ISSN:0373-4137    

DOI:10.1080/11250006209440614

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor

摘要:

A comparative study of the parthienogenetic and amphigonic egg development of Aphids, has shown & clear resemblance between some aspects of the two maturative processes. In the amphigonie egg bivalents become indistinet soon after the stage of highest contraction. In the parthenogenetie egg however the bivalents the stae of highest contraction. In the parthenogenetie egg however the bivalents separate and the diploid number of chromosomes is restored within the nuelear membrane. The second maturative division originates, in the partheogenetic egg a single diploid polar body. In the amphigoni egg the emission of two aploid polar bodies occurs in the normal way. In both ovogenetic processes the bivalents reach threfore the highest contraction stage before the «resting» stage. A delay in the beginning of the resting stage of the nucleus is shown therefore in the egg maturation of Aphids, which is not shown in most other Inscets orders. Such peeculiar behaiour of the chromosomes of the amphigonic egg of Aphids has probably permitted the establishment of endomeiosis in the parthenogenetie infividuals and consequently has brought about the genetie variability found in single parthenogenetic lines of Aphids. 30 parthenogenetic femals have been bred in two thermostats: 15 of them at a temperature of 18°C and 15 at 28°C, Light intensity. moisture and food supplies were kept constantly identieal in both thermostats. The eytological study of the embryos demostrated that endomeiosis occurs in the female individuals kept at 18°C and at 28°C normally ameiotie parthenogenesis occurs. Temperature influences therefore endomeiosis. This is the reason why meiotic stages in the maturation of Aphid's parthenogenetic eggs have been only irregularly observed by previous Authors. The presence of endomeiosis in a few embryos in individuals bred at 28°C shows on the other hand the existence of genotypes with favour endomeiosis in spite of the high temperature.

ISSN:0373-4137    

DOI:10.1080/11250006209440615

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor

摘要:

The author summarizes the endocrinological aspects of reproduction in the bony and eartilaginous fishes, in the light of the most recent obsevations. The enormous number of species which constitue the superelass Pisces together with the extensive variety of modes of reproduction reader sehematization of the complex endoerine correlations most difficult.

ISSN:0373-4137    

DOI:10.1080/11250006209440616

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor

摘要:

In a panmictic population inbreeding induccs fixation of alleles in a homozygous state, and favours the eliminations, through natural selection, of those alleles which have any selcctive disadvantage, Thus inbreeding tends to reduce the genetic variability of a population. Another effect which comes from inbreeding is given by a differentiation of groups within the population, and of populations within the species, without the requirment of geographie barriers-and the presence of intermediate populations.

ISSN:0373-4137    

DOI:10.1080/11250006209440617

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor

ISSN:0373-4137    

DOI:10.1080/11250006209440618

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor

ISSN:0373-4137    

DOI:10.1080/11250006209440619

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor

ISSN:0373-4137    

DOI:10.1080/11250006209440620

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor

ISSN:0373-4137    

DOI:10.1080/11250006209440621

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor

ISSN:0373-4137    

DOI:10.1080/11250006209440622

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor

ISSN:0373-4137    

DOI:10.1080/11250006209440623

出版商:Taylor & Francis Group    

年代:1962

数据来源: Taylor