Takahashi, Internodes on Nerve Fibers. 193 



It is shown then that the medullation of fibers going to the 

 shank, the more proximal segment of the Hmb, is more nearly 

 complete than that of those passing to the foot, the more distal 

 segment, and probably the greater part of this difference depends 

 upon the fact that many of the fibers destined for the foot are not 

 medullated at all. 



This result, taken in conjunction with those of Hardesty ('99) 

 on the nerve roots of the frog, and Hatai ('01, '02), on the nerve 

 roots of the rat, indicates very clearly that new medullated fibers 

 are continually being added to the nerves during the period of 

 growth. 



5 a comparison of the length of the internodes in 

 the american leopard frog, rana pipiens, with their 



LENGTH IN THE ENGLISH FROG, RANA TEMPORARIA (FUSCA). 



In his Study, entitled "The nervous system of the American 

 leopard frog, Rana pipiens, compared with that of the European 

 frogs, Rana esculenta and Rana temporaria (fusca)," Dr. Don- 

 aldson ('08) compared the measurements of the internodes made 

 by me on Rana pipiens, with those made by Boycott on Rana 

 temporaria. Taking the same locality in both cases, and reduc- 

 ing the measurements on R. pipiens so that they apply to frogs of 

 the same total length as those measured by Boycott, a series of 

 values was obtained for seven diameter groups. It appeared from 

 a comparison of the results (see Donaldson '08, p. 146, Table 19), 

 that the internodal lengths in Rana pipiens, ranged between 64 

 and 71 per cent of those found in Rana temporaria, the average 

 being 67 per cent. 



The comparison appears to be a fair one, and if this is granted, 

 it is evident that Rana pipiens has on its fibers three sheathing 

 cells, where Rana temporaria has two. This result further draws 

 attention to the fact that the character in question is subject to 

 considerable variation, and that this appears not only in forms 

 widely separated zoologically, but also within the genus Rana, at 

 least in the case of the two closely related species here compared. 



