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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    rently did not regard the “ urentodermzelle ” as the sole progenitor of the entoderm, but simply as an entoderm-cell precociously inturned from the blastoporic ” margin. This view of Selenka, however, lands us in the predicament of having to regal’d the embryonal area as differentiating over the vegetative hemisphere, since in the next stage the ‘'blastopore^’ is described as being situated excentrically in that ai’ea. Either Selenka’s detei’mination of the poles in the 42-celled blastocyst is wrong, or the entoderm does not originate as he describes it. My own observations force me to accept the latter alternative. In his paper Selenka gets over the difficulty very easily by altering the orientation of his figures. On Taf. xvii, the figures of sections of blasto- cysts are so placed that the “blastopore ” is below, next the bottom of the plate. These figures I hold to be correctly orientated. On Taf. xviii, the figui’es are inverted, so that the “blastopore” is above; as the result the animal pole of fig. 11, Taf. xvii, becomes the' vegetative pole of the stage next described (fig. 2, Taf. xviii).] The stage just referred to, described as an “eiformige gastrula,” is represented in a drawing made from the fresh specimen as lying quite free in a large perivitelline space enclosed by a very thick layer of albumen, outside which is the “ granulosa-membran.” In section (fig. 2) a mass of entoderm is seen to reach the sm-face at one pole (marked hi.) uppermost in the figure, whilst other entodermal cells are shown spreading from this towards the lower pole. The ectoderm of the wall is represented as composed of definitely cubical cells. [The presence of a large perivitelline space, by itself stamps this specimen as not normal. The sectional figure must be schematic.] The last of Selenka’s early stages to which reference need be made here is formed by eight “ gastrulas” (blastocysts), reckoned as ten hours after the commencement of cleavage [a reckoning I consider of no value] (Taf. xviii, figs. 3 and 4). The embryonal area is now distinguishable by the larger size of its ectodermal cells. The entoderm is unilamiuar, and has