158 



The same tale is told with reference to the fore brain and noto- 

 chord. It must of course be understood that the point marked x is 

 the only point actually marked by the sable on the segmented egg. 



Sable 



hb 



Fig. 2. Rana tempo- 

 raria. A Side view of egg 

 shewing exact position of 

 the sable. B and C Longi- 

 tudinal sections of the same 

 embryo after some days. 

 C cement organ, per peri- 

 cardium. Other letters as 

 before. 



Fig. 2 B shews at [ph) the part of the gut which has been formed 

 by the splitting among the cells and due entirely to the primary growth 

 centre, and therefore true archenteron. 



Figures 3 and 4 explain themselves, and shew roughly the parts 

 of the embryo laid down dorsally during the gradual closure of the 

 blastopore. 



Fig. 5 represents a case in which the bristle was inserted 0,5 mm 

 from the right side of the half formed blastopore. The bristle appeared 

 later to perforate the side of the body far in front of the anus and 

 tail bud. 



A sable placed a little to one side of the mid ventral line moves 

 upwards as the blastopore closes and is found eventually ou the side 

 more dorsal than the anus; which is due no doubt to the peculiar way 

 in which the hinder part of the blastopore closes in the Frog. 



Only a very small part is formed actually ventral (anterior) to 

 the anus. As the blastopore closes, the elongated primitive streak 

 forms and in the more ventral part of this the anus arises. The part 

 formed in the mid ventral line from the secondary growth centre is 



