THE EAELY DEVELOPMENT OF THE MAESUPIALIA. 15 



vations of Yan der Striclit ['03, '05] on the structure and 

 polarity of the ovum of the bat (Vesperugo noctula), since 

 these observations are in essential agreement with my own 

 on the ovum of Dasyurus, and enable me to affirm that the 

 pohir differentiation herein recorded for the first time for the 

 Marsupial ovum is attained as the result of vitellogenetic 

 processes, which essentially correspond with those of the ovum 

 of the bat. Van der Stricht, as is well known, has made a 

 special study of the process of vitellogenesis in the Eutherian 

 ovum, and is, indeed, at the present time the foremost 

 authority on this particular subject, so that his views are 

 worthy of all respect. 



Study of the oocyte of Vesperugo during the period of 

 growth shows, according to Van der Striclit, that " a un 

 moment donne du developpement du jeune oeuf, les boyaux 

 et amas vitellogenes [derived, according to him, from ' une 

 couche vitellogene, mitochoudriale,' present in the young 

 oocyte in the first stage of growth] disparaissent au profit du 

 vitellus, dont la structure pseudo - alveolaire s'accentue 

 graduellement." The full-grown oocyte at the stage just 

 prior to the appearance of the first polar spindle is charac- 

 terised by the presence of this " pseudo-alveolar structure " 

 throughout the extent of its cytoplasmic body. The alveoli 

 or vacuoles are of variable size, are filled by a clear liquid, 

 and " correspondent incontestablement au deutoplasma de 

 Foeuf. A ce stade du developpement de Toocj^te, ce vitellus 

 nutritif, auquel s'ajoutent bientot des granulations graisseuses, 

 est repandu uniformement dans toutes les profondeurs du 

 cytoplasme. Nulle part on ne constate une zone deutoplas- 

 mique distiucte d'une zone de vitellus plastique." In 

 Dasyurus the stage in vitellogenesis which almost exactly 

 corresponds with that of the full-grown oocyte of Vesperugo 

 just described is seen in oocytes not quite full-groAvn. In 

 fig. 4 is shown an oocyte of Dasyurus (-26 x '20 mm. in 

 diameter), in which the same pseudo-alveolar structure as 

 described by Van der Stricht for the Vesperugo oocyte is 

 perfectly distinct. Here, however, fatty particles are not 



