298 University of California Publications in Zoology [Vol. 11 



3. Random movements or the tendency to "prove all things, 

 hold fast that which is good," constitute perhaps the most signifi- 

 cant single feature of leech behavior. 



4. Dima microstoma moves forward by the looping or the 

 swimming type of response. Glossiphonia stagnalis and Hemi- 

 clepsis occidentalis Verrill have their body structure modified 

 for carrying their young. It is perhaps for this reason that they 

 do not possess the swimming type of locomotion. 



5. Rhythmical undulatory movements in leeches seem to per- 

 form a respiratory function. Perhaps to a certain extent they 

 also exercise an accessory excretory function. 



6. There is a marked tendency for the leeches Glossiphonia 

 stagnalis and Dina microstoma to collect in groups. The deter- 

 mining factors in this group formation are the thigmotactic 

 propensities and negative phototaxis. 



7. To a large extent Dina microstoma appears to be a scaven- 

 ger; for it feeds upon dead fish, crushed snails [Limnea, Physa, 

 Plan or his) , recently killed crayfish, and similar food. Glossi- 

 phonia stagnalis was kept in good condition by feeding it small 

 living earthworms. 



8. Leeches are very sensitive, showing marked responses to 

 various light stimuli. Care must be exercised if such behavior 

 is to be observed. 



9. Both DitM microstoma and Glossiphonia stagnalis are nega- 

 tively phototactic. A strong light intensity produces a greater 

 initial number of random movements than does a low candle 

 power light, and appears to exert a more decided orienting effect. 



10. The nephelid is positively rheotatic. This reaction serves 

 to keep it in its breeding locality. 



11. To localized injurious chemical stimuli Dina microstoma 

 shows a decided negative response. The diffusing juices of a 

 snail produce a positive reaction. 



12. Super-optimum temperatures produce a greater degree 

 of activity, accompanied by an accentuation of the tendency to 

 perform random movements. 



13. Positive thigmotaxis is shown in the collections of leeches 

 underneath stones, in their reactions to food, and to a certain 

 degree to slight contact stimuli. Negative reactions are given 

 to localized contact, heat, and chemical stimuli. 



