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THE AMERICAN NATURALIST. [Vol. XXXVII. 



Parker has also shown that the lateral line organs of fishes are 

 sensitive to mechanical jars of low frequency. This again is 

 closely related to the tactile function and has doubtless given 

 rise phylogenetically to the power of perceiving rhythmic vibra- 

 tions of higher frequency, viz., hearing, a part of the sense 

 organs of the acustico-lateral system within the internal ear 

 having been set apart for this function in the course of verte- 

 brate evolution. 



Having now a morphological criterion for defining the cutane- 

 ous sense organs belonging to the lateral line system, it may be 

 stated briefly that all other specialized cutaneous sense organs of 

 fishes at present known may be grouped with the taste buds of 

 the buccal cavity both on the basis of their structure and of their 

 innervation. The nerve supply of all of these organs is now 

 known to be from a system of nerves distinct for their entire 

 extent from those previously considered, but intimately related 

 centrally to the sensory nerves from visceral surfaces in general. 

 This is known to students of nerve components as the communis 

 system of nerves and sense organs, because its fibers all end 

 centrally in the gray matter connected with the fasciculus 



This system of nerves, like the acustlco-lateralis, is well 

 developed in certain cranial nerves only, and, as the latter system 

 is supposed to have evolved from the general cutaneous system, 

 so the communis system has probably been differentiated from 

 the general visceral sensory nerves of the trunk. Peripherally 

 it is easy to distinguish the unspecialized component of this 

 system from that which is distributed to special sense organs ; 

 but centrally this is much more difficult. This, however, I think 

 I have accomplished in part at least in the case of Ameiurus. 

 At any rate, the chief ascending gustatory path in these fishes 

 is clearly separable from all other reflex paths from the primary 



No important distinction can be drawn either in structure or 

 in innervation between the terminal buds of the outer skin and 

 the taste buds of the mouth, and to complete our argument it 



function also. This has now been accomplished. In July, 1902, 



