l6o 'Journal of Comparative Neurology and Psychology. 



His argument for the absence of smell m all aquatic anim^als is 

 based upon the definition of smell as the perception of gaseous or 

 vaporous stimuli. He adduces evidence that when air is dis- 

 solved in water it is incapable of absorbing the vapors given off by 

 volatile substances unless these vapors are soluble in the water 

 itself, stating that they cannot be dissolved in the air contained in 

 the water. They affect the organs, therefore, as true solutions, 

 not as gases dissolved in water. He says (p. 60), "All substances 

 which pass over into water from an object lying in the water, say a 

 decomposing organic body, diffuse themselves in the water in 

 accordance with the laws of the diffusion of liquids, not those of 

 gases and vapors, even though the object in question when brought 

 into the air may have vaporous emanations." 



It is unnecessary to summarize here his elaborate argument lor 

 the absence of smell in fishes based upon anatomical differences 

 in the receptive olfactory organs between fishes and air breathing 

 vertebrates; for when examined closely in the light of our present 

 knowledge these differences are seen to be trifling when com- 

 pared with the broad resemblances of both peripheral and central 

 organs of smell throughout the whole vertebrate phylum. 



Nagel's conclusion is expressed on p. 62: "We can with the 

 greatest probability assume that the end-buds of the glossopharyn- 

 geus in the mouth of fishes and amphibians serve the chemical 

 sense, viz: taste, and thus function in eating. We can with some 

 probability assume that the sense organs of fishes and aquatic 

 amphibia supplied by the N. olfactorius likewise serve the chem- 

 ical sense; but this is certainly no olfactory organ in the sense of 

 that term in the land animals. What the occasion of its chem- 

 ical excitation may be is quite unknown. The method by which 

 it is excited is with highest probability similar to the excitation of 

 the taste buds in the mouth, i. e., the excitation follows through 

 substances dissolved in water." 



This conclusion, to my mind, simply illustrates the fact that it 

 is impossible in the present state of our knowledge to interpret 

 these two senses in terms of the physical stimuli. It is not meant 

 to imply that there is no difference between the physical stimuH 

 of smell and taste; for I think it probable that further research will 

 bring such differences to light. But these differences are appar- 

 ently very small in aquatic animals, whereas the structural differ- 

 ences between the nervous apparatus involved are very great 

 indeed, even in the lowest fishes. 



