266 NERVE COMPONENTS OF BONY FISHES. 



of the voluntary muscles of the somatic series; and in 

 correlation with this modification, we find that their nerve 

 fibres, though quite certainly belonging to the viscero- 

 motor series, are of large size, like the somatic motor 

 nerves. Even among the somatic motor nerves it is a 

 general rule that small muscle fibres are innervated by 

 smaller nerve fibres than are larger muscle fibres. This is 

 illustrated best in the eye-muscle nerves, but frequently 

 also in the general somatic musculature. Among the 

 sensory nerves, too, the size of the fibres seems to depend 

 somewhat upon the state of development of the sense 

 organ to be innervated. Thus, while the canal organs of 

 the lateral lines are always supplied by very large fibres 

 with wide sheaths, when the canals disappear and the 

 organs lie exposed on the skin, as in a portion of the infra- 

 orbital line and in the main line of the trunk, these organs 

 are usually smaller than those in the canals, and are 

 supplied by smaller nerve fibres. And particularly the 

 lateralis fibres which supply the small naked organs of 

 the " pit-lines " are always of medium or even small size, 

 though they have the characteristic very densely stained 

 sheaths, so that they can be easily distinguished from 

 general cutaneous fibres of the same size. And, again, 

 the communis fibres, though very small when distributed 

 to visceral surfaces or taste buds on mucous surfaces, may 

 become somewhat larger and more heavily myelinated 

 when they distribute to large terminal buds of the outer 

 surface of the body, so that it is sometimes impossible to 

 distinguish them from lateralis fibres for the "pit-organs." 

 This, however, is not always the case, for in sections of 

 the siluroids and cyprinoids, where the terminal bud 

 system is much more highly developed than it is in 

 Menidia, I find these organs innervated by the very fine 



