THE EARTHWORM AND ANNELIDS IN GENERAL 187 



where their bodies come in contact with solid objects; they 

 apparently like to feel the walls of their burrows against their 

 bodies or, when outside of their burrows, to lie or crawl upon the 

 ground (155). Reactions to sounds are not due to the presence 

 of a sense of hearing, but to the contact stimuli produced by vi- 

 brations. Darwin showed that musical tones produced no re- 

 sponse, but that the worms contained in a flower pot drew back 

 into their burrows immediately when a note was struck, if the 

 pot were placed upon a piano, this result being due to vibrations. 



CHEMOTROPISM. Contact is not sufficient to cause burrowing, 

 but a combination of mechanical and chemical stimuli seems 

 necessary at least this is true of the small earthworm, Allolo- 

 bophora fceiida, found in heaps of manure. A worm of this 

 species does not burrow when placed in contact with dry filter 

 paper; but immediately responds if the paper is wet with water 

 or liquid taken from manure. In certain cases chemotropic 

 reactions result in bringing the animal into regions of favorable 

 food conditions, or turning it away from unpleasant substances. 

 Moisture, which is necessary for respiration and consequently 

 for the life of the earthworm, causes a positive reaction, provided 

 it comes in contact with the body, no positive reactions being 

 produced by chemical stimulation from a distance. Negative 

 reactions, on the other hand, such as moving to one side or back 

 into the burrow, are produced even when certain unpleasant 

 chemical agents are still some distance from the body. These 

 reactions are quite similar to those caused by contact stimuli. 

 Danvin explained the preference of the earthworm for certain 

 kinds of food by supposing that the discrimination of edible from 

 inedible substance was possible when in contact with the body. 

 This would resemble the sense of taste as present in the higher 

 animals. Such a sense might account also for the positive 

 burrowing reaction cited above, which is caused by contact with 

 fluids from manure. 



Certain experiments in which animals were subjected to solu- 

 tions of sodium, ammonium, lithium, and potassium chlorides 



