BEHAVIOR OF LOWER INVERTEBRATES 381 



formation varies in direct proportion to the number of trials. 

 The chief factors in the formation of this habit are sight and 

 touch, especially the former. The habit persists after a lapse 

 of ten days but it can be unlearned " although previous experi- 

 ence seems to have no influence on the rapidity of unlearning." 



Welch (37) in an extensive study of the Enchytraeidae of North 

 America gives a number of experiments on the reactions of 

 Lumbricillus rutilus n. sp. to a number of stimuli found in its 

 environment. As this species is found in one of the sewage 

 disposal plants of Chicago, the author gives a discussion of the 

 relation of the behavior of this animal with respect to the work 

 done by the disposal plants and concludes that the worms facili- 

 tate the oxidation of unstable organic matter and increase the 

 putrescibility of the sewage. 



Wilhelmi (38) gives a note on the function of the grasping 

 organ or sucking pit (Sauggrube) of fresh water triclads. 



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