26 Journal of Comparative Neurology and Psychology. 



In this table the results for each of the three spinal nerves 

 involved are grouped in the order of the body weights of the 

 respective animals employed in order that the figures obtained 

 for the different representatives of a given spinal nerve may be 

 compared more readily with each other as well as with those 

 of the other spinal nerves. 



In the first place, it is apparent as far as the three nerves 

 presented are concerned that neither the number of fibers nor the 

 number of ganglion cells in a given nerve of a specimen is regularly 

 dependent upon the body weight of the specimen. This is per- 

 haps entirely due to a fact noted previously ('99) when was 

 given a more detailed description of the macroscopic features of 

 the different spinal nerves of the frog, viz. : that when the 

 spinal neves of the different specimens are are compared, the 

 relative proportion of fibers distributed to a given nerve is by 

 no means fixed. The variations in proportional size are more 

 frequent and marked in the Vllth, Vlllth, and IXth nerves. 

 In the general arrangement, the Vlth is much smaller than the 

 Vllth, and the Vlllth (the largest of the lumbar nerves) is con- 

 siderably larger than the IXth; but occasionally the relative 

 size of these nerves can be observed even with the unaided eye 

 as decidedly different in different frogs and sometimes, indeed, 

 on the two sides of the same frog. The variations are most 

 frequent in the Vlllth and IXth nerves, the apparent condition 

 being that a portion of the bulk usually possessed by the 

 Vlllth may be contributed to the IXth instead, for when the 

 proportional size of the IXth is greater than usual, that of the 

 Vlllth is less. In the case of the frog weighing 7.0 grams, 

 recorded in the table, it was noticed at the time of its dissec- 

 tion that the IXth nerves of both sides were appreciably larger 

 than the Vlllth nerves. It was included, however, because at 

 the time I was unable to obtain another specimen of Rana vi- 

 rescens as small as this. Some of the other discrepancies in the 

 increase in the number of fibers accompanying the increase in 

 body weight are without doubt due to similar variations. To 

 determine the real rate of the increase, all the spinal nerves of 

 the different specimens should of course be included in the 



