88 Bulletin of Laboratories of Denison University [voi. xii 



case, though the organs of vision are not necessarily modified, 

 these organs are actually used in procuring food, the fish being 

 unable to effect visual reflexes toward food substances or to cor- 

 relate visual stimuli with the movements necessary to react to- 

 ward food substances. The fish may be perfectly able to effect 

 other visual reflexes, but is apparently unable to understand the 

 significance of food when perceived by the sense of sight only. 

 This particular central reflex path has never been developed, or 

 has atrophied from disuse. Nature has here effected for the 

 species something similar to what is accomplished in individual 

 men occasionally by disease, in the production of certain 

 aphasias. 



The number of reflex activities habitual to an animal with 

 a nervous system as simply organized as the bony fish is proba- 

 bly far smaller than is commonly supposed, and these activities 

 are in general characterized by but little complexity of organi- 

 zation. It is probably quite within the range of possibility to 

 determine by observation and experiment for any given species 

 of fish to a high degree of accuracy what these habitual activi- 

 ties are and to work out by histological methods the reflex arc 

 within the nervous system for each of them ; and since the hu- 

 man nervous system is built up on the same general plan as the 

 piscine nervous system it follows that such a thorough and sys- 

 tematic correlation of function with structure would be profita- 

 ble from many points of view. 



Terminal buds do not occur in the outer skin of all fishes ; 

 in fact, they are probably lacking here in the greater number 

 of species. But whenever they do occur they tend to be ar- 

 ranged according to one general plan. This is particularly true 

 of their nerve supply, for, though the details of the peripheral 

 nerves of fishes are exceedingly diverse, yet the main communis 

 branches for terminal buds, when such occur, are substantially 

 similar from the Siluridae to the Gadidae. There are, however, 

 striking resemblances in detail between the siluroids and the 

 cyprinoids which are much more significant of close relation- 

 ship. Both groups are characterized by an extreme develop- 

 ment of the system, reaching generally over the whole body 



