10 



HENRY H. DONALDSON 



TABLE 9 



Percentage mine of the length of the entire central nervous system — the total length of the 

 frog being taken as the standard 



(E) THE WEIGHT OF THE CENTRAL NERVOUS SYSTEM 



Turning now to the main character under consideration, the 

 weight of the central nervous system, the condensed records are 

 presented in table 10. 



When these data are put in the form of a chart, (chart 2) 

 several interesting relations between the observations of 1904 

 and those of 1909 at once appear. In the first place the later 

 records follow the same line as the earlier; second, the record for 

 each species in 1909 is somewhat less than in 1904, and as a con- 

 sequence still further below the records of 1904 for R. pipiens. 

 This result serves to establish the main conclusion, namely that 

 R. pipiens has a heavier nervous system than either of the Euro- 

 pean forms. The fact that the values for the weight of the cen- 

 tral nervous system in the European species as determined in 

 1909 are less than those determined in 1904, calls for a word of 

 comment. 



Some unpublished studies which are being made on R. pipiens 

 at the Wistar Institute relative to the change in the weight of 

 the central nervous system with season, indicate that in this 

 species the greatest weight is attained about the end of July. 



