Hadley, Behavior of the Atjiericaii Lobster. 253 



in the area farthest from the light, eighteen allowed themselves to 

 be stranded rather than to retrace their course into deeper water, 

 and in so doing to approach the light. ^ 



Case 2. Fifth-stage lobsters — When the same experiment in- 

 volved the fifth-stage lobsters, the results were similar. The only 

 difference that could be observed was that the intensity of the 

 reaction was greater for the fifth-stage than for the fourth. The 

 result of twelve tests, each with ten lobsters showed the distribu- 

 tion to be as follows: Area i, nine; 'area 2, ten; area 3, twenty- 

 one; area 4, eighty, of which seventy were "stranded." These 

 last would have perished, had they not been returned to the water 

 at the end of each successive test. 



(C.) Conclusions concerning the reactions to light of fifth-stage 

 lobsters — The results of the foregoing experiments on the reactions 

 of fifth-stage lobsters, demonstrate the following points: (i) Like 

 the fourth-stage lobsters, the fifth-stage lobsters are negatively pho- 

 totactic from the beginning of the stage to the end of it, and this 

 holds good for all intensities of light which cause any reaction 

 whatever. (2) Unlike the early fourth-stage but much like the 

 late fourth-stage lobsters, the fifth-stage lobsters are negatively 

 photopathic from the beginning of the stage to the end. (3) This 

 negative photopathic reaction, unlike the photopathic reactions 

 of the earlier stages (in which case the photopathic reaction was 

 entirely subservient to the phototactic), has itself become a well 

 grounded tendency, and, although it can be modified, it can not be 

 entirely obliterated (so far as its value in causing a certain orienta- 

 tion is concerned) by the tendency to react to the directive influence 

 of the light rays. (4) The intensity and energy with which the 

 late fourth-stage, but especially the fifth-stage, lobsters manifest 

 a negative phototactic reaction may lead to results fatal to the 

 lobsters themselves. 



{D.) Contact-irritability versus reaction to light — In the preced- 

 ing section the phototactic and the photopathic reactions, together 

 with some points of their inter-relation, have been considered. 

 We shall now examine that response of lobsters to solid portions 

 of their immediate physical environment which may be ascribed 

 to contact-irritability or thigmotaxis. 



It frequently happens that single types of reaction (phototaxis, 

 chemotaxis, geotaxis, and the like) may be studied to best advan- 



* It should be noted, however, that the water in no case receded more than 5 to 10 mm. as measured 

 horizontally on the bottom of the box. 



