528 LOCV. [Vol. XI. 



front are seen three of the brain vesicles, — those of the fore- 

 brain, the mid-brain, and the cerebellum. The thalamencepha- 

 lon and the prosencephalon do not show as separate parts. In 

 the region of the hind-brain are seen three neuromeres espe- 

 cially well developed. They present the appearance of three 

 bars ; they are the seventh, eighth, and ninth neuromeres 

 respectively. The other neuromeres are present, but they do 

 not stand out with such distinctness as the three mentioned. 

 When the ear vesicle first arises it makes its appearance oppo- 

 site the ninth neuromere. 



Figs. 73, 74, and 75 are sections of a somewhat older em- 

 bryo after the ear vesicle is established. In these figures eight 

 neuromeres of the hind-brain are visible. The ear vesicle is 

 opposite the tenth neuromere. Just in front of it, in Figs. 73 

 and 74, are the roots of the eighth and seventh nerves, respec- 

 tively, those from the former nerve being connected with the 

 tenth neuromere, and those of the latter with the ninth neuro- 

 mere. 



In Fig. 75, the fifth nerve is seen to have connections with 

 the first and second neuromeres of the hind-brain, i.e., the sixth 

 and seventh neuromeres respectively. 



As already indicated, the eighth neuromere bears no nerve, 

 and Hoffmann remarks, " This seems to be the case in all 

 Vertebrates." 



IV. Supplementary Observations on Other Animals. 



I have also made some supplementary observations on these 

 neural segments in Amblystoma, Diemyctylus, Rana palus- 

 tris, Torpedo ocellata, and the chick. In all of these forms 

 the metameric divisions are to be found in very early stages 

 before any of the embryonic organs have been formed; and 

 they are in all essential features like those I have described for 

 Squalus acanthias. 



Figs. 113 and 114 (PI. XXX) show camera sketches of an 

 Amblystoma egg, with broadly expanded neural plate and widely 

 open neural groove. The neural folds or ridges are divided 

 throughout their length into a series of segments with no espe- 



