The early development of the marsupialia, with special reference to the native cat (dasyurus viverrinus) / by J.P. Hill.

  • Hill, J. P.
Date:
[1910?]
Catalogue details

Licence: In copyright

Credit: The early development of the marsupialia, with special reference to the native cat (dasyurus viverrinus) / by J.P. Hill. Source: Wellcome Collection.

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    early stages (ranging from the 4-celled stage to the completed blastocyst), on whose examination Selenka based his account of germ-layer formation in Didelphys, would thus appear to have been derived from a single female.^ No wonder it is impossible to reconcile his description either with what we know of germ-layer formation in the Prototheria and Eutheria or with my account of the same in Dasyurus. My own experience with the latter has shown me that no reliance whatever is to be placed on segmenting eggs or blastocysts which exhibit marked retardation in tbeir stage of development as compared with others from the same uterus, and also that batches of eggs or blastocysts in which there is marked variation in the stage of development attained should likewise be rejected. Abnormalities in the process of cleavage and of blastocyst formation are by no means un- common in Dasyurus, and during the earlier stages of my own work I spent much time and labour on the investigation of just such abnormal material as that on which Selenka, no doubt unwittingly, but I feel bound to add, with an utter disregard for caution, based his account of the early develop- ment of Didelphys. I propose now, before passing to my own observations, to give a short critical account of Selenka’s observations, my comments being enclosed in square brackets. The uterine ovum of Didelphys is enclosed by (1) a rela- tively thin “ granulosamembran,” formed by the transforma- tion of a layer of follicular cells [really the shell-membrane, first coiTectly interpreted by Caldwell C87) and formed in the Fallopian tube] ; (2) a laminated hiyer of albumen, semitrans- parent ; (3) a zona radiata, not always recognisable [in my experience invariably distinct]. Cleavage begins in the uterus, is holoblastic, and at first equal. A 2-celled stage is figured (Taf. xvii, fig. 3) [not quite normal as regards the relations of the blastomeres], and also a 4-celled stage [normal in appearance except for the * The collection of my own early material of Dasyurus has involved the slaughter of over seven dozen females.