348 Journal of Comparative Neurology. 



Rana virescens are found greatly to exceed per gram of weight, 

 the numbers given by Birge. 



That Rana esculenta has a smaller nervous system in pro- 

 portion to its body-weight than Rana virescens has been shown 

 in another way. Fubini ('8i) made a large number of weighings 

 for both R. esculenta and R. temporaria. His tables compare 

 the weight of the entire central nervous system with the body- 

 weight, and also the brain weight with the body weight. Donald- 

 son and Schoemaker ('oo) made a series of weighing and meas- 

 urements for R. virescens. When the proportions between the 

 body-weight and the weight of the brain and spinal cord ob- 

 tained by them for R. virescens are compared with Fubini's 

 results for R. esculenta, it is found that R. esculenta has a con- 

 siderably lighter central nervous system in proportion to its 

 body weight than R. virescens. Although as shown by Don- 

 aldson and Schoemaker, the weights for the spinal cord obtain- 

 able from Fubini's tables are somewhat large, yet the weight of 

 the cord alone in proportion to body-weight is less for R. escu- 

 lenta than for R. virescens. Fubini's tables show that R. tem- 

 poraria also has a relatively heavier central nervous system than 

 R. esculenta. 



The relations between the weight of the frog and the num- 

 ber of fibers contained in its 6th. nerve alone may prove of 

 some interest. 



Table IV groups the seven smaller specimens ranging from 

 4.7 to 10.7 grams against the five larger ranging from 48.2 to 

 78.8 grams. For each specimen is given in separate columns, 

 the number of fibers in each of the roots and the number on 

 the distal side of the spinal ganglion. In order to get the aver- 

 age number of fibers for each gram of weight, the sums of the 

 fibers for each of the roots and for the trunk are divided by 

 the sum of the weights of the specimens in each group. The 

 table also gives the number of fibers the average frog of each 

 group would possess in its 6th. spinal nerve of one side. 



