Hadley, Behavior of the American Lobster. 201 



called to one difference, however. It is inferred by Yerkes that 

 the sign of the phototactic response is dependent upon the pre- 

 viously assumed body-orientation of the organism. This is by no 

 means necessarily true, for in the case of the larval lobster, it is 

 clear that the orientation of the body has absolutely nothing to do 

 with the sign of the consequent progressive orientation. For our 

 present purposes we in ay, therefore, slightly modify the definition 

 of Yerkes by describing a phototactic reaction as one in which the 

 organism tends to place the longitudinal axis of the body parallel 

 to the direction! of the rays and to approach or recede from the source 

 of those rays. 



If we so limit the meaning of a phototactic response, what shall 

 we say regarding the nature of the so-called photopathic response ? 

 It is entirely possible (and indeed in the case of the larval lobsters, 

 most probable) that again the view of Yerkes (1903), that a photo- 

 pathic reaction is one in which an organism "selects" a particular 

 intensity of light, and confines its movements to the region illu- 

 minated by that intensity, is correct. But it is not so certain that the 

 photopathic responses of the lobster larvae are brought about by 

 means of slight phototactic reactions, as Yerkes (1903, p. i) sug- 

 gests for Daphnia. Therefore, for present needs, we may con- 

 clude that a photopathic reaction is one in which an organism, 

 without previous assumption of a body-orientation, "selects" regions 

 of optimal light-intensity. In the following account of experi- 

 ments and observations, we shall see to what extent the behavior 

 of the lobster larvae conforms to these definitions of phototactic 

 and photopathic reactions. 



The movements of Entomostraca toward or from a source of 

 light, and their reactions to rays of different wave lengths have 

 been made the subject of investigation by many naturalists. In 

 the earlier investigations it was commonly concluded that the 

 intensity of light was the most important factor, and that organ- 

 isms "chose" an optimal intensity. Lubbock (1881) and Gra- 

 ber (1884) found that Daphnia gather in areas of greater light 

 intensity. Schouteden (1902) found that older individuals are 

 negatively phototropic. These experiments, as repeated by Dav- 

 enport and Cannon (1897), Yerkes (1899, 1903), and Parker 

 (1902), showed that Daphnia also manifests phototactic reaction. 

 It was assumed, therefore, that some organisms may react either 

 phototactically or photopathically. Later work of American in- 



