Hardesty, spinal Nci'ves of the Frog. 347 



He investigated the matter only as far as the gain in the num- 

 ber of fibers contained in the ventral roots is concerned. He 

 counted the ventral root fibers of all the spinal nerves of one 

 side of six specimens ranging in weight from i}4 to 1 1 1 grams. 

 Then assuming that the numbers are approximately equal, he 

 doubled the numbers obtained for one side in order to get the 

 entire number of ventral root fibers present in the spinal nerves 

 of both sides. By dividing differences in number of fibers by 

 differences in weight in grams, he obtained in the six specimens, 

 an average of 5 i ventral root fibers gained for each gram gained 

 in weight. 



He also counted the fibers in the dorsal roots and in the 

 trunks of two of the frogs. His tables show that these frogs 

 weighed 23 and 63 grams respectively. Since Birge did not 

 include the dorsal branches, the figures thus obtainable would 

 not give the required relations for the trunk as here shown in 

 Table HI. If, however, the sums of the dorsal root fibers be 

 doubled in each case and the number thus obtained for the 23 

 gram frog be subtracted from that obtained for the 63 gram 

 frog and the difference in favor of the larger specimen be di- 

 vided by the difference in weight, there is found a gain of jy 

 dorsal root fibers for each additional gram in weight. 



In this paper unfortunately the 6th. spinal nerve only has 

 been examined and not the entire number of spinal nerves. An 

 attempt was made to estimate the total numbers of root fibers 

 for all the spinal nerves by taking the proportional values of 

 the 6th. nerve, obtainable from Birge's figures, and applying 

 those values to the figures here found. This attempt revealed 

 the fact that the species of frog used by Birge is not at all 

 comparable in this respect with that here employed. The 

 American Rana viirscens is found to possess a good many more 

 fibers in its spinal nerves in proportion to its weight than the 

 European Rana esculenta, the species investigated by Birge. 

 This is not only true when the 6th. nerve is compared with the 

 6th. nerve of frogs of like weight, but also the numbers pre- 

 viously obtained for the greater number of the spinal nerves of 



