1913] Gee: Behavior of Leeches 299 



14. Glossiphonia and Dina are able to undergo successfully 

 only a very slight degree of desiccation. 



15. Glossiphonia stagnalis and Dina microstoma are herma- 

 phroditic, fertilization taking place by means of a hypodermal 

 impregnation with spermatophores. Dina lays its eggs in a 

 cocoon after the manner of the earthworm. The eggs of G. stag- 

 nalis are carried attached to the ventral surface of the body, as 

 are also the young upon hatching. 



16. In the behavior of G. stagnalis, no presence of an "incu- 

 bation instinct ' ' seems to be evidenced. The adults show no signs 

 of a "parental" instinct; they carry their young only because 

 the small leeches are very persistently and strongly thigmotactic. 



17. Both Glossiphonia and Dina are active mainly at night, 

 and during the day remain underneath stones or in the less 

 lighted portions of the aquaria. 



18. The young of Glossiphonia stagnalis exhibit behavior 

 essentially the same as that of the adults. The chief difference 

 is the intensified positive thigmotaxis of the juvenile forms. 



19. The chief function of the brain in the leech appears to 

 be production of spontaneity of movement. There is in the de- 

 capitated specimens a marked decrease in the number of inter- 

 nally initiated movements. 



B. MODIPIABILITY IN THE BEHAVIOR OF THE LeECH 



Dina microstoma Moore 



20. The behavior of the leech is eminently modifiable, the 

 reaction at any one moment representing the resultant of many 

 concurrent stimuli, internal as well as external. 



21. Contact stimulation of the anterior end, of relatively 

 uniform intensity and applied to a particular part, produces 

 several dififerent types of response. The determining factors in 

 this variable behavior in the leech appear to be the intensity and 

 localization of the stimulus, since these can be only approximately 

 regulated, the position of the body at the time of stimulation, 

 the tonus of the organism, and the sequence of the reaction in 

 the chain reflex involved. 



22. The leech acclimatizes readily to slight shocks and shadows 

 repeated at thirty-second intervals. This acclimatization does 



