52 KALPH EDWARD SHELDON 



buds on the outer surface of the body, particularly on the barbels 

 and about the head (Herrick, '03), use these organs in the cog- 

 nition of food substances in contact with them. The sense of 

 taste must, therefore, be taken into consideration. 



Sheldon ('09), finds that the reactions of the nasal apparatus 

 to essential oils and to a number of other irritating substances, 

 is due to stimulation of the mandibular nerve and not the olfac- 

 tory, as was supposed by Nagel ('94). Sheldon also shows for 

 Selachians, as Parker ('08), had earlier pointed out for Ameiurus, 

 that the general cutaneous nerves react generally to many sapid 

 substances. This may easily explain the refusal of fishes to eat 

 food covered with essential oils (Aronsohn, '84). A general 

 chemical sense is, therefore, to be accounted for. 



Negative results after operations, such as the refusal of Scyllium 

 to eat after destruction of the olfactory crura or lobes (Steiner, 

 '88), are valueless, without the proper controls, as the shock of 

 the operation may easily so disturb the fish as to prevent feeding. 

 That this is likely to be the case is indicated by experiments car- 

 ried out in connection with this investigation, where it was found 

 that Selachians are extremely sensitive, so far as their feeding 

 habits are concerned, to any interference with their normal life 

 or environment. Physiological evidence regarding the function 

 of the olfactory apparatus of aquatic vertebrates has then, until 

 very recent date, been negligible. It is also clear that the ability 

 of such an animal to recognize food at a distance does not neces- 

 sarily mean the use, therefor, of the sense of smell. 



Anatomists and neurologists, struck by the constancy and size 

 of the nasal apparatus of fishes, as well as by the complexity and 

 long phylogenetic history of the nervous mechanism by which 

 it is brought into relation with the different parts of the brain, 

 have long believed that it must be an apparatus of paramount 

 importance in the life of the individual, particularly with respect 

 to the recognition of food substances (see Johnston, '06). 



In the last number of volume 8 of the Journal of Experimental 

 Zoology, appears an article by Parker, recording for the first 

 time, in the Siluroid, Ameiurus nebulosus, reactions unquestion- 

 ably due to stimulation of the olfactory apparatus. He finds that 



