摘要:

The development ofHaminaea naviculawas studied by anatomical and histological methods. This species shows typical spiral cleavage, which leads to a stereoblastula. Gastrulation is reached by epiboly. A fully developed veliger larva is reached within the egg capsule that is not only capable of swimming when artificially hatched but is also provided with the same larval organs (larval shell, velum, operculum, larval cephalic sensory organ, anal cells, anal gland, nephrocyst-protonephridial complex, epipodial and pallial gland cells) that are present in pelagic larvae of related species. Aspects of the development ofH. naviculaare compared with observations of the pelagic larvae ofH. exiguaandH. vesicula.Additional data from the literature are discussed.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672610

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Spermiogenesis and the spermatozoa found in the testes of the protandric “turbellarian” parasiteUrastoma cyprinaewere investigated by transmission electron microscopy. The most significant discovery was that spermatids produce two free flagella, the basal bodies of which remain proximal and which fuse in a proximo-distal manner with a median cytoplasmic process. This type of spermiogenesis has previously been found only in neodermatan platyhelminths, and these findings suggest thatUrastomamay be part of the lineage leading to the major parasitic flatworm taxa (Neodermata). They also substantiate earlier suggestions thatUrastomadoes not belong to the Prolecithophora. The mature sperm has cortical microtubules throughout the long filiform body and a spiralling, corkscrew-like proximal region with this end of the nucleus enclosed by cytoplasmic ridges lined with microtubules. At the distal end of this proximal region, the slightly narrowed nucleus continues, flanked by two incorporated axonemes and usually two profiles of elongate mitochondria. After nucleus, mitochondria and axonemes terminate, the distal end contains only microtubules.Kronborgia isopodicola(Fecampiida), previously shown to also have proximo-distal development during spermiogenesis (without fusion with a median cytoplasmic process), may belong to the same lineage. The three taxa (Neodermata,UrastomaandKronborgia) also lack the dense bodies found in the sperm of most “turbellarian” taxa, and have in common a protonephridial flame bulb architecture involving two cells, with filtration ribs unsupported by microtubules.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672611

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Eyestalk ablation at particular times during the second (2 and 20 h post-hatching) and third (10 h intervals up to 70 h) larval instars was studied with regard to effects on instar duration and mortality in the snapping shrimp,Alpheus heterochaelis.Ecdyses and deaths were monitored at hourly intervals during instar 2, every 2 h for instar 3, and at 4-h intervals for subsequent instars up to instar 6. Eyestalk ablation near the end of an instar resulted in increased mortality relative to larvae ablated earlier in the molting cycle. The second instar was lengthened by eyestalk removal during instar 2, while subsequent instars were accelerated significantly (up to 29%). Ablations during instar 3 did not significantly alter duration of that instar, but the next instar was significantly shorter (up to 18%). It was concluded that the Y-organ requires a full instar before becoming effective in shortening instar duration after release stom control by “molt-inhibiting hormone” (MIH) produced by the X-organ within the eyestalk.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672612

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An RIA procedure for assaying a large number of samples in a relatively short time has been developed. It utilizes multi-channel repeater pipettors for the addition of reagents, specially designed racks which accommodate 48 6 x 50-mm tubes and which fit directly into the centrifuge, multitube vortexers, and a specially designed aspiration device. The racks allow the tubes to remain in the same support throughout most of the assay. The aspirator permits the rapid aspiration of eight tubes at a time, 192 in 2 min. One hundred ninety-two samples can be accurately assayed in as little as 2.5 h.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672613

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The embryonic germ cells of sciarid flies normally contain three X-chromosomes, two of which are paternally derived chromosomes. At the final stage of germ band extension, one of the paternally derived X is eliminated from the germ cells regardless of the sex of the embryo. Light microscopy shows that the germ cells, at this stage, are in an atypical interphase exhibiting semi-condensed chromosomes. During chromosome extrusion, one of the smallest chromosomes appears to pass through the nuclear envelope, remaining for some time in the cytoplasm. Fine structural analysis shows that, before elimination, the semi-condensed chromosomes maintain a short distance from the nuclear envelope, except for one chromosome which is attached to the membrane. In this region of the nucleus, there is an accumulation of ribosomes in the outer nuclear membrane and, in the cytoplasm, there is an hypertrophy of the rough endoplasmic reticulum, an accumulation of mitochondria and microfilaments. The internal membrane of the nuclear envelope at the point where the chromosome is attached folds inwards, permeating the chromosome. Later, this nuclear region evaginates forming a long protuberance into the cytoplasm. The stretching of this bulge causes the unfolding of the internal membrane leading the attached chromosome into the interior of the protuberance. This structure finally constricts near the nucleus forming a cytoplasmic vesicle limited by a double membrane and containing the eliminated chromosome. This process takes about 3 h to be completed.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672614

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

It has been established that in the gonochoristic marine planarianSabussowia dioica(Claparède, 1863), the male animal produces sclerotic spermatophores that are deposited onto the body wall of the female. Sperm contained in these capsules penetrate the parenchyma and eventually enter the ovaries and the anterior vitellarian follicles. External deposition of spermatophores is unique within the triclads, while formation of spermatophores is unique within the marine planarians.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672615

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The role of dietary β, β-carotene, β-echinenone, astaxanthin, vitamin A and vitamin E in development of the sea urchinPseudocentrotus depressuswas investigated by feeding experiments. The number of ovulated eggs was 16.3±3.1, 27.5±12.8, 35.7±12.0, 15.1±4.5, 15.9±10.7 and 46.8±15.0 eggs/female (x10−4in control, β, β-carotene, β-echinenone, astaxanthin, vitamin A and vitamin E groups, respectively. Both β-echinenone and vitamin E diets had statistically significant effects on ovulated eggs. Though the rate of fertilization was nearly 100% in all test groups except the vitamin A group, the hatching rate was 66.3, 71.6, 50.8, 37.0, 24.0 and 51.8% in control, β, β-carotene, β-echinenone, astaxanthin, vitamin A and vitamin E group, respectively. The lowest malformation rates were obtained for β, β-carotene and β-echinenone groups. In the case of the control group, the malformation rate was 72% of the total plutei, and the survival rate was only 4.0% from fertilized egg to the 6-armed stage, and that of β, β-carotene, β-echinenone, astaxanthin, vitamin A and vitamin E groups was 14.9, 13.6, 6.0, 6.3 and 8.6%, respectively. β, β-carotene and β-echinenone had significant effects on larval survival. However, the vitamin E diet, which affected the number of ovulated eggs, had no significant effects on larval survival. From the results of the developmental experiments described above, the 9-echinenone group represented the best achievement of all the test groups in both number of ovulated eggs and survival rate. Vitamin A had no effect on either of them. Although a mechanism for these effects cannot yet be identified, the results of this experiment would indicate that carotenoids, especially β-echinenone, exert a major influence on early development.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672616

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The structure of the hyaline spheres (HS) in the larvae of the holothuroidsParastichopus californicusandStichopus japonicuswas examined by electron microscopy, and their sensitivity to a range of hydrolytic enzymes was tested. The HS are attached to epithelium and extend into the blastocoel. They consist primary of extracellular material but scattered cells surround them, and a few are found within matrix. Ultrastructurally, the matrix has a gel-like appearance and contains fine granules and fibrils. HS are dissolved very specifically by hyaluronidase (10 mg/ml, pH 5.4). Pronase, trypsin and papain at the same concentration damage both HS and the larval body to varying degrees. Surprisingly, HS sink when isolated from the larval body, so it is unlikely they serve as flotation devices. It seems more likely they serve as storage of structural elements utilized after metamorphosis.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672617

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Ablation of the osphradium (a peripheral putative chemo-sensory organ) inLymnaea stagnalisresulted in significant increase of egg-laying activity as compared with control animals (observed for 50 days). Cutting the osphradial nerve increased egg-laying to a lesser degree and only for the first 15–20 days. Water changes in the aquaria had a similar stimulating effect on egg-laying activity in both osphradium-deprived and control snails. Permanent aeration of the aquaria abolished this effect. Possible mechanisms of tonic inhibitory action of the osphradium on egg-laying are discussed.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672618

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The structure and setal armature of the mouthparts ofCherax quadricarinatusduring development from juvenile to adult were examined using light and scanning electron microscopy. Significant general transformations include increases in the overall size of the appendages and their component segments or processes, and increases in the number and variety of setal types on the margins and surfaces. Conspicuous transformations that occurred on specific sites of the mouthparts were changes in: (a) the size and shape of third maxilliped and mandibular teeth from canine-like to incisor-shaped or a mixture of somewhat incisor-shaped and canine-like; (b) the setal types replacing other types previously borne on the same site; and (c) the degree of occurrence of the denticulated setae on the 45 mm TL juvenile and adult stages. The implications of these mouthpart transformations on the feeding ability of the early juveniles, late juveniles, and adults are discussed, with mention of the potential ability of the redclaw for suspension feeding. Types of food appropriate for each stage were inferred.

ISSN:0792-4259    

DOI:10.1080/07924259.1997.9672619

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor