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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    extended beyond the limits of the embryonal area. The position of the “ blastopore ” is said to be marked in all by a mass of coag’ulum attached to the wall, and in three by a definite opening' as well. It is situated excentrically in the embryonal area. [Except for the ‘‘ blastopore and the presence of a thick layer of albumen, this blastocyst stage is quite comparable with the corresponding one in Dasyurus; the latter, however, is considerably larger. Of Selenka’s early material, I think it is these blastocysts alone which had any chance of giving origin to normal embryos.] W. H. Caldwell, who, as Balfour student, visited Australia in 1883-4, obtained a very rich collection of early marsupial Tnaterial, of which, unfortunately, no adequate account has ever been published. He gave, however, in his introductory paper on the ‘ Embryology of the Monotremata and Marsu- pialia^ (^87), an account of the structure of the ovum, both ovarian and uterine, in Phascolarctus, and he showed that the ovum during its passage down the Fallopian tube becomes enclosed outside the albumen layer in “a. thin transparent membrane, ’0015 mm. thick,” which he homologised with the shell-membrane of the monotreme egg. This impoi*tant dis- covery of the existence of a shell-membrane in the Marsu- pialia I can fully confirm. I am, however, unable to accept his interpretation of the internal structure of the ovum of Phascolarctus, or his remarkable statement that cleavage in that form is of the meroblastic type. Cleavage is not described in detail, nor is any account given of the mode of origin of the germ-layers. Chaptee JI.—The Ovum op Dasyueus. 1. Structure of the Ovarian Ovum. The full-grown ovarian ovum of Dasyurus (PI. 1, fig. 1) appears as a rounded, or more usually, ovalish cell, the diameter of which varies in section in ten eggs measured from '28 X ‘126 mm. to '27 x '26 mm. (average, ’24 mm.), and is therefore large relatively to the ova of Eutheria. It