30 Journal of Comparative Neurology and Psychology. 



IV. The number of spinal ganglion cells and their relation to 

 the number of fic>~i'e fibers connected zvith the ganglion. 



It is seen in column A and B. Table I, that the numbers 

 of ganglion cells vary much as do the numbers of fibers in the 

 dorsal roots. This is to be expected. But it is also seen that 

 there are many more cell-bodies in the ganglia than there are 

 fibers in the corresponding dorsal roots. The counts show a gen- 

 eral average of three times as many cells in the ganglia as fibers 

 in the dorsal roots. The averages obtained for each of the three 

 nerves are quite similar, being somewhat greater for the Vth 

 and Vlth than for the IXth. The ratios (col. C) show no tend- 

 ency in either of the nerves to vary with the weight of the 

 animal. 



This excess of cells in the spinal ganglion above the num- 

 ber of fibers in the dorsal root agrees fairly well with the re- 

 sults obtained by Hodge ('88) whose paper, as far as I am 

 aware, is the only other dealing with an American species of 

 frog. He counted the ganglion cells and dorsal root fibers in 

 the VHth, Vnithand IXth nerves of a single specimen and ob- 

 tained ratios of cells to fibers of 1:2.5, 1:2.9, ^-S-S respectively, 

 giving an average of 2.9 cells per each dorsal root fiber. Buhlek 

 ('98) investigating the spinal ganglia of Rana esculenta, counted 

 the cells and dorsal root fibers of one of the IXth nerves" of one 

 specimen and found 5 cells per fiber. This is considerably 

 higher than any of my results. It may have been peculiar to 

 the one nerve investigated or it may be peculiar to the species. 

 For the mammals, Gaule and Lewin ('96) found in the 

 XXXIIth nerve of the rabbit 6.4 spinal ganglion cells per fiber 

 in the dorsal root of the nerve, and Hatai ('02) for three of the 

 spinal nerves of each of four white rats of different ages, ob- 

 tained excesses of cells ranging from 11.5 in the younger down 

 to 2.7 per fiber in the adult, always finding twice as many cells 

 as dorsal root fibers. On the other hand, Freud ('78) working 

 with the less perfect technique of his time, concluded that in 

 Petromyzon the number of spinal ganglion cells were equal to- 

 the number of dorsal root fibers. 



