GENERAL CONCLUSIONS. 263 



very intimately related and he considers them but parts 

 of a single system. The commtinis centre, however, is 

 sharply separated from these, and he regards the latter sys- 

 tem as related to entodermal structures, as distinguished 

 from the two former which are related to ectodermal 

 structures. These are undoubtedly related mainly, if not 

 exclusively, to ectodermal sense organs, and it is quite 

 possible that the acustico-lateralis was differentiated from 

 the general cutaneous; but the communis system cannot 

 in the existing Ichthyopsida be regarded as related even 

 chiefly to entodermal structures. The taste buds them- 

 selves lie mainly, and probably wholly, in the region of 

 the stomodaeum, while the terminal buds of the outer 

 skin, which are undoubtedly innervated from this system, 

 are of course ectodermal. 



It is probably true that the communis system is 

 descended from a system of visceral nerves which was 

 primarily related to entodermal mucous surfaces and that 

 it has only secondarily encroached upon the ectoderm of 

 the stomodaeum and of the outer skin. These ectodermal 

 surfaces have also retained their proper nerve supply from 

 the trigeminus. This is illustrated by such pathological 

 cases as that of Adolf Schmidt ('95), where the visceral 

 sensation (taste) of the anterior two-thirds of the tongue 

 was totally lost, but tactile sensation not so profoundly 

 affected. 



Section 13. — Conclusions. 



I. — General. 



In addition to this general review, a summary will be 

 found at the close of each of the sections and to these the 

 reader is referred for the chief anatomical and morpho- 

 logical findings. 



