KEACTIONS OF BRANCHIPUS TO EXTERNAL STIMULI 239 



two weeks, and opportunities for field observations considerably 

 lessened in consequence. The results obtained were so incomplete 

 that it has been thought best to confine this paper to an account 

 of the experimental work carried out in the laboratory. 



I am indebted to Dr. Charles F. Hottes, and Dr. Charles Zeleny 

 for many courtesies extended to me during the progress of the 

 work. Especially do I wish to express my gratitude to Dr. F. W. 

 Carpenter, under whose direction the work was carried on, for 

 his careful supervision and kind suggestions. 



SUMMARY 



1. Branchipus serratus is positively phototropic under the 

 influence of lights varying in intensity from 12 to 280 candle 

 power. 



2. After exposure to darkness, varying from twleve hours to 

 six weeks, the animals still respond positively to light. 



3. Light apparently has a kinetic effect which increases with 

 the intensity. 



4. When Branchipus reacts to light the ventral side of the 

 body is usually turned toward the source of light, with the long 

 axis of the body lying at right angles to the light rays. 



5. The eyes are the only sense organs capable of receiving the 

 light stimulus. 



6. Branchipus responds positively to temperatures of from 

 14° to 17° C, and avoids temperatures above or below this. Tem- 

 peratures as high as 28° C. are fatal. 



7. The animals are positively geotropic in light, and nega- 

 tively geotropic in darkness. 



