194 'Journal of Comparative Neurology and Psychology. 



CONCLUSIONS. 



In the leopard frog, Rana pipiens, we have found: 



1. The average length of the internodes on the fibers in the 

 nerves to the leg diminishes towards the periphery. This diminu- 

 tion is accompanied by a corresponding diminution in the average 

 diameter. 



2. In the same frog, the length of the internodes at different 

 levels on fibers of like diameter in the nerves to the leg, increases 

 toward the periphery. This increase appears to be associated 

 with the more rapid growth of the distal segments of the leg, but 

 the influence of the segment on the portion of the nerve within it, 

 is less marked as the frogs become larger. 



3. When the average length of the internodes on fibers of a 

 given diameter is compared w^ith the average length on the fibers 

 which represent them in a larger frog, it is found that the lengthen- 

 ing of the internodes corresponds with that of the nerve to which 

 they belong, thus supporting Boycott's ('04) general conclusion. 



4. In the roots of the IX spinal nerve, the internodes lengthen 

 in proportion to the lengthening of the nerve, but at the same 

 time, the lengthening of these roots is only loosely correlated with 

 the increase either in the total length or in the body length of the 

 frog to which they belong. 



5. When, in the same frog, the ventral root of the III nerve is 

 compared with the ventral root of the IX nerve, it is found in both 

 of them, that the fibers of the same diameter have internodes of 

 the same length. In the case chosen, the ventral root of the IX 

 nerve had become 2.7 times the length of the III nerve and we 

 should therefore expect to find the internodes on the fibers of the 

 IX nerve much longer than those on the corresponding fibers in the 

 nerve III. The explanation of this result awaits further observa- 

 tions. 



6. A determination of the number of medullated nerve fibers 

 at the level of the knee and of the ankle in a series of tadpoles' legs 

 of increasing length, shows that the relative number of medullated 

 fibers at the ankle, increases as the leg becomes longer, thus prov- 

 ing that the fibers to the more distal divisions of the limb are 

 medullated later. 



7. It follows from the foregoing result that so long as the nerve 

 receives new (young) fibers, there will always be internodes which 



