No. 3-] THE VERTEBRATE HEAD. 507 



eight pairs of neural segments in the median part of the hind- 

 brain. It is to be carefully noted that these segments observed 

 by Kupffer were in embryos with a wide open neural groove, 

 and occupied the median part of the cephalic plate, thus giving 

 a "mediane Gliederung des Hirnes." In 1893, in his 

 " Vergleichende Entwicklungsgeschichte des Kopfes der 

 Kranioten," he gives figures {20 a and 20 b) of the forms 

 described in 1885. These figures of Salamandra atra show 

 segmental folds only in the median part of the neural plate, 

 and none in the neural ridges. This is interesting when com- 

 pared with my observations on amphibian eggs (see p. 529). 



In addition to the eight segments in the brain region he 

 counted thirteen or fourteen in the cord, extending backwards 

 to a point a little in front of the blastopore. 



Rabl ('85) speaks of unmistakable segmentation in the hind- 

 brain of chick embryos of from fifty to ninety hours' incubation. 

 He found seven or eight segments in the region of the fourth 

 ventricle — not being able to determine definitely whether 

 there were seven or eight. Again, in 1892, Rabl has most 

 ably discussed the question of the metamerism of the head, but 

 as his paper deals almost exclusively with segmentation in the 

 mesoblast, it does not come in for attention in the present 

 connection. 



Oscar Hertwig gives the matter passing attention in the 

 third ('88) edition of " Lehrbuch der Entwicklungsgeschichte." 

 He is not inclined to attach much importance to the neural 

 segments. 



Gegenbaur, also, does not look upon these particular seg- 

 ments as important factors in the metamerism of the head. 

 His position on the question is shown by the following quota- 

 tion so frequently met with : " So interessant und so vielver- 

 sprechend diese Thatsachen sind, so wenig scheinen sie mir 

 gegenwartig geeignet, zur Beurtheilung der Metamerie des 

 Kopfes selbst als Factoren in Geltung gebracht zu werden." 



Orr, in 1887, traced very definitely the connection between 

 these segments in the hind-brain and cranial nerves. In 

 describing the segments he made use of the term " neuromeres," 

 which has been generally adopted on this side of the Atlantic. 



