428 CHARLES HILL, 



than those of the fore-brain and rather more semicircular in shape" 

 (p. 465). He also finds that the "radial arrangement of cells is 

 present". There can be but little doubt that the two segments de- 

 scribed by Waters in the mid-brain of the cod are identical with the 

 two mid-brain segments of the trout as described in this contribution. 

 From a study of the figures by Waters, I am inclined to believe the 

 author considered the internal transverse encephalic grooves as intra- 

 segmental in position when according to my interpretation they are 

 intersegmental and occupy the same morphological position as the 

 transverse internal crests of the chick encephalon (see page 423). So 

 far as number of encephalic segments are concerned and their distri- 

 bution, my observations on the trout agree with Waters. 



While my description agrees with Waters as to number of seg- 

 ments, they serve to point out certain discrepancies. His identification 

 of neuromeres in the fore-brain is vague and his enumeration is based 

 on analogy and largely on inference. The descriptions of neural seg- 

 ments in Teleosts in front of the medulla, as given in this paper are, 

 I believe, the only ones based entirely on direct observation of the 

 segmental structures themselves. 



The condition of the neural axis in front of the cerebellum is 

 especially well shown in the earliest stages and the existence of 5 

 segments in fore- and mid-brains is made evident. This is the first 

 satisfactory evidence of this condition that we have in the Teleosts, 

 LocY has shown the same in Elasmobranchs (Acanthias) and the chick. 

 At least, this region very early shows joints like those in the medulla. 

 They are formed in the same way, resemble them in all essential 

 particulars. It seems to me to be straining the point to deny that 

 these are segments when segmental value is assigned to the homo- 

 logous segments in the medullary region. 



Incidentally these observations show something about the probable 

 morphological front of the brain. Herrick, '91, writes: "The morpho- 

 logical front of the brain cannot be beyond the infundibulum" (in : 

 Journ. comp. Neurol., p. 168). His, '93, believes the cephalad extremity 

 of the neural tube in chick embryos is turned ventro-caudad and the 

 morphological front of the neural axis therefore is in the vicinity of 

 the recessus infundibuli, while Kupffer sums up the evidence as 

 follows: "Is the neural tul)e open anteriorly then the neural axis 

 terminates in this opening; is the end of the tube bent, then the 

 neural axis follows this curve. I consider therefore, that the en- 



