446 Iceland Griggs. 



latter's length is not greater than the diameter of the circular 

 blastopore. 



Stage 4 (Fig. 1, D, E, F. Plate I, figs. 3, 4, 5) . From this time on 

 the three grooves, the development of which has just been traced, 

 undergo rapid modification. The posterior germinal groove shows 

 unmistakable signs of degeneration in all eggs of this stage. In 

 fig. 1, D, and in Plate I, fig. 3 there is no sign whatever of the 

 original groove, a condition which is found in about one-third 

 of the eggs. In a few eggs, although the groove has disappeared, 

 there is a faint dark line marking its former position. 



The only remaining portion of the anterior germinal depression 

 (agd) in fig. 1, D, is a short deep groove or rather pit, and this 

 deeper portion of the original groove may be seen in some eggs 

 before the disappearance of the main part of the groove (agd, 

 fig. 1, E). Miss Johnson ('84) seems to have been the first one 

 to describe this "anterior pit" as she calls it but she failed to 

 notice the series of germinal grooves, apparently considering 

 the anterior pit as a part of one long primitive groove. Eycle- 

 shymer's ('85) figures of Necturus show a similar structure and 

 he seems to have considered the pit a part of the "neural groove." 

 His figures as well as those of Miss Johnson are representations 

 of older embryos than those of this stage of Amblystoma now 

 under consideration, and the single long groove evidently corre- 

 sponds to the neural groove proper which will be described 

 shortly. Hence their figures showing the relation of the pit to 

 a single long groove are correct. The history of this pit, how- 

 ever, as will appear from an examination of the various stages 

 shown in fig. 1, indicates that it is in reality the deeper and per- 

 sisting part of the anterior germinal depression. A study of 

 succeeding stages corroborates this view. 



The neural plate in this stage is marked off by a peripheral 

 groove (pg). This new groove does not take its origin from a 

 given point from which it grows forward or backward but from 

 the first it extends for a considerable distance along the sides 

 of the plate and, although very faintly, across the anterior end 

 of the plate. It cannot at its first appearance be traced around 

 the posterior end of the plate. As the photograph and the 



