G4 PROCEEDINGS OP THE AMERICAN ACADEMY 



meinem Material auf Grund von Schnittserien ersehen Icami, ziir Bil- 

 dunri jener Sc/iicht, die als Plasmodium, Coticke intermediaire, sekim- 

 diires Entoderm, etc. bekannt ist. Eine vom Beginn der Farchung an 

 als utitere Keimschicht avftretende kernhaltige Protoplasmamnsse, welche 

 z. B. hei den Salmoniden so deutlich als Plasmodium des Keimes, oder 

 sagen unr als primcires Entoderm aiiftritt, fehlt meinen Priiparaten 

 iiber Gohius." 



Rauber appears to regard this mode of origin not only as doubtful, 

 but as exceptional ; for he straightway assents to the view maintained 

 by Hoffmann, as true of teleostei in general, differing from him only 

 in holding that the plasmodium is a part of the germinal disc, which 

 from its destination, should be designated as " primary entoderm." 

 The origin of the periblastic nuclei from marginal cells does not sus- 

 tain Rauber's opinion in regard to the comparative rank of the plas- 

 modium (1. c. pp. 300, 320). 



Hoffmann maintains that tlie periblastic layer is separated from 

 the blastndisc as the result of the first cleavage, and that it remains 

 ever after distinct from it, taking no direct part in forming the embryo. 

 In regard to its function, he comes to the conclusion, " in dieser 

 Kernschicht die Werkstiitte zu sehen, welche die Bestandtheile des 

 Nahrungsdotters, des Parablast, assimiliret, um Zellen des Ai-chiblast 

 oder dem von ihm abstainmenden Embryo in eine fiir die Erniihrung 

 geeignetere Form zu iiberreichen, mit anderen Wortcn, die an Ker- 

 nen reiche Protoplasmaschicht des Parablast functionirt als pro- 

 visorisches Bhit."* This view of its function is however not wholly 

 original with Hoffmaim ; for a similar idea had previously found ex- 

 pression in the writings of several embryologists, among whom may 

 be mentioned Balfour and Klein, and more recently, but independently 

 of Hoffmann's observations, Ryder, Kingsley, and Conn. Hoffmann 

 states tliat the blastodisc grows during cleavage at the expense of 

 nutritive material brought to it by the periblast, thereby overlooking 

 the fact that it grows at the expense of the periblast itself. 



With reference to the origin of the periblastic nuclei, Ryder ^^ has 

 suggested that the periblast may retain some portion of " the original 

 nuclear matter of the egg," which may be the source of free nuclei in 

 the yolk. In a recent paper" he has stated more at length his views 

 on the function of the periblast, which he calls the "yolk hypoblast" 



* I. c, pp. 136, 137. 



86 Ryder. Bull. U. S. Fish Com., I, p. 298, 1881. 



6T Ibid., II., pp. 183-187, 1882. 



