374 EYCLESHYMER. [Vol. X. 



The center of the dark hemisphere was punctured in early 

 and late segmentation stages, and the location of the extra- 

 ovate observed when the embryo was formed. The results 

 were variable. In 7 eggs the extra-ovate occupied a position 

 near the median line, just beyond the region of the cephalic 

 portion of the neural fold. In 5 cases it was located just within 

 this fold ; in 4, on the right side of the median line ; and in i, 

 on the left. 



The cause of these slight variations is probably due to the 

 fact that punctures cannot be made at the same point in the 

 different eggs. 



From these experiments I conclude that the apical pole 

 corresponds to the later head region of the embryo. This 

 observation accords with what occurs in the Teleost ^%,'g, 

 as stated by Professor Whitman in lectures on vertebrate 

 embryology. 



Schultze ('87) believes, however, that in Rana the apical pole 

 represents the mid-dorsal region of the embryo. 



Roux ('88®), in the same form, holds that the apical pole 

 forms the ventral side of the embryo. 



Were it true that the apical pole later forms the ventral part 

 of the embryo, we should expect to find considerable pigment in 

 this region, as well as an area of smaller cells, which is not the case. 



If at the first appearance of invagination a puncture is made 

 in the dorsal lip of the blastopore, much variation occurs in 

 the later position of the extra-ovate, probably owing to the 

 difficulty in locating the median portion of the embryonic area. 

 It will be recalled that one side of the groove may extend 

 more rapidly than the other. If, however, the puncture is 

 made at a time when the blastopore is crescentic or horse-shoe 

 shaped, there is less difficulty in orienting the embryo. In 

 all cases (17 eggs) the extra-ovate lies in the posterior third of 

 the embryo. 



Concerning the fate of the dorsal lip of the blastopore, we 

 have but the observations of Schultze ('87) and Roux ('88®). The 

 former finds a defect in this region to later lie in the posterior 

 portion of the embryo, while Roux finds that an injury pro- 

 duced here later lies near the transverse fold of the head. 



