BEHAVIOR OF LOWER INVERTEBRATES 391 



By stroking gently various parts of the body of a snail in 

 much the same way as these parts are stimulated during the 

 mating activities Szymanski (47) has succeeded in evoking 

 reactions which closely simulate those of mating. The studies 

 of Szymanski (48) on the relation of tropisms to rapidity of 

 movement were made partly on insect larvae and partly on 

 leeches and earthworms. When the animals studied were in a 

 condition of relative inactivity they progressed with less rapidity 

 and made many trial movements in their sinuous course. When 

 more active they become oriented more directly and progress 

 with greater rapidity and in a straighter path. The author 

 discusses different interpretations of the relation of trial move- 

 ments to locomotor activity. 



Torrey (50) has given a discussion of the role of trial move- 

 ments in orientation, especially in the case of Euglena, which, 

 it is contended, contrary to the views of Jennings and Mast, 

 orients itself by direct responses to stimuli instead of by the 

 method of trial and error. 



Yung (51) has reached the unexpected conclusion that the 

 eyes of snails despite their considerable degree of development 

 are not light percipient organs. Other parts of the body, how- 

 ever, possess a photodermic sensibility. 



Zimmermann (52) describes the movements and respiratory 

 activities of the Galatheidea with especial reference to the 

 structural adaptations involved. 



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