64 Journal of Comparative Neurology. 



The fasciculus communis system in Petromyzon presents 

 in general the same relations as in Acipenser. It is much 

 smaller than in Acipenser, cells of the II type have not been 

 found, and the secondary tract is too small and diffuse to be 

 traced. The small size of the system and the absence (or 

 paucity) of II type cells must be regarded as primitive char- 

 acters. The latter leads the writer to doubt whether the II type 

 cells in the lobus vagi of Acipenser have the importance which 

 has been attributed to them. In Petromyzon the cells are more 

 primitive in their form and position than in Acipenser, and the 

 communis center is not nearly so highly developed as the cuta- 

 neous centers. Compare Figs. 8 and ii. 



The central connections between the cutaneous and visceral 

 systems are, as the writer has shown ('oi c, p. 119, 126), nil. 

 The study of the brain of Petromyzon supports in every partic- 

 ular the conclusions on this point drawn from the brain of Aci- 

 penser, and furnishes additional evidence owing to the greater 

 development of the spinal portion of the communis system. 

 Petromyzon is to be added to the list of lower vertebrates in 

 which the median nucleus and cervical bundle of Cajal have 

 been described (cf. Johnston '01 c, p. 126). It is to be noted 

 that the cervical bundle is much larger and extends farther cau- 

 dally than in any other vertebrate, while the median nucleus 

 merges with the central grey matter immediately dorsal to the 

 canal. It seems probable that the visceral center in the cord is 

 larger in Petromyzon than in higher forms, and it is pretty well 

 established for all vertebrates that this center is wholly distinct 

 from the cutaneous center in the cord, lying mesial to the latter 

 and bordering on the canal. This supports the view already 

 stated independently by C. J. Herrick ('99, p. 56-58) and the 

 writer ('01 c. p. 127). 



The fasciculus communis system includes fibers distributed 

 to general visceral surfaces and fibers to end-buds both in the 

 mouth and branchial cavities and on the outer surface of the 

 body. The writer has suggested ('01 c, p. 127—129) that these 

 buds have essentially the same function wherever situated, 

 namely to test the chemical quality of the water with respect 



