428 Leland Griggs. 



Eycleshymer ('95) in his observations on Amblystoma not 

 only observed a distinction between neural and primitive grooves 

 but he records a division of the neural groove into two parts. 

 The anterior part of the neural groove usually appears first 

 before the neural crests are clearly formed, and then "sl second 

 groove is often observed lying between the posterior end of the 

 neural groove and the blastopore." This groove he calls the 

 ''dorsal groove." He notes that it is sometimes absent and 

 again sometimes the neural groove appears to run forward ''as 

 a continuation of the slit-like blastopore." He considers the 

 dorsal groove as really "a part of the neural groove having arisen 

 in precisely the same manner." His figures indicate in later 

 stages an anterior pit, but no mention is made of it. Eycleshy- 

 mer has thus gone farther than any other writer in analyzing 

 the single primitive groove of Miss Johnson into three grooves, 

 "the primitive groove," "the dorsal groove," and "the neural 

 groove." 



More recent writers have failed to notice these three grooves. 

 Morgan ('97) who adopts the old terminology applies the term 

 "primitive groove" to the whole series of grooves in the frog, 

 but he makes the significant statement that in older embryos 

 "the primitive groove is narrower." It will be shown in this 

 paper that this apparent narrowing of the old groove is in reality 

 the appearance of a new groove after the disappearance of the 

 old one. 



Semon ('01) insists that in Ceratodus there is undoubtedly 

 a lengthening of the groove which arises from the closing of the 

 blastopore. It must be admitted that this is what would be 

 expected since the groove lies in the growing region of the 

 embryo. The condition in Amblystoma seems to resemble 

 very closely the structure which he has figured for Ceratodus. 

 Earlier authors who claimed that the primitive groove was 

 shorter than the diameter of the original blastopore were cor- 

 rect so far as the first appearance of the groove was concerned, 

 but Semon has shown that they overlooked the fact of a later 

 growth which can be demonstrated in Ceratodus only by sec- 

 tions which show the typical fusion of the germ layers extend- 



