432 Leland Griggs. 



an exception to the usual number of neuromeres in ttie hind- 

 brain. 



Very extensive observations on the neuromeres of the closed 

 tube have been made by Locy ('95) and Hill ('00). Their work 

 has been of especial value owing to the fact that they have shown 

 the direct correspondence between the segments of the neural 

 tube and those of the neural crests before the tube is formed. 

 By following carefully the history of the segments in the anterior 

 end of the crests they observed in the anterior end of the neural 

 tube a few transitory segments which had not been seen before. 

 Locy found in the fore-brain of Acanthias three segments, in the 

 mid-brain two and in the hind-brain nine, counting three in 

 in the vagus region which are not included in the brain by earlier 

 writers. Hill in his work on the trout and chick confirmed 

 Locy's investigations. Johnston ('05) also claims to have con- 

 firmed these results in his work on Amblystoma which he has not 

 yet published. 



Thus we have presented to us by Locy, Hill and Johnston a 

 fairly complete account of the neuromeres of the brain. Accord- 

 ing to this account there are eleven similar divisions in the ante- 

 rior end of the neural plate which constitute a cephalic plate, 

 not, however, marked off from the rest of the plate except by 

 their subsequent history. The segments extend laterally across 

 the neural crests and after the tube is formed the divisions extend 

 completely around it. The segments in the hind-brain are 

 those already investigated by earlier authors. They persist 

 until the nerve relations can be fairly well determined. In the 

 fore-brain and mid- brain, however, the segments are transitory. 

 In the fore-brain they completely disappear before the differen- 

 tiation of the secondary fore-brain and thalamencephalon. 



Kupffer ('03, '05) has recently described a series of segments, 

 his so-called secondary neuromeres, which he has shown to be 

 quite generally present in vertebrate embryos. His fore-brain 

 divisions telencephalon, parencephalon, synencephalon, although 

 they agree in number with Locy's divisions, are evidently not 

 the same, for Locy has shown that his divisions disappear before 

 there is any trace of this later differentiation of Ihe fore-brain. 



