PHYLUM ANNELIDA. SEGMENTED WORMS 



181 



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Figure 97. Earthworm cocoons deposited in cornstalk compost. Arrows point to cocoons. 

 (Photo courtesy of R.C. Ball.) 



with two tails; and an anterior piece may be 

 united with a posterior piece to make a 

 short worm. In such regeneration experi- 

 ments, the parts are held together by threads 

 until they become united. Regeneration 

 probably does not contribute to the survival 

 of the earthworm as much as it does to 

 planarians and starfishes. 



Behavior 



The external stimuli that have been most 

 frequently employed in studying the be- 

 havior of earthworms are those dealing with 

 contact, chemicals, and light. 



Reactions to mechanical stimuli 



Mechanical stimulation, if continuous and 

 not too strong, calls forth a positive reaction; 

 the worms live where their bodies come in 

 contact with solid objects; they respond to 

 the stimulus of mechanical contact such 

 as the walls of their burrows. Reactions to 

 sounds are not due to the presence of a 

 sense of hearing, but to the contact stimuli 



produced by vibrations. Darwin showed that 

 musical tones produced no response; but if 

 a flower pot containing earthworms was 

 placed upon a piano and a note was struck, 

 the worms immediately drew back into their 

 burrows. This result was due to vibrations. 



Reactions to chemicals 



In certain cases, reactions to chemicals re- 

 sult in bringing the animal into regions of 

 favorable food conditions or turning it 

 away from unpleasant substances. Moisture, 

 which is necessary for respiration and con- 

 sequently for the life of the earthworm, 

 causes a positive reaction, when it comes in 

 contact with the body; no positive reactions 

 are 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 reac- 

 tions are quite similar to those caused by 

 contact stimuli. Darwin explained the prefer- 

 ence of the earthworm for certain kinds of 



