The Nervous System of Ambly stoma. 429 



ing over a distance considerably greater than the diameter of 

 the blastopore. 



The natm'e of these grooves is not only in itself an interest- 

 ing problem which is not yet wholly solved, but the relation of 

 the grooves to the nervous system is also very important. It 

 has quite generally been taken for granted that these grooves, 

 one or all of them, are ''neural" grooves, but this relation has 

 never been well established. 



In turning now to the more important problem of the early 

 segmentation of the neural plate we find considerable divergence 

 of views. Kupffer ('93) describes the cephalic plate of Salaman- 

 dra atra as being divided into eight segments or primary neuro- 

 meres. The cephalic plate or "Hirnplatte" has no definite 

 boundary posteriorly but appears to coincide in extent with the 

 later '' Archencephalon," which the author finds to be a rather 

 vaguely defined vesicle comprising the region of the fore-brain, 

 mid-brain and a part of the hind-brain. Froriep ('91 and 

 '93) has made similar observations, although less complete 

 on Salamandra maculosa and Triton. In the cephalic plate 

 of the former he saw three or four segments, and in that of the 

 latter he saw five, but in both cases there is an unsegmented 

 tip which he thinks is large enough to represent three or four 

 segments. Froriep, however, thinks this appearance of segmen- 

 tation is merely due to the structure of the underlying meso- 

 derm. 



Later authors have made observations similar to those of 

 Kupffer and Froriep, and, like them, have failed to agree on an 

 interpretation. Eycleshymer ('95) finds in the neural plate of 

 Necturus and of Amblystoma several large segments which, 

 he considers, are caused by the mesoderm. Locy ('95) describes 

 a few faint lines of division in the open neural plate of Ambly- 

 stoma and four or five prominent divisions in the anterior end 

 of the plate of Rana palustris, but since these divisions do not 

 agree in number with the divisions of the neural plate which he 

 considers to be true neuromeres he denies their metameric value. 

 Hill ('00) has found in the solid anlage of the trout brain ten 

 segments extending from the anterior tip of the plate to the 



