of the primary vitellogenic female. In this study we have elucidated the relationship between the progress of gonad maturation, oocyte development and the sequence of appearance of specific polypeptides in the ovary and the hemolymph ofC. quadricarinatus.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652402

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Primordial germ cells (PGCs) from embryos of the giant freshwater prawn,Macrobrachium rosenbergii, are remarkably large with granulated cytoplasm. The prominent nucleus contains several conspicuous nucleoli. The 5.5–6.5-day-old embryos are good sources for PGC isolation since they contain a relatively high proportion of the PGCs and the embryonic cells at these stages are easily dissociated. Embryos 5.5–6.5 days old and 14.5–16.5 days old were homogenized, and the cell suspensions were either mechanically or enzymatically dissociated. The dissociated cell suspensions were fractionated in the three-layered Percoll discontinuous gradient. An average of 38.8±5.8% and 27.5±4.4% PGCs were obtained at the interface between 25% and 30% and between 30% and 35% Percoll, respectively, following mechanical dissociation of cells of 5.5–6.5-day-old embryos.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652403

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The acrosome reaction inStyela plicataspermatozoa occurs through vesiculation in which a vesicle bounded by a hybrid membrane, formed from the acrosomal membrane and the overlying plasma membrane, is generated as a byproduct. The head of the spermatozoon ofS. plicatais about 6 μm long. In the apex of the head an acrosome is present, which appears as a flattened vesicle (about 150x 150x50 nm). The apical part of the acrosomal membrane and the overlying plasma membrane are in close contact with each other. The acrosome reaction appears to involve the fusion of the acrosomal membrane and the overlying plasma membrane along the marginal region of the acrosomal vesicle. Membrane fusion results in the formation of a vesicle bounded by hybrid membranes of the acrosomal membrane and the overlying plasma membrane, which eventually detaches from the tip of the sperm head.

ISSN:0792-4259    

DOI:10.1080/07924259.2000.9652404

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor