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THE AMERICAN NATURALIST [Vol. XLY1 



My own experiments indicate that in nature the cray- 

 fish will retreat from a strong light, but will approach a 

 dim one. In the spring I found that it was extremely diffi- 

 cult to frighten a crayfish from its food by means of my 

 acetylene light. In collecting at night it is very easy to 

 attract crayfish from some distance by setting a light on 

 the bank so that it dimly illuminates some little space of 

 water. 



Smell and Taste.— Very little experimental work to 

 determine the senses of smell and taste in any of the Crus- 

 tacea was done until Bell, in 1906, tested the reactions of 

 the crayfish (15) to chemical stimuli, applying meat juice 

 by means of a fine pointed pipette to various parts of the 

 body. He found that the antennae, antennules, mouth 

 parts and chelipeds were especially sensitive. 



Recently (1910) Holmes and Homuth published the 

 results of an extended series of experiments on crayfish 

 in which the outer or inner rami of the antennules were 

 removed; the antennules were removed entirely; the 

 antennae were removed; the chelipeds removed; and in 

 some specimens the brains were destroyed. (33). 



They found that the outer rami of the antennules bear- 

 ing the olfactory setae were especially sensitive to 

 olfactory stimuli, that the inner rami of the antennules, 

 the antennae, the mouth parts and the tips of the chelipeds 

 were all sensitive to some extent to olfactory stimuli. 



It is probable that in the crayfish we have a very highly 

 developed topochemical sense, or contact-odor sense. 

 Forel uses this term (25) in speaking of the fact that in 

 ants, odors are apparently detected by the contact of the 

 antennae. 



Bell found that the crayfish was sensitive to food when 

 not in contact with it. I experimented with freshly cut 

 meat and with meat which had been exposed to the air for 

 some time so that the cut surfaces had dried, and found 

 that the crayfish would go toward and seize the fresh meat 

 first. Evidently the diffusion of the meat juices was 

 readily detected. 



