NERVOUS SYSTEM OF THE FROG 13 



three weeks after the assumed maximum, and at a time when the 

 seasonal weight has begun to diminish. Here the difference is 

 less than in the case of the esculenta, but is susceptible of a similar 

 explanation. 



The relation of these two series of observations can be conveni- 

 ently shown in still another way. 



I have been able to point out (Donalsdon '02) that a fairly accu- 

 ate determination of the weight of the central nervous system 

 in frogs can be made by the formula 



C. iV. S. = (Log. Bd. W. t}~L)C 



where C. A r . S. is the weight of the central nervous system, Bd.W. 

 the body weight in grams, L the total length in mm. and C. a 

 constant to be determined for each species. Since publishing 

 this formula I have found that the most convenient way of 

 expressing seasonal variations on the weight of the central ner- 

 vous system is by the variations in C. 



Applying this method to the series before us, and remembering 

 that the increase in the relative weight of the central nervous 

 system is measured by the increase in C, and vice versa, we obtain 

 the following: 



TABLE 11 

 To show the values of " C" for each of the several series 



AVERAGE QF 



BODY WEIGHT 



R. pipiens 1904 \ 



Average of 12 records / 



R. esculenta 1904 



Average of 8 records > 32 . 4 24 . 6 



First " weight group " omitted J 



R. esculenta 1909 



Average of 9 records \ 33 . 1 23 . 



Last " weight group" omitted J 



Difference 1 . 6 

 R. temporaria 1904 \ 

 Average of 12 records/ ' 



R. temporaria 1909 1 

 Average of 16 records) ' 



Difference 0.9 



