Donaldson, American and European Frogs. 123 



versity of Chicago. It is the results of these three series of obser- 

 vations which are now to be compared. 



As the foregoing shows, this investigation was undertaken 

 primarily to test the correctness of Fubini's observations. It 

 has resulted however in bringing to light several differences be- 

 tween the nervous systems of the species compared, and these 

 differences seem worth recording. At the same time, Fubini's 

 observations have been found untrustworthy. This, however, 

 is a matter of small importance, and the brief discussion of Fubini's 

 work will be deferred to an appendix. 



Before presenting the data on the nervous system, it will be 

 desirable to record some of the characters in which these three 

 species of frogs closely resemble one another. The resemblances 

 important for our present purpose are enumerated below: 



(i) In external appearance and shape; color markings excepted. 



(2) In the range in body weight (the heaviest specimens are 

 always females). 



(3) In the ratio obtained by dividing the body weight by the 

 total length, that is, the average amount of body weight for each 

 running millimeter of total length. 



It will be necessary to interrupt the enumeration for a moment 

 in order to elaborate this point (3). 



In the full tables are given the body weight and the total length 

 of each individual examined. In the condensed Table 10, these 

 same data are arranged to give the averages for groups of three. 

 Thus for each species in the latter table there are four entries, 

 and in each entry both the average body weight and the average 

 total length are given. If the former be divided by the latter 



Body weight 

 Total length 



we obtain a number which represents the average amount of 

 weight for each running millimeter. Since the increase in body 

 weight is more rapid than the increase in total length, this value 

 of course changes with the absolute weight of the frog, increasing 

 as the frog becomes absolutely heavier. The values thus obtained 

 are given in Table i. 



These values are better understood when thrown into a curve, 

 as in Chart i. 



It appears from the chart that the curves are nearly parallel, 



