344 



Roux, in 1888, performed a series of experiments which seemed 

 to show that the embryo forms in the white hemisphere as evidenced 

 by these words: "Der mit Hülfe der PpLüGER'schen Zwangslage von 

 mir angestellte Versuch, Froscheier, welche mit ihrer schwarzen Hemi- 

 sphäre nach unten auf eine Glasschale aufgesetzt waren, durch un- 

 genügende Quellung der Gallerthülle in Zwangslage zu erhalten und 

 und so jede Drehung des Eies innerhalb dieser Hülle zu verhindern, 

 hatte in Uebereinstimmung mit einer anders gewonnenen Beobachtung 

 Pflüger's ergeben, daß die Medullarwülste nicht, wie bisher angenommen 

 worden war, auf der oberen, schon von vornherein schwarzen Hälfte 

 des Eies zur Anlage kommen, sondern daß die Medullarwülste in ganzer 

 Länge auf der unteren, ursprünglich weißen, erst während der Gastru- 

 lation schwarz gewordenen Eihälfte gebildet werden." 



The controversy between Schultze and Roux concerning the position 

 of the embryo is familiar to all and need not be here rehearsed. The 

 quotations above given represent, so far as I am aware, both the 

 earlier and later views of the respective authors. 



The studies by 0. Hertwig on spina bifida in the embryo of 

 Triton led him to adopt the view of Roux, as expressed in the follow- 

 ing words: "In der Polemik, welche zwischen Roux und Oscar Schultze 

 über die Lage von Urmund und Nervenrohr in Bezug auf die Ober- 

 fläche der Blastula entstanden ist, muß ich mich auf die Seite von 

 Roux stellen." 



Morgan's conception of the formation of the Frog embryo is well 

 defined in the following quotation : "Pflüger, Roux and Hertwig have 

 come to the conclusion that the embryo forms over that part of the un- 

 segmented egg which is normally directed downwards, i. e. over the 

 white hemisphere. Schultze supports the old view, that the embryo 

 lies on the upper or black hemisphere. I was prepared therefore to 

 find some truth in each view, and expected to find the embryo forming 

 partly over the black, partly over the white hemisphere. I was then 

 not a little surprised to find that our studies led to the conclusion 

 that the embryo is formed over part of the white hemisphere of the 

 egg. In the main point, therefore, I am in agreement with Pflüger 

 and Roux, although not entirely so, for I hope to be able to show the 

 extent of the white hemisphere of the unsegmented egg, covered by 

 the blastopore, to be somewhat different from that affirmed by Pflüger 

 and Roux." 



Assheton's observations and experiments led to the belief that 

 the darker hemisphere contributes considerable material in the form- 

 ation of the head end of the embryo, viz: "Pflüger, however, thinks 



