450 Leland Griggs. 



germinal depression is in various stages of degeneration, while in 

 Plate I, fig. 1 1 the sharply defined neural groove is seen, being 

 especially prominent in the posterior half of the neural plate. 

 Photographs of succeeding stages, all except Plate I, figs. 8, 9^ 

 show the neural groove. The anterior germinal depression 

 persists as a long narrow pit near the anterior end of the neural 

 groove but not extending exactly to the end of the groove (agd^ 

 fig. 2, F). The neural groove is seen in but a small proportion 

 of the eggs of this stage but after stage 7 is present in all the eggs 

 and persists to the closing of the neural canal. It may properly 

 be called a neural groove. While the two grooves called the 

 germinal depressions appear before there is the slightest indica- 

 tion of a nervous system and begin to degenerate before the 

 anlage of the nervous system is clearly defined, this third groove 

 appears as the neural plate is forming and persists even in the 

 fully formed neural canal. It is the only groove the history 

 of which is closely identified with that of the nervous system. 



The germinal depressions present in this stage show no new 

 features. The anterior depression in the majority of eggs is 

 short and deep and clearly marked (agd, fig. 2, A, C; Plate I, 

 figs. 4, 5, 6), but in a few eggs it is impossible to make the dis- 

 tinction between the anterior depression and the posterior 

 depression or neural groove. The posterior depression, as in 

 stage 4, is either absent (fig. 2, A) or is very wide and shallow 

 (fig. 2, B, C, E). 



The transverse cephalic groove has now extended in a few 

 eggs until it entirely cuts off the procephalic lobes (teg, fig. 2, A, 

 Plate I, figs. 6, 7). This groove shows considerable variation 

 in length and width as the figures show. Moreover, it may 

 extend clear across one-half of the neural plate before it shows 

 at all on the other half (teg, fig. 2, C; Plate I, fig. 6). In the 

 latter case the embryo usually shows other signs of more rapid 

 development on that side where the groove is present. The 

 infundibular depression (id, fig. 2, C), for example, may show 

 on one side only or in later stages the neuromeres may develop 

 faster on one side than the other. 



