Developmental history of primary segments of the vertebrate liead. 427 



pi'imitive vertebrœ appear as so many segments or metameres aud 

 one sees plainly from 8 to 9 segments in the region of the fourth 

 ventricle of the neural tube." (Author's translation.) 



KuPFFER, '86, in a brief paper (p. 469—476) reports finding five 

 segments in the hind-brain and three in the mid-brain of the trout. 

 As to the mid-brain and segmental criteria, he says : "Sagittal sections 

 through each embryo show three pair of segments in the vicinity of 

 the mid-brain that resemble those of the medulla oblongata, that is, 

 they are little swellings upon the floor and the sides of the medulla, 

 separated from one another by transverse grooves." (Author's trans- 

 lation.) 



Reighard, '90, figures and describes 6 segments in the hind- 

 brain of Stisostedion vitreum that in every way are identical with the 

 segments of this region in the trout. 



In my paper on The Development of the Epiphysis in Coregonus 

 albus (Hill, '91), I figure and briefly describe 11 segments in the 

 encephalon of the white fish eml)ryo 7 mm long, 60 days old. Five 

 of these are located in the primary fore- and mid-brains. 



The only paper dealing especially with this subject is that of 

 Waters, '92, who finds 11 segments in the encephalon of the cod. 

 He assigns a segmental value to the olfactory nerves and says: "The 

 region of the brain-wall giving rise to them shows markedly the 

 characteristics of a true neuromere as defined by Orr and is, I think, 

 the first or olfactory neuromere" (in : Quart. Journ. micr. Soc, V. 3, 

 p. 463). Regarding the encephalon just back of this olfactory neuro- 

 mere he writes: "While none of my cod sections give any reliable 

 evidence of a neuromere at this point 1 will show that in Amhlystoma 

 there is certainly a second neuromere aud that the optic diverticula 

 hold a curiously significant and close relation to it" (p. 464). His 

 direct evidence of a third neuromere in the primary fore- brain of the 

 cod is equally incomplete as the following quotation shows : "The 

 distance from the posterior commissure to the tern^ination of the 

 second neuromere is about one-third the entire length from before 

 backward to this point." . . . "From the fact that there is just sufficient 

 room at this point for another neuromere and that in Amhlystoma I 

 have been able more satisfactorily to prove its existence, I have called, 

 this the third neuromere, thus making the fore-brain contain three 

 neuromeres" (p. 464). 



In the region of the mid-brain Waters finds "two well marked 

 convolutions of the brain wall. These constrictions are shghtly smaller 



