698 Journal of Comparative Neurology and Psychology. 



While individual variation must receive due consideration, a more 

 definite argument for the dropping out of efferent medullated nerve 

 fibers from the unoperated leg of frog E is found in the decrease 

 in the number of nerve fibers in the IST. ischiadicus at successive 

 levels in the right thigh. This point will be taken up in detail in 

 the next section. 



Discussion of the Loss op a Small JSTumber of Efferent Medul- 

 lated ISTerve Fibers from the Unoperated Leg of Frog E. 



A comparison of the observed number of medullated nerve fibers 

 with the estimated number of medullated nerve fibers was made for 

 the thighs of frog B and of frog C, Dunn, 1900, and of frog IIB, 

 Dunn, 1902, and for the shanks in frog IIB, Dunn, 1902. In the 

 six thighs of these three frogs the excess of observed over estimated 

 medullated nerve fibers varied from 6 per cent to 10 per cent of the 

 number of observed nerve fibers. The numbers in the two thighs 

 of any one frog varied, however, in no instance by more than 1 per 

 cent, thus for frog IIB, Table X, the percentage excess for the left 

 thigh is 9 per cent, for the right thigh 10 per cent ; for the left 

 shank 21 per cent, for the right shank 22 per cent. We see that, 

 while the percentage excess in any segment varies considerably in 

 successive frogs, in any one frog the percentage excess varies but 

 slightly for corresponding segments in the two legs. This was to be 

 expected since in any frog the counts for any level vary but slightly 

 for the two legs. 



Let us now consider the conditions found in frog E, as shown in 

 Table IX. We find that on the operated side with only afferent 

 nerve fibers the percentage excess is approximately the same as that 

 for both legs of frog IIB, showing 10 per cent for the thigh and 28 

 per cent for the shank. In the supposedly intact leg the percent- 

 age excess is much less than on the operated side, being 6.5 per cent 

 for the thigh and 16 per cent for the shank. This percentage dis- 

 parity might be explained by the presence of a relatively larger 

 number of splitting nerve fibers on the operated side among the 

 afferent nerve fibers remaining there, than in the unoperated leg 

 where afferent and efferent nerve fibers are both present, were it 



