Hadley, Behavior of the American Lobster. 217 



individuals taken from these groups, whose age was accurately 

 known. During the course of the study, the history and the daily 

 reactions of three groups of larvae were followed and recorded. 

 For the following account of the reactions of the first-stage larvae, 

 for instance, the records of these three groups for the first day, the 

 second day, the third day, etc., were used. Only the reactions 

 which appeared to be the most constant and typical have been 

 introduced here. Therefore, although many variations in reac- 

 tions were found to occur, the following section describes the 

 typical daily reactions of the larval lobsters from the time of hatch- 

 ing through the fifth stage of their existence. 



I. First Larval Stage. 



As has been shown by preliminary observations and the 

 experiments already mentioned, the lobsters of the first larval 

 stage are usually strongly positive both in their photopathic and 

 in their phototactic reactions. These reactions are manifested 

 strongly in the few hours directly after hatching, when, as we shall 

 presently see, the young lobsters react definitely, and to very 

 slight differences in the intensity of illumination. When half- 

 hour old lobsters were placed in the glass jar, and submitted to 

 any kind or intensity of light (daylight, artificial, or colored), they 

 responded well (especially when the intensity was increased by a 

 white background) to slight difi^erences in illumination; and reacted 

 uniformly and invariably by moving, tail foremost, toward the 

 source of light. In case of two sources of light, on opposite sides 

 of the jar, the larvae would respond to the rays which were the 

 more intense. If the rays from two sources of light were intro- 

 duced at right angles to each other, the resultant reaction, as has 

 been shown for other organisms by many investigators, was deter- 

 mined according to the law of the parallelogram of forces. 



It would appear that, in the behavior of the first-stage larvae, we 

 have the most delicate reactions to slight differences in light inten- 

 sity that occur throughout the life of the lobster. During the 

 early hours of the first larval stage, no individuals reacted nega- 

 tively to the directive stimulus of the light, while in the later stages, 

 although a majority of the larvae manifested definitely one reac- 

 tion or another, there were usually a few individuals which gave 

 responses that were either indefinite or opposite to the rule. 



