430 • Leland Griggs. 



region of the anlage of the ear. Two of the dividing grooves 

 appear deeper than the rest and so furnish convenient landmarks 

 which no previous investigator had been able to find. The 

 anterior of the two grooves proves to lie between the fore and 

 the mid-brain, while the posterior one lies just back of the cere- 

 bellum. Thus Hill is able to show that there are three of these 

 segments in the fore-brain, and two in the mid-brain. The 

 general features of this segmentation were confirmed by the 

 study of the chick of one somite although here the larger grooves 

 were absent. 



A comparison of the results obtained by these various authors 

 is difficult, especially as to the number of segments, since Hill 

 is the only one to find definite persisting landmarks. But the 

 numerous observations as to the presence of some kind of divi- 

 sion in the open neural plate is sufficient to warrant further 

 research. 



Turn ng now to the segmentation of the neural crests as they 

 first appear at the sides of the neural plate we find that in Ambly- 

 stoma embryos such a segmentation has been observed by 

 Eycleshymer ('95) and Locy ('95). The former considers the 

 appearance of segmentation merely an artificial scalloping due 

 to the reagents used, because he finds variation among various 

 embryos. The latter, however, regards the segments as true 

 neuromeres, but he did little work on Amblystoma and that 

 merely to confirm his work on Acanthias. 



In Acanthias Locy ('95) finds a series of segments in the neural 

 ridges which he is able to trace through the closing of the neural 

 tube and the formation of the brain vesicles. The fore-brain 

 contains three segments, the mid-brain two and the hind-brain 

 nine. Hill ('00) has confirmed these observations in his study 

 of the chick embryo. He finds that the grooves which separate 

 the segments extend entirely across the neural plate. This is 

 the only observation yet made showing that the segmentation 

 of neural crests agrees with that of the open neural plate. The 

 accuracy of this observation has been called in question by 

 Kupffer ('03). 



