Hadley, Behavior of the American Lobster, 299 



a. During the early first stage-period no intensity of light used 

 changes the index of the phototactic or of the photopathic response, 

 but later an intense light may reverse the index of the phototactic 

 reaction. 



b. Throughout the second and third stage-periods, the index 

 of the photopathic reaction is not reversible, but during the early 

 part of these periods the negative phototactic reaction, and dur- 

 ing the latter part the positive phototactic response, maybe reversed 

 temporarily by using light of great intensity (suddenly introduced). 



c. During the fourth stage-period the negative phototactic 

 response can not be reversed (except in such instances as are 

 noted in Exp. 24, Cases 5 and 6), but the positive photopathic 

 reaction of the early fourth stage-period may be reversed tempora- 

 rily by using light of very great intensity. 



d. None of the negative responses of the fifth-stage lobsters 

 can be reversed by using light of any intensity whatsoever. 



e. Submitting larvae to darkness for periods of 2 to 12 hours 

 does not change the index of reaction. 



4. The reactions to light can be modified by other factors; con- 

 tact-irritability is first manifested in the middle or later part of the 

 fourth stage-period, and henceforth determines (about equally 

 with light) the behavior of early adolescent lobsters. 



5. Laboratory experiments explain some of the aspects of the 

 behavior of the young lobsters under natural conditions of environ- 

 ment: (i) The positive photopathic reaction, and the positive 

 phototactic reaction (to lights of very great intensity) together with 

 the; '* jponse to food stimuli may unite in determining the surface- 

 swimming of the early fourth-stage lobsters. (2) The negative 

 photopathic reaction, the negative phototactic reaction together 

 with the response to contact-stimuli may unite in causing the 

 late fourth, fifth and all later-stage lobsters to leave the surface 

 water, and to burrow at the bottom of the sea. 



6. The reaction of larval lobsters to light depends upon two 

 factors; body-orientation and progressive orientation. 



7. The body-orientation is invariably negative and is due to 

 the difference in illumination of the two eyes of the larva. It is 

 brought about by invariable reflex movements which tend to 

 bring the longitudinal axis of the body parallel to the rays of light, 

 with the head away from their source. 



8. The progressive orientation may be either positive or nega- 



