128 'Journal of Comparative Neurology and Psychology. 



Table 5 shows that the value in question ranges in the fresh speci- 

 mens from 17.8 per cent to 16.2 per cent, and also tends to diminish 

 as the total length of the frog increases. The same relations 

 are shown in Table 6, in which all three species are represented, 

 and these form as satisfactory a series as is given in Table 5. 

 We therefore conclude that in this character — the relative 

 length of the entire central nervous system — the three species 

 resemble one another closely. 



It should be pointed out here that it follows from this that the 

 smaller weight of nervous system which w^e find in the European 

 forms (see below) must be associated with a diminution of one or 

 both the transverse diameters, since the foregoing shows that it is 

 not associated w^ith variations in total length. 



(9) In the arrangement of the main branches of the crural and 

 sciatic nerves (Dunn '00 and '02). In the papers to which ref- 

 erence is here made, this point is fully discussed. 



In view of the fact that the several species are similar in the 

 foregoing characters, w^e might expect a high degree of similarity 

 in the weight and structural relations of the central nervous sys- 

 tem. Such however is not the case, and we turn therefore to a 

 statement of the differences which have been observed. 



The technique of weighing, measuring and dissecting, was uni- 

 form for the three species. This has already been described 

 (Donaldson, '98, Donaldson and Schoemaker, 'go). 



It may, however, be well to repeat here that the body weight 

 was taken in a closed box; the weight of the contained ova being 

 deducted from the body weight of the unopened specimen, in the 

 case of the females. Also in both sexes correction was made for 

 the stomach contents. 



In taking the total length, the frog w'as suspended by the lower 

 jaw, and the distance between the tip of the nose and the longest 

 toe, the legs being fully extended, was measured with vernier 

 calipers. The central nervous system was removed immediately 

 after death, and the brain separated from the spinal cord by a 

 section at the level of the tip of the calamus scriptorius. Both 

 brain and cord were separated from their nerves by severing the 

 latter at the points of their attachments to the central structures. 

 To obtain the percentage of water, the material was dried for 

 several days until it maintained a constant weight. For this a 

 water bath ranging from 85° to 95° C. was used. 



