120 J. P. HILL. 



Prozess audi in solcheu Eiblaseu der Saugetiere voi'koinmen 

 kann, die iiberliaupt nicht, oder erst spater mit dein Uterus 

 verwachsen, so kann die Keimfeld-Entypie zwar durch die 

 friilie Vervvaclisung veranlasst, aber nicht ausscliliesslich 

 liervorgerufen werden." He goes on to remark that — " Die 

 Vorbedingungen zur Entypie miissen in der Struktur der ver- 

 wachsenden Eibhise gesucht werden/^ and expresses his 

 agreement with the views of Van Beneden as to the signifi- 

 cance to be attributed to the early cleavoge phenomena in 

 Eutheria. 



The attitude of the iUustrious Belgian embryologist whose 

 loss we have so recently to deplore, towards this problem is 

 clearly set forth in the last memoir which issued from bis 

 hand. "Je suis de ceux/' he wrote ('99, p. 332), "qui penseut 

 que toute I'embryologiedes Matnmiferes placentaires temoigne 

 qu'iis derivent d'animaux qui, comme les Sauropsides et les 

 Monotremes, produisaient des oeufs meroblastiques. Je ne 

 puis a aucun point de vue me rallier aux idees contraires forniu- 

 lees et defendues par Hubrecht. L'hypothese de Hubrecht 

 se heurte a des difficultes morphologiques et physiologiques 

 insurmontables : elle laisse inexpliquee I'existence, chez les 

 Mammiferes placentaires, d'une vesicule ombilicale et d'une 

 foule de caracteres commnns a tous les Amniotes et distinctifs 

 de ces aniinaux." Holding this view of the origin of the 

 Eutheria, Van Beneden based his interpretation of their early 

 ontogenetic phenomena on the belief that '' la reduction pro- 

 gressive du volume de l'a3uf d'une part, le fait de sou 

 developpement intniuterin de I'autre out du avoir une in- 

 fluence preponderante sur les premiers processus evolutifs." 



Balfour, in his classical treatise, had already some eighteen 

 years earlier expressed precisely the same view. "The 

 features of the development of the placental Mammalia," he 

 wrote (•'Mem. Edn,,' vol. iii, p. 289), "receive their most 

 satisfactory explanation on tluj hypothesis that their ancestors 

 were provided with a large-yolked ovum like that of Saurop- 

 sida. The food-yolk must be supposed to have ceased to be 

 developed on the establishment of a maternal nutrition through 



