240 ^Journal of Comparative Neurology and Psychology. 



the larval lobsters manifest a type of behavior which includes 

 widely varying kinds of reaction, even to the same stimulus. The 

 point has been, not to learn what reaction the lobster larvae give 

 to light, but to ascertain the conditions which so play upon the 

 mechanism of these organisms as to produce the wide i ange of 

 responses observed. The causes of the daily and the hourly vari- 

 ations in the kinds of reactions manifested by organisms is a field 

 which is, even at the present day, largely given up to speculation, 

 and all sorts of explanations have been brought forward from the 

 view of the rhythmical succession of certain movements resulting 

 from purely internal stimuli, to the view of cycles of change in 

 certain metabolic products under the influence of external stimu- 

 lation, and their consequent reaction upon the nervous processes 

 of the organism. The fact of variations in the reactions of larvae 

 of the European lobster (Homarus vulgaris) has been noted by 



Days 1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526272S29303132 



Phototactic 



Photopathic — 



Fig. 6. Diagram recapitulating the nature of the phototactic and photopathic reactions of lobsters 

 in the first five stages. The dotted line in the upper series indicates that the early fourth-stage lobster 

 may give a positive phototactic reaction to light of very great intensity. For further explanation, see 

 General Conclusions on p. 239. 



BoHN (1905, p. 10). After having made several observations upon 

 recently hatched larvae, he comes to the following conclusion. 

 "De ces diverses observations, il semble resulter que le sens de 

 de placement des larves de homard subit des variations occellantes 

 de signe, qui, bien que influencees par I'eclairement actuel sont 

 en relation avec les heures de la journee." 



Although certain phases of behavior in some marine animals 

 may be explainable on the ground of rhythmically recurring reac- 

 tions which bear a certain relation to the hours of the day, the 

 present writer's experience with larvae of all ages and stages of 

 the American lobster makes it quite impossible to attribute the 

 variations in the reaction of lobster larvae to such causes. The 

 hours of the day, except as they are accompanied by correspond- 

 ing diflPerences in the intensity of light, have nothing to do with 



