444 Leland Griggs. 



Stage 2 (Fig. 1, A; Plate I, fig. 1). The posterior germinal 

 depression now shows some changes (pgd fig. 1, A). It is nar- 

 rower, deeper and more clearly defined since the shallow pits 

 have disappeared. The anterior end has not changed in posi- 

 tion, but the posterior end has begun to widen out and disappear 

 leaving a considerable distance between the closing blastopore 

 and the posterior germinal depression. 



A new groove, the anterior germinal depression (agd) a struc- 

 ture very constant in its nature and present in all eggs of the 

 right stage, has now appeared in front of the posterior depres- 

 sion. In the photograph (Plate I, fig. 1) the depression is not 

 so sharply defined as in the figure. It becomes more and more 

 sharply defined in succeeding stages, however, as may be seen 

 by examining the photographs of older embryos. It is evidently 

 not one of the pits described in the preceding stage since it is 

 deeper, narrower, and longer, and furthermore the pits of the 

 posterior depression have all disappeared at this time. These 

 facts together with its very important later history give sufficient 

 ground for considering it a separate and distinct structure. 



This anterior germinal depression is evidently the groove 

 which Eycleshymer ('95) in describing the early development of 

 Rana and Amblystoma has called the neural groove proper, which 

 he found to be connected with the groove derived from the blasto- 

 pore by a third groove which he called the dorsal groove, evi- 

 dently identical with the posterior depression described above. 

 Morgan ('97) for Rana has figured the posterior part of what he 

 has named the primitive groove as forming first, and later the 

 anterior part appearing as a continuation of the part first formed. 

 Evidently he observed the same process as Eycleshymer has 

 described more fully. Neither of these authors, however, has 

 described in detail the character of these two grooves nor traced 

 their later history. 



The value of adopting the new terms anterior and posterior 

 germinal depression must now be apparent. It has just been 

 shown to be a mistake to call the posterior depression a primitive 

 groove, if by that term is meant a groove derived from the 

 blastopore. It is obviously just as much a mistake to call the 



