CRANIAL NERVES 147 



rays of the pectoral fin which are mocUfied to serve as "feelers" in the 

 search for food on the floor of the sea. Somewhat similar filamentous 

 pelvic fins of the gourami, codfish, and several other teleosts are 

 abundantly supplied with taste buds with the usual functions and 

 nervous connections ('00, '03; Scharrer, Smith, and Palay, '47); but 

 the free pectoral fin rays of the gurnards have no taste buds, and yet 

 it has been shown (by the authors last mentioned) that these fin rays 

 are sensitive to the same sapid substances as are the cutaneous taste 

 buds of other fishes and that the reactions also are similar. These 

 authors, in tracing the central courses of the large nerves which supply 

 these free fin rays, find that these fibers have central connections 

 similar to those of the pectoral fins of other fishes, belonging, that is, 

 to the general cutaneous system. They do not enter the f. solitarius. 

 They present evidence also that some secondary fibers from these 

 general cutaneous centers connect centrally with the superior gusta- 

 tory nuclei of the isthmus and hypothalamus, just as do the true 

 gustatory fibers arising in the nucleus of the f, solitarius. This is in- 

 terpreted to mean that these nerves of general cutaneous chemical 

 sensibility are so specialized that they can serve typical gustatory 

 reactions, though they do not connect peripherally with taste buds. 



These observations seem to show that some peripheral fibers of the 

 general cutaneous system, without specialized receptive end-organs, 

 may acquire functions substantially identical with those of cutaneous 

 taste buds and that such fibers have central connections similar to 

 those from taste buds. It is evident that no rigid categories can be 

 recognized here in terms of our conventional classification of "the 

 senses" or of their organs, a principle illustrated also by Whitman's 

 ('92) observations on the cutaneous sense organs of the leech, 

 Clepsine, to which reference is made on page 84. Nature is not 

 bound by our rules of logical analysis. 



Taste buds within the mouth are interoceptors, but similar buds in 

 the outer skin of fishes are typical exteroceptors, used in the selection 

 and location of food, as are also the free nerve endings of the general 

 cutaneous nerves that respond to chemical excitants. It is evident 

 that all these nerve endings co-operate with the nerves of ordinary 

 tactile sensibility in the normal process of finding food. That this co- 

 operation is intimate and in some cases indispensable has been shown 

 by Parker ('12) in the case of the catfish, Ameiurus. In this fish the 

 skin has general chemical sensitivity to acid, alkali, and salt, a 

 sensitivity which is served by general cutaneous nerves. In the skin 



