574 WILLIAM PATTEN. 



What he described as the " Hautblatt " was probably the 

 amnion and serosa combined, and the " Muskelblatt '' the 

 ventral plate. The same author has figured an infolding similar 

 to that described as the ''gastrula/' but which, in his opinion, 

 is simply the secondary result of the formation of two lateral 

 thickenings or germinal ridges out of which the segments and 

 appendages of the body are formed. He states that the ridges 

 result from a lateral contraction, which causes a furrow to 

 appear on the inner surface of the ventral plate, and not by an 

 infolding of the outer surface, as shown in fig. 9, PI. XXXVIb. 

 It is difficult to decide which of these two infoldings Zaddach 

 had under observation when he wrote his description, but 

 judging from the fact that he ascribed the origin of the nervous 

 system to the germinal ridges on each side of the furrow, I 

 think it probable that what he saw was simply the neural 

 furrow. 



The endoderm arises from any point in the blasto- 

 derm by DELAMiNATioN, and this process may continue 

 even after the blastoderm has been converted into 

 the ventral plate. 



It will be remembered that no cells were left in the yolk after 

 the formation of the blastoderm. By examining sections of eggs 

 during the formation of the embryonic membranes, amoeboid 

 cells, containing large granular nuclei, can be seen in the yolk 

 both in the region of the ventral plate and in that of the serosa ; 

 in the latter one may occasionally find cells projecting into the 

 yolk and sending out ray-like arms of protoplasm; very often 

 two cells may be seen close together, one in the serosa, the other 

 just inside the yolk and connected with each other by proto- 

 plasmic filaments. Other more or less similar cells can be seen 

 in the immediate vicinity of the ventral plate, especially along 

 the median longitudinal line. Admitting the accuracy of the 

 observation in regard to the entire disappearance of the nuclei 

 from the yolk in the blastoderm stage, there are thus only two 

 possible interpretations for the present condition ; either these 

 yolk cells rise autogenously in the yolk and are migrating 

 towards the periphery, or certain cells of the serosa and ventral 



