452 Leland Griggs. 



A large part of the eggs as Eycleshymer has observed show no 

 sign of this canal. His inference, however, that the canal is 

 never formed in those eggs in which it is not seen does not follow 

 necessarily, for like the transitory structures already described it 

 may appear and disappear very quickly. Eycleshymer's state- 

 ment could be proved only by following through the individual 

 development of a single egg. In the absense of such evidence 

 it is logical to conclude that the neurenteric canal, like the pos- 

 terior germinal depression and the neuromeres, is of very general 

 occurrence. The growth in length of the embryo which becomes 

 apparent in this stage involves the question of whether or not 

 the blastogroove grows in length. This has been a matter of 

 dispute. Semon ('01) for Ceratodus has given perhaps the most 

 detailed and careful description of a growth in length of the 

 blastogroove. The earlier writers, Miss Johnson ('84) and 

 Schultze ('88), have confused the blastogroove with other grooves 

 and therefore their description of an elongating groove hardly 

 affords any light on this problem. Jordan ('93) distinctly states 

 that the blastogroove of the newt does not exceed in length the 

 diameter of the blastopore. Morgan ('97) and Eycleshymer 

 ('95) have not described any elongation in the various forms of 

 Amphibia which they have studied. An elongation of the blasto- 

 groove in Amblystoma is evident after the disappearance of the 

 neurenteric canal (bg, fig. 2, B) . This is a result of the general 

 elongation of the region in which the groove lies. The neural 

 plate, too, elongates rapidly in this region as can be seen by com- 

 paring drawings A and B in fig. 2, noting in each case the length 

 of the procephalic lobes as compared with the entire length of 

 the plate. Such an elongation carries back the posterior end of 

 the blastogroove and the anus. There is, however, no growing 

 forward of the blastogroove since its anterior end does not 

 approach the transverse cephalic groove but rather each end is 

 slowly receding from the transverse groove. Now that che 

 history of all four of these grooves has been traced, a more 

 detailed comparison may be made by means of transverse 

 sections. Fig. 3, A shows the anterior germinal depression 

 in its average condition as regards depth of groove, while fig. 



