342 Journal of Comparative Neurology. 



Dale ('go) in his investigation above referred to, reports 

 having made a set of similar counts for one of the coccygeal 

 nerves of the cat. His paper deals principally with the num- 

 ber and diameter of the fibers found in single sections of the 

 nerve roots and trunk. However, he states that, in order to 

 test the findings previously published from this laboratory as 

 to the variations in the number of fibers at different levels, he 

 counted "Sections of the roots and trunk taken near the gan- 

 glion and again sections at some distance from the ganglion on 

 either side." These counts were for one 4th. coccygeal nerve. 

 He reports having found no variation in the number of fibers 

 either in the ventral root or in the trunk. In the dorsal root 

 he found a few more fibers in the section taken at a distance 

 from the spinal cord than in the one taken near the ganglion — 

 a variation in the opposite direction from that here found in 

 the nerves of the frog. That Dale's result does not agree with 

 the results previously obtained and here extended is probably 

 due to the fact that the growth of the nervous system of the 

 frog is much slower than that of the mammal. The cat has a 

 fixed period of growth while the frog, if it does not grow as 

 long as it lives, at least cannot be said not to do so. It cannot 

 be said that any of the specimens here employed had attained 

 their full growth. Further, it is not known whether the fibers 

 in the spinal nerves of the mammals increase in number while 

 the animal is acquiring its extra-uterine growth. It would be 

 interesting to determine whether an adult cat has a greater 

 number of fibers in its coccygeal nerves, for example, than a 

 young kitten. Schiller ('89) counted the fibers in the oculo- 

 motor nerves of three cats at birth, and several at later ages. 

 His averages give the adult cat so few more fibers (3 % ) than 

 the new-born, as to indicate that this nerve at least, of the cat, 

 early acquires its numerical completeness. It has been amply 

 shown that the nerves of the older frogs contain considerably 

 more fibers than those of the young ones, and one of the pur- 

 poses of this paper is to determine the rate at which this greater 

 number is acquired. 



The roots of the various nerves of a given frog vary greatly 



