198 University of California Publications in Zoology [Vol. 11 



PAGE 



VI. Special features of behavior in leeches 233 



1. Modification of behavior during breeding season 233 



2. Diurnal rhythmical behavior 240 



3. Behavior of the young leeches 241 



4. Operation experiments 245 



5. Function of the brain 248 



B. MoDiFiABiLiTY IN THE BEHAVIOR OF THE Leech Diua microstoma 



Moore. 



I. Introduction 250 



II. Different responses to the same stimulus 251 



1. Reactions to stimulation of the anterior end 252 



2. Order of response in twenty-five stimulations of the 



anterior end 254 



3. Reactions to stimulation of posterior end 256 



4. Determining factors of the different responses to the 



same stimulus 256 



(a) Intensity of stimulus 256 



(b) Localization of stimulus 257 



(c) Position of the body 257 



(d) Tonus of the organism 258 



(e) Chain reflexes 259 



III. Acclimatization to stimuli 261 



1. Acclimatization to repeated jars 261 



2. Acclimatization to successive shadows 263 



3. General discussion of acclimatization results 265 



IV. Normal fatigue from repeated contact stimuli 267 



V. Induced depression 272 



1. General methods 272 



2. Strychnine 273 



3. Nicotine 274 



4. Cocaine 278 



5. Chloretone 279 



6. Magnesium sulphate 280 



7. Carbon dioxide 282 



8. Mono-potassium phosphate 283 



9. Lactic acid 284 



10. Discussion of fatigue 284 



VI. Effect of combined stimuli 285 



1. Influence of food-juices on reaction to contact in 285 



(a) Normal individuals 285 



(b) Starved leeches 287 



(f) Well-fed leeches 288 



2. Light and contact 288 



VII. Influence of internal states 290 



1. Behavior of well-fed leeches 290 



2. Reactions of starved leeches 291 



3. Responses of undisturbed leeches 292 



VIII. General considerations on modifiability in leeches 295 



IX. Summary 297 



X. Bibliography 301 



