26o Journal of Comparative Neurology and Psychology. 



N. VI includes the ventral nerve of somite 4 (and that of 

 somite 5 ?) does not affect the the present question. It is an 

 important question, however, whether Hatschek's Occ. i, 2 

 and 7 are all general cutaneous nerves. If they are lateral line 

 nerves without general cutaneous fibers they are worthless for 

 the present purpose. The writer has described a branch from 

 the N. lateralis to this part of the skin. The cranial nerves of 

 Petromyzon require to be reinvestigated, but so far as our pres- 

 ent knowledge goes the above account of the relation of the 

 dorsal roots to the myotomes appears to the writer to be per- 

 fectly sound. 



The same relation of the nerves to the somites is found in 

 Spinax (12) where N. IX Hes behind somite 4, N. X behind 

 somite 5, and a rudimentary ganglion is formed behind each of 

 the following somites. Six of these rudimentary dorsal nerves 

 eventually disappear owing to the reduction and shifting of 

 myotomes and consequent reduction of cutaneous area. 



Hatschek in 1892 came to the same conclusion as I have 

 stated with regard to the relation of dorsal roots to myotomes in 

 Amphioxus and cyclostomes. In 1893 he published a brief 

 correction (45) in which he said that in all higher vertebrates 

 the dorsal root unites with the next following ventral root. 

 This can be made out most readily, he says, in amphibian larvae. 

 I have examined such sections of amphibian embryos as I have 

 by me and although I have none old enough to show the distri- 

 bution of the nerve rami, I find two facts opposed to Hatschek's 

 statement. The dorsal roots are always a short distance caudal 

 to the ventral roots, and the ventral roots run across the 

 cephalic face of the ganglia. I do not see how this could result 

 if each dorsal root joined the next following ventral root. I 

 hope soon to investigate the matter farther in Amblystoma. 



The second statement of Hatschek seems to have been 

 generally accepted by later workers. I am inclined to think 

 that his first statement was correct for the fishes at least. 

 20. Comparison of head and Mink. 



Aside from the development of special organs in the head, 

 the chief differences between the head and trunk lie in the skele- 



