NATURE OF SENSE ORGANS 15 



an eye or an ear, for instance, it should be accredited with 

 all the central nervous activities, sensations and the like, 

 that accompany such an organ in man, qualified only by 

 the degree of development to which the particular organ 

 in the given animal has arrived. Conclusions based 

 upon such a course of reasoning were commonly ad- 

 mitted as valid by the workers of a few decades ago 

 (Lubbock, 1882 ; Graber, 1884) and the text-books of that 

 period in dealing with the sense organs of the lower 

 animals discuss these parts ordinarily under the conven- 

 tional five heads of the older human physiology ( Jourdan, 

 1889). From this standpoint one of the lower animals is 

 like a defective human being in that its full sensory ac- 

 tivity falls short of that of the normal man. Or it may be < 

 compared to a person whose sensory development is un- ( - 

 symmetrical and whose relations with the surroundings 

 have come to be predominant through a limited number 

 of sensory channels rather than through all. 



It is likewise perfectly clear that a given animal, whose 

 organization in general may be simpler than that of man, 

 may nevertheless excede him in a particular sensory 

 capacity and in this respect at least stand above him. It is . 

 commonly admitted that the dog far outruns man in the . 

 keeness of his sense of smell and it has long been known 

 that cats hear tones of a pitch much too high for the human 

 ear. These and other like examples show that though the 

 senses of the lower animals are in general less efficient 

 than those of man, the reverse is occasionally true. 



Moreover among some of the lower forms, sense or- 

 gans have been discovered that are not represented in 

 man. Thus fishes possess, in addition to the five classes of 

 human sense organs, the so-called lateral-line organs. 



