48 Journal of Comparative Neurology and Psychology. 



in the nerves of the frog with those in a mammal, the figures ob- 

 tained by Hatai ('02 and '03) for the white rat are compiled and 

 arranged in the same way in the accompanying Table V. Hatai 

 also used but three nerves. So far as I know his results are the 

 only available for such a comparison. In both tables the num- 

 bers apply to the nerves of one side of the body only and 

 therefore must be doubled for the approximate numbers for both 

 sides. 



In the first place, it is further shown in Table IV that the 

 average younger frog possesses a good many more cells than fi- 

 bers in proportion to its weight than the older. It was shown in 

 the previous papers that the younger gain fibers at a more rapid 

 rate than the older. This is not so evident in the three nervgs 

 used here from the fact that the IXth nerves of the younger 

 contain considerably above the usual relative proportion of fibers 

 and thus produce larger sums for the three nerves. In the rat 

 Hatai finds that the gain in the younger is considerably more 

 rapid than in the older. 



It is also shown in Table IV (col's. B, C, D and E) that as 

 the frog increases in weight, for each gram of weight gained, 

 there is an apparent gain of 1 1 dorsal root fibers, i 2. 2 ventral root 

 fibers, 30.7 fibers in the trunks and dorsal branches and 10.4 

 fibers in the dorsal branches alone. Compared with results ob- 

 tained in a similar way from Birge's figures, such gains in only 

 three of the nerves of one side appear rather high. However, 

 as was previously seen ('00), Rana virescens seems to possess 

 an appreciably greater number of fibers in its spinal nerves in 

 proportion to body weight than does the European Rana esai- 

 lenta employed by Birge and therefore to maintain this, its ab- 

 solute gain of fibers per gram of weight gained must be 

 greater. 



It is also evident that apparently the ventral root gains 

 fibers at a somewhat more rapid rate than the dorsal root, the 

 relations being 1 2. 2 to 11 per gram gained. In the previous paper, 

 in the Vlth nerve alone, the advantage seemed to be with the 

 dorsal root, the ventral root gaining but 1.4 fibers to 2.4 gained 

 by the dorsal root. Computations from the figures available 



