16 J. P. HILL. 



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, Avhilst 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 Yan der Stricht's description 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] : "Yers 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 dans toute I'etendue de la couche 

 peripherique du protoplasnie, apparait une mince zone de 

 vitellus compact et dense, plus ou moins homogene oi^i les 

 vesicules claires font defaut. . . . A ce moment, on 

 distingue dans I'oocyte de Y. noctula une zone centrale 

 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 Yesperuga 

 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 snrtout a un pole de I'ceuf, a celui oppose au pole oil se 

 detachent les deux globules polaires. Ce pole, oii 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 abondance au pole 



