298 'Journal of Comparative Neurology and Psychology. 



Wickford, Rhode Island, where exceptional facilities were found 

 for obtaining material of all ages and stages. The writer's thanks 

 are especially due to Prof. A. D. Mead of Brown University for 

 making possible an opportunity for this line of inquiry and for 

 material assistance; to Dr. R. M. Yerkes of Harvard University, 

 and to Dr. H. E. Walter of Brown University for friendly criti- 

 cism during the preparation of the paper; also to Mr. E. W. 

 Barnes, Superintendent of the Wickford hatchery, for many kind- 

 nesses. 



VIII. summary. 



1. Larval and early adolescent lobsters present both photo- 

 tactic and photopathic reactions as these responses are defined on 

 p. 201. 



2. There is no constant type of response for all larval lobsters, 

 but a modification of reaction occurs through the metamorphosis 

 of the larvae. 



a. First-stage larvae, directly after hatching, give definitely 

 positive phototactic and photopathic reactions which endure for 

 about two days, after which the phototactic reactions change to 

 negative, becoming positive again shortly before moulting into 

 the second stage. 



b. Both early second-stage and early third-stage larvae mani- 

 fest a negative phototactic reaction, which usually becomes posi- 

 tive shortly before moulting into the third and fourth stages, 

 respectively. 



c. The photopathic reaction of the first three larval stages is 

 commonly positive from the beginning to the end of the stage. 



d. The phototactic reaction of the fourth-stage lobsters is usu- 

 ally (i. e., except in cases where intense light is used in connection 

 with early fourth-stage lobsters) negative throughout the stage- 

 period, and the photopathic reaction, positive during the early 

 fourth stage-period, eventually becomes negative. 



e. During the fifth stage-period, and in all later stages, both 

 the phototactic and the photopathic reactions are strongly nega- 

 tive. 



3. While the photopathic reaction of the larval lobsters re- 

 mains constant, the phototactic reactions are subject to modi- 

 fication as a result of changes in the intensity or in the direction of 

 light. 



