PHYSIOLOGY OF OLFACTION 67 



toward the side on which, the concentration of odorous 

 particles is greater. The certainty of this operation 

 would increase in proportion as the nostrils of a given 

 fish are separated one from the other laterally. A good 

 example of an animal in which this condition reaches 

 its maximum is seen in the hammerhead shark in which 

 the nostrils, as well as the eyes, are carried on the re- 



Tahle IV. 

 Records in per cent, of Turning Movements of three Dogfish under the follow- 

 ing successive Conditions: Normal, Left Nostril Occluded, Right Nostril 

 Occluded, Both Nostrils Open Parker, (1914). 



markable lateral projections that extend sidewise from 

 its head into the sea (Fig. 15). 



The turning response of dogfishes under the condi- 

 tions mentioned in the preceding paragraph has a 

 striking resemblance to !the circus movements in the 

 tropic reactions of many of the lower animals and, were 

 it not that fishes are so highly organized, it might be 

 accepted at once as a response of that kind. The detailed 

 condition of such reactions is well illustrated by the 

 records in Table IV. 



As a residt of the evidence thus far accumulated, it 

 seems quite clear, contrary to the opinions expressed by 

 Nagel and others, that many fishes scent their food much 

 as air-inhabiting animals do and that they must be re- 



