Donaldson, American and European Frogs. 



137 



In addition to the several weights, a determination of the per- 

 centage of water was made in the case of both the brain and spinal 

 cord. The method has been described already on p. 128. 



The condensed results are given in Table 13. 



On putting the data in Table 13 in the form of curves (Chart 5) 

 it becomes evident at a glance that the percentages found in the 

 three species are different, and also that they follow the order of 

 the weight of the entire central nervous system and of the brain. 



90% r Percentage of ^valrer 



63% 



QO% 



75% 



Drain. 



R.p. 



^-^R.e. 



K.t. 



R.e. 



Body ^H^ei^Sit — 6 ms. 



10 



15 



20 



S5 



30 



35 



-10 



-15 



CHART 5. 

 Showing the percentage of water in the brain and in the spinal cord. 

 R. p. = Rana pipiens. 

 R. e. = Rana esculenta. 

 R. t. = Rana temporaria. 



These differences in a character in which we might expect a high 

 degree of similarity, call for some comment touching the trust- 

 worthiness of the results. 



First, as to R. pipiens; the percentages in this species are the 

 highest. The best evidence for their general correctness is fur- 

 nished by the following table, extracted from the unpublished 

 observations (1901) previously mentioned. At each date given 



