Hardesty, spinal Nerves of the Frog. 34j( 



The specimens entered in the table are divided into three 

 groups : a group of small specimens, a group of medium sized 

 specimens, and a group of larger specimens. Under each group 

 are given in their respective columns, the averages for that 

 group. 



It is seen by comparing the averages for the three groups 

 that in the nerves of the smaller and more rapidly growing 

 specimens, fibers are being added more rapidly than in the 

 larger specimens of the other two groups. Also, while the 

 differences are not so great, the figures show that fibers are 

 growing into the nerves of the medium sized specimens more 

 rapidly than in the larger specimens. 



Again, by comparing the averages it is seen that, for the 

 younger specimens, the percentage rate of increase in the num- 

 ber of fibers per millimeter of length is greater for the dorsal 

 root than for the ventral root and greater for the trunk than for 

 either root. It was shown by the figures obtained by Birge 

 ('82) that when all the spinal nerves are taken into account, the 

 sensory or dorsal root fibers of the growing animal increase 

 more rapidly than do those of the ventral root. For the 6th. 

 nerve, alone considered in Table III, this statement does not 

 hold in case of the medium sized specimens, but is again true 

 for the larger group. This discrepancy is almost wholly due 

 to a single exceptional case in the medium group. The value 

 of the variation found for the ventral root of the 25.1 gram 

 specimen is exceptionally high. The discrepancy would per- 

 haps disappear could all the spinal nerves be included. The 

 distribution of fibers to a given nerve is by no means fixed and 

 this may account for some irregularities in the 6th. nerve. 



As to the rate of increase in the trunk, it is seen that the 

 amount by which the trunk exceeds the rate of either root is 

 less for the medium specimens than for the small ones, while 

 for the large specimens the rate for the trunk is even exceeded 

 by that for the dorsal root. This might be considered as due 

 to the ingrowth or medullation of sympathetic fibers taking 

 place with relatively greater rapidity in the trunk of the older 

 fr og, but this is not at all probable. It can be shown that med- 



