Hadley, Behavior of the American Lobster. 



211 



The results of these tests and others in which the order of the 

 glass plates was changed, demonstrate the tendency of the larvae 

 to group themselves in the blue, which was the more brightly illu- 

 mined region. Similar experiments were performed with graded 

 light-screens (strips of paper of different thickness or a gelatine 

 wedge) substituted for the glass plates. The results in every case 

 indicated that here also the larvae reacted to difference in intensity. 

 These experiments were performed with a belief that it is the 

 refrangible rays of the spectrum alone that are active in deter- 

 mining the phototropic reactions of animals and plants. Min- 

 KiEWicz (1906), however, has found that, although positively 

 heliotropic animals usually react positively to the rays of shortest 

 wave-length (violet or blue), and negatively heliotropic animals 

 usually react to the rays of greatest wave-length (red or yellow), 

 these phenomena of positive phototropism and positive chromo- 

 tropism are not necessarily found together in the same organism. 

 It is uncertain whether or not the larvae of Homarus manifest chro- 

 motaxis. At the present time it can be said that the observed 

 reactions of the larvae to colored lights agree so well with the reac- 

 tions to lights of varying intensity as determined by light screens, 

 that they may fairly be considered responses to difference in 

 intensity of light. 



Experiment ^. Reaction to the directive influence of the rays — ^To 

 demonstrate the response of the larvae to the directive influence 

 of the light rays the description of a single experiment will suffice. 

 Similar experiments will be recorded later, in another connection. 

 The conditions of this experiment are like those described in 

 Experiment 2, i. e., box A was mounted over the light-shaft on 

 the colored glass plates arranged in the order blue, green, orange, 

 red. The ten first-stage larvae contained in the box were more 

 or less constantly oriented in the region of greatest light intensity, 

 that is over the blue glass. Next, the small window situated at 



