352 HOEACE W. STUNKARD 



''Whether we find the median plate smooth in Amblystoma or 

 faintly segmented depends on the stage at which the examina- 

 tion is made, and we recognize that the appearances in any one 

 egg are not constant throughout the open groove stage; further, 

 that eggs of closely related animals are by no means necessarily 

 similar at corresponding stages." According to Griggs, the 

 beaded appearance of the neural crests was not apparent in any 

 of the embryos of this stage examined by him, and he argues 

 for the metameric significance of the median divisions. Locy 

 and Griggs both attempt to establish neuromerism as a basis 

 for determining the segmentation of the head, but their results 

 are mutually exclusive and contradictory. 



Locy's statement that primary neuromeres are visible in the 

 blastoderm of the chick at the twelfth hour of incubation, just as 

 the head fold is first outlined, and that they extend into the 

 primitive streak, finds absolutelj^ no support in any of the- 

 material of the present investigation. His further statement 

 that ''the cells in these segments are characteristically arranged, 

 even in the earhest stages, and their arrangement and struc- 

 ture would indicate that they are definite differentiations of cell 

 areas" was denied by Hill, and in the present study evidence to 

 support this statement of Locy is also entirely wanting. Neal 

 ('98) called attention to the fact that "none of the reproductions 

 of Locy's photographs, with two possible exceptions, show a 

 segmentation of the neural folds in either the trunk or embryonic 

 rim." He might well have added that none show neuromeres of 

 both sides and that the same embryo was not photographed 

 twice, in two different positions (which probably would be 

 necessary) that the neuromeres of the two sides might be com- 

 pared. In fact, Locj^'s photographs, in my opinion, deny rather 

 than confirm his statement. He admits that his drawings "are 

 a little too distinct" and "the exactness has been exaggerated." 

 Hill's figures of the chick have called forth exclamations of 

 surprise and astonishment on all sides. He figures constrictions 

 of his primary neuromerism persisting in embryos with a closed 

 neural groove, but I have been unable to observe such a condi- 

 tion. It is a significant fact that the cell arrangement of the 



