60 RALPH EDWARD SHELDON 



IV. CONCLUSIONS 



The experiments and observations here recorded show that the 

 passage of a current of water through the nasal capsules of the 

 dogfish is necessary for the recognition of food substances and the 

 identification of their location. The nerve termini stimulated 

 by the food juices dissolved in this current are, with little ques- 

 tion, olfactory. Experiments performed on dogfish with the 

 olfactory crura cut, but with the mandibularis nerve intact, 

 show that such individuals do not react to food juices, but to 

 tactile and general chemical stimuli only. The function of the 

 nervus terminalis is unknown, but the number of its fibers is 

 very small and anatomically it gives no indication that it is of 

 special importance. It is, moreover, practically negligible in 

 the case of the teleostean fishes which react to the stimuli of food 

 substances in a closely similar manner (Parker, '10, '11). 



The statement is sometimes met with that the the function of 

 the olfactory apparatus of aquatic vertebrates can not be similar 

 to that of the terrestrial forms as in the one case the stimulating 

 substance is in solution in the water, while in the other it is float- 

 ing in the air. As all substances which the air breathing verte- 

 brates recognize by means of their olfactory apparatus must first 

 be dissolved in the moisture of the nasal mucous membrane, there 

 is no distinction between the two cases. 



Olfactory sensation differs from general chemical and from 

 taste in that the stimulating substances are in more dilute form; 

 it is, therefore, chiefly for the cognition of distant substances, 

 as Sherrington ('06), Herrick, ('08), and Parker, ('10) have pointed 

 out. It may then be stated that, on the evidence here submitted, 

 the olfactory apparatus of the dogfish reacts to substances in so 

 dilute a solution in the water that the taste buds and other organs 

 of chemical sense are not affected. The selachians, then possess 

 a sense of smell comparable to that of terrestrial vertebrates. 



