摘要:

This paper begins a series aimed at clarifying the structure and function of reproductive organs in Gastrotricha Macrodasyida. Morphological data are presented forDolichodasys carolinensissp.n. andD. delicatussp.n. Both are elongate, have reduced adhesive organs and complex accessory reproductive organs, termed the frontal‐caudal organ system. The system consists of a band of cells behind the gonads in the central body chamber. The anterior portion, the frointal organ, stores foreign spermatozoa; the posterior portion, the caudal organ, may function as a copulatory organ. The caudal organ has two canals forming a loop opening at a single ventral pore. One canal contains a spiralled secretion, the other elongated filaments that appear to be muscle cell derivatives. Systematic groupings are made for other long‐bodied Gastrotricha Macrodasy

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00769.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Laboratory studies on the normally fissiparousDugesia biblicafrom Israel (3n=27+xsupernumeraries) have been made in order to investigate fission rates and spontaneous maturation of four fissioning populations and one clone. Laboratory induced maturation in a sixth population ofD. biblicaresulted in the laying of fertile cocoons, the offspring of which were either 3n=27+x, 2n= 18+xor 2n= 18+xIt is suggested that triploidy is primarily responsible for the lack of sexual reproduction in the field, and that unequal inheritance of supernumerary chromosomes during mitosis may explain the differing tendencies to undergo spontaneous maturation by individuals of a clone ofD. biblica.The karyotype, habitat and reproduction ofD. biblicais compared with a closely related but diploid, normally sexually reproducingDugesiaform and possible relationships between these two are discussed.

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00770.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The exoskeleton ofLimulus polyphemus(L.) (Xiphosura, Merostomata) is described on the basis of scanning electron microscopic (SEM) studies. Three principal layers are distinguished: “epicuticle”, exocuticle, and endocuticle. The exocuticle is composed of horizontal lamellae interconnected by vertical curved lamellae (“parabolic arcs”). Its structure is essentially as that in the exoskeletons of other arthropod groups. The endocuticle consists of vertical lamellae which seem to be homologous to the vertical curved lamellae in the exocuticle. Prior to the molting, most of the endocuticle is dissolved by the animal. Detailed descriptions are given on the structure of the horizontal and vertical lamellae, and on the course of the pore canals. A vertically lamellar, thick endocuticular layer also occurs in the extinct eurypterids. In recent scorpions, a typical development of the vertically lamellar structure is only found in the chela of the pedipalps and in the leg joints. The main part of the exoskeleton has a horizontally lamellar structure, but the horizontal lamellae are often widely spaced—thus the vertical lamellae dominate. The functional significance of the vertically lamellar structure is

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00771.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Decalcified and undecalcified preparations of the crabCancer pagurusin the intermoult condition were studied to examine the mineralization and structure of the epicuticle, using light microscopic, electron microscopic, and microradiographic methods. The epicuticle was found to be composed of two layers, one superficial membrane, and one thicker layer, measuring 1‐2 μm. From the base layer spines or microtrichia projected. These were approximately 18 μm long and built like the remainder of the epicuticle. The spines and the base layer of the epicuticle contained vertical canals which in undecalcified sections accomodated columns of crystals. These canals were the only location in which minerals occurred in the epicuticle. In decalcified preparations filamentous strands were observed in the canals. Elsewhere in the epicuticular tissue no fibrillar structure was observed. The canals and their contents seemed to extend across the junctional zone between the epicuticle and the exocuti

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00772.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

The peculiar habitus of Amphipods with lateral compression, deep coxal plates 1‐4, broad bases of peraeopods 5‐7, and enlarged pleura (epimeral plates) of abdominal segments 1‐3 is seen as a functional system closely dependent upon the currents produced by the incessant beating of the pleopods. The derivation and position of branchiae and oostegites is discussed. The morphology of more or less aberrant groups, including the suborders Caprellidea and Ingolfiellidea, and its correlations with the mode of life and the basic functional model is analyzed. The possible bearing of the functional model system upon the position of the Amphipoda among the Peracarida is briefly dealt

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00773.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

Amphyllodomus incurvariagen. et sp.n. is described and figured. The species lives among hydroids and algae and has a remarkable domiciliary biology in that it carries around a house built of two oval pieces of brown algae cut out by the animal itself. The species is placed in the Amphithoidae, but certain deviations from that family place it in an isolated position.

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00774.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

A description is given of the caudal skeleton inLepisosteusfounded on two specimens ofL. osseus(L.) and figures and sketches of other species of the genus. A comparison is made with caudal skeletons of the Mesozoic generaIonoscopus, Oligopleurus, UroclesandCaturusand the RecentAmia.They are all referred to a polyural type in a wider sense, different in principle from the diural type, characteristic of primitive living teleosts. A polyural caudal skeleton from the U. Jurassic of Cerin, France, is described; its identification with one of the known species from this locality is not possible.

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00775.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

A study of the origin and development of the bony complex (“dentaire” s.l.) later forming the anterior part of the mandible ofSalmo farioleads to the following conclusions: (1) various modes of ossifications occur in the ontogeny of this bony complex, (2) the main component is the dermal (dento‐splénial) whereas the enchondral one (mentomeckelien) is much reduced, (3) the proposed term “dento‐splénio‐mentomeckelien” focuses attention, at the same time, on the order of appearance and relative importance of the

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00776.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

A new, monotypic, genus is proposed for the fish hitherto known asApistogramma ramireziMyers&Harry, 1948. It is probably related toGeophagusHeckeland BiotodomaEigenmann&Kennedy. It differs considerably in behaviour and morphology from other species assigned to the genusApistogrammaRegan, to which it is considered to be not very closely related.

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00777.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY

摘要:

(1) The individuals in the densely populated stock of brown trout,Salmo truttaL., living in Lake Lane and Stranda River, are small, mature at an early age, and have a relatively short life span. Such a demographic strategy appears favourable for populations having a large, but physically unstable spawning and nursery area, intense competition for food, and little vertebrate predation except for human exploitation. (2) For females, the age of sexual maturation appears largely dependent on growth‐rate, size, and survival‐rate of the fish. Males do not appear to have the advantage of a corresponding large body size. They mature when smaller and at more varying ages than the females, although the two sexes have almost identical growth‐rates. (3) Sexually mature fish have higher condition coefficients than immature ones, which is probably an adaptation to ensure gonadal development and enhance the prospect of reproductive success. (4) Mortality appears to be largely dependent on the age when the fish achieve sexual maturation. Most individuals seem to die after their first spawning season. Females show a delay of one year in their sexual maturation relative to males. This adaptation gives protection to the fe

ISSN:0300-3256    

DOI:10.1111/j.1463-6409.1978.tb00778.x

出版商:Blackwell Publishing Ltd    

年代:1978

数据来源: WILEY