140 'Journal of Cojuparative Neurology and Psychology. 



the brain and cord of R. pipiens, so as to mask the effect of age 

 (size), but it is to be added that the disturbance thus produced is 

 relatively small, and not sufficient to affect the distinctive differ- 

 ences between R. pipiens and the species here compared with it. 

 If the average values for the percentage of water in the brain and 

 spinal cord of the three species are calculated from Table 13 we 

 obtain the following: 



TABLE 15. 



Average values for the percentage of water in the brain and spinal cord of all three 

 species, together with the difference between that for the brain and for the 

 spinal cord in each species, and the relative amount of water in the spinal cord, 

 that in the brain being taken as a standard. 



Percentage of Water 



Brain. 



Sp. Cord 



Differ- 

 ence. 



Percentage 

 Value of Cord 

 Determination. 



R. pipiens , 84 . 97 



R. esculenta 83.35 



R. temporaria 82. 17 



80.50 



78.55 

 77.62 



4-47 



4-55 



94-7% 

 94 ■^% 

 94-4% 



It appears from this table that the absolute differences in the 

 percentage values for the brain and cord are similar in the three 

 species, and that the determinations for the brain being taken as the 

 standards the relative values of the determinations for the spinal 

 cord are about alike, ranging from 94.2 per cent R. esculenta, 

 to 94.7 per cent R. pipiens. The similarity in these relations 

 speaks for the correctness of the general results. 



In this connection it is natural to enquire how the weight rela- 

 tions of the central nervous system or its parts, might be affected 

 if the percentages of water in R. esculenta and R. temporaria 

 were raised to that found in R. pipiens. Calculations have been 

 made, and the results show that the superiority of the entire cen- 

 tral nervous system and of the brain in Rana pipiens would be 

 diminished only slightly. On the other hand, the weights of all 

 the spinal cords would be brought together, and R. temporaria 

 given the heaviest cord. 



Moreover, in general, the weight values in the two European 

 species would be brought closer to one another. 



These alterations would however not essentially modify any 

 of the differences on which we have had occasion to lay emphasis. 



