Art. v.] Hekrick, Size of Nerve Fibers. 35 



conspicuously in diameter and this is correlated with a similar 

 difference in the size of the muscle fibers innervated. 



I have observed many similar cases, especially among the 

 branchial muscles of fishes, whose fibers vary greatly in size, 

 depending apparently upon the functional importance of the 

 muscle in question. It is a general rule, though by no means 

 an invariable one, that in the fishes large muscle fibers are sup- 

 plied by large nerve fibers and conversely small muscle fibers 

 by small nerve fibers, irrespective of the relative length of the 

 nerve fibers. 



Now, to return to Miss Dunn's paper, she finds that 

 Schwalbe's inference, that, other things being equal, the long- 

 est nerve fibers have the largest diameter, does not hold true in 

 the case of the sciatic nerve of the frog. On the other hand, 

 the largest nerve fibers, it appears from her observations, are 

 given off with the branches for the thigh, while the shank and 

 foot are innervated by the smaller fibers. 



Now, if we confine our attention for the moment to the 

 motor fibers of the sciatic nerve, those for the muscles of the 

 thigh should be larger in diameter than those for the shank, 

 provided our rule stated above holds true, since the muscles of 

 the thigh are much larger and more important, functionally, 

 than those of the shank. 



But this peculiarity is not confined to motor fibers. In 

 the study of the innervation of the cutaneous sense organs of 

 fishes I have met with many analogous instances. Thus, the 

 organs of the lateral line system of fishes are usually inner- 

 vated by very large nerve fibers, the largest in the body. But 

 in many fishes a part of the organs of this system are greatly 

 reduced in size, and presumably in functional importance. That 

 these reduced organs are of small functional importance is 

 rendered still more probable by the fact that their essential 

 sensory cells, the hair cells, exhibit a greater proportional 

 reduction than the indifferent supporting cells. Now, these 

 reduced organs, irrespective of their position on the body and 

 hence of the length of the nerve fibers which innervate them, 



