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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    apparent, and the peripheral portion of the cytoplasm tends to be free from vacuoles. In Dasyurus the formation of these deutoplasmic vacuoles begins in oocytes about ’2 mm. or less in diameter. This characteristic pseudo-alveolar ” stage is followed in both Vesperugo and Dasyurus by one in which there is recognisable in the cytoplasmic body of the ovum a differentiation into a dense peripheral zone and a central vacuolated area. In Vesperugo this stage is attained about the time of appearance of the first polar spindle, whilst in Dasyurus it is attained somewhat earlier, always prior to the formation of the latter. So close is the agreement between the two forms that Van der Stricht’s desci’iption of the bat’s egg at the time of appearance of the first polar spindle might equally well be applied to the full-grown ovum of Dasyurus. He writes [’03, p. 43] : “Vers I’epoque de I’apparition du premier fuseau de maturation, le vitellus prend un autre aspect. La partie centrale deutoplasmique conserve une structure pseudo-alveolaire, mais dans le voisinage immediat du premier fuseau et daus toute I’etendue de la couche peripherique du protoplasme, apparait une mince zone de vitellus compact et dense, plus ou moins homogene ou les vesicules claii’es font defaut. . . . A ce moment, on distingue daus I’odcyte de V. noctula une zone centi’ale tres etendue, riche en deutoplasme et une zone corticale tres mince, riche en vitellus plastique.” This centro- lecithal phase, as we may term it, is followed in Vesperugo during fertilisation and the separation of the second polar body by a telolecithal phase characterised by a distinct polarity. “ La zone de vitellus plastique s’epaissit encore, mais surtout a un pole de I’oeuf, a celui oppose au pole ou se detachent les deux globules polaires. Ce pole, ou s’accumule graduellement le vitellus formateur, merite le nom de pole animal. II est oppose au pole d’expulsion des globules polaires, vers lequel est refoule le deutoplasme, et qui se comporte desormais comme le pole vegetatif. Pendant que les deux pronucleus male et femelle se ferment, le vitellus plastique augmente graduellement en abundance au pole