摘要:

The retina of a 32‐7 cmProtopterus aethiopicuswas fixed in glutaraldehyde and osmium tetroxide. Araldite‐embedded sections were examined by optical and electron microscopy. A cell of the inner nuclear layer was found undergoing mitosis, but it is not possible to say to which class this cell belongs. The normal pattern of retinal cell division in developing and postlarval fish and amphibians is discussed; in neither is mitosis in the inner nuclear layer usual. Retinal regeneration after injury occurs in urodele amphibians, with which lungfish have close affinit

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1970.tb00726.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

Previously published accounts of the syncranium ofPantodon buchholziare conflicting and an investigation of extensive material showed them all to be either incomplete or inaccurate. The syncranium is therefore redescribed and a comparison made with the earlier descriptions.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1970.tb00727.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The dentition of the American opossum,Didelphis marsupialis, has been examined using prepared skulls, occlusal casts and, during normal function in chewing, by cinefluorography. The information obtained from these studies has been used in a simulation of the power stroke of mastication on a stereotaxic machine. The directions and amplitudes of the movements used in chewing have been demonstrated.Two types of power stroke are described; a crushing‐puncturing stroke associated with tooth‐food‐tooth contact occurring in the early stages of mastication, and a shearing stroke with tooth‐tooth contact occurring later. The first type produces a rapid flattening of the tips of the cusps, the second a series of striated wear facets on the slopes of the cusps. In the shearing stroke the food is triturated by an anteromedial movement of the paracristid of the lower molars across the metacrista of the upper. Active chewing occurs on one side of the mouth only at any one time and for a considerable number of cycles. The symphysis does not cross the midline during any sequence of cycles. The anteromedially directed power stroke is mediated in part by the mobile symphysis which allows asymmetrical movement of the two dentaries and by a Bennett shift of the mandibular condyles.The similarity between the molars ofDidelphisand those of the early therians, notablyAlphadon, PappotheriumandHoloclemensiais recognized. It is suggested that the information obtained from this study may assist in the interpretation of early therian

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1970.tb00728.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

摘要:

The function of the reproductive accessory glands has not before been investigated. Their prominence arouses interest in their possible function. A preliminary histological, histochemical, and biochemical analysis has been undertaken in order to start to answer this question. No definite conclusions can, however, be made from the results obtained. From evidence accumulated on the behaviour of the sexes and the peaks of secretion production it seems likely that the product of the female glands would be used to coat the eggs with a colleterial substance. The male Geophilomorpha, Scolopendromorpha, and Lithobiomorpha all spin webs on which they place a spermatophore during courtship, and all three groups possess two well developed pairs of accessory glands which may be responsible for the production of web material. The Scutigeromorpha, on the other hand, only possess a single vestigeal pair of glands and do not spin a web. It is suggested that the accessory glands of the male produce web material although this still remains unproven.

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1970.tb00729.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY

ISSN:0024-4082    

DOI:10.1111/j.1096-3642.1970.tb00726a.x

出版商:Blackwell Publishing Ltd    

年代:1970

数据来源: WILEY