Donaldson, American and European Frogs. 



131 



TABLE 10. 

 Weight of the central nervous system in grams, averages from groups of three. 



R. pipiens. 



R.esculenta. 



R. temporaria. 



The data in the foregoing tables are also presented in Chart 2 

 and the relations are more easily discussed by reference to the 

 chart, which shows R. pipiens to have the heaviest central nervous 

 system, R. esculenta the next heaviest, and R. temporaria the 

 lightest. 



By measuring the differences between the several entries for 

 the two European species, and the corresponding points on the 

 curve for R. pipiens, which is taken as the standard, it appears 

 that on the average, the central nervous system of R. esculenta 

 weighs about 89 per cent, and that of R. temporaria 88 per cent, 

 of that found in R. pipiens. 



It is known that dry air and starvation (Donaldson '98, Don- 

 aldson and ScHOEMAKER '00) tend to reduce the weight of the 

 living frog, and probably of the central nervous system, also that 

 the weight of the latter is increased in frogs which are mori- 

 bund, and have consequently taken up an excessive amount of 

 water. 



There is no reason to think however that the foregoing obser- 

 vations are seriously modified by any of these influences. 



Moreover unpublished observations on R. pipiens, in my pos- 

 session, indicate a variation in the weight of the central nervous 

 system with season. Nevertheless from the middle of June to 

 the middle of September, such variations as occur, are hardly 



