Hadley, Behavior of the America}i Lobster. 



209 



It will be seen that the larvae "seek" the light area. Next the 

 paper was so arranged that the shaded part was below, as shown 

 in Fig. 3. In this case the larvae were always found uniformly 

 in the unshaded area. In all cases the body-orientation of the 

 larvae was determined by the direction of the rays of light, which 

 struck the tube at right angles; but at no time, it would seem, 

 could this directive influence alone have been instrumental in 

 causing the larvae to remain in the region of greater light-intensity. 

 The same general results were obtained when the tubes were laid 

 horizontally on the table (Fig. 4) but still at right angles to the 

 direction of the incident light rays which came from the side. 

 These tests of the reaction of larvae in glass tubes appeared at 

 first sight to demonstrate that larvae of a certain age and stage 

 show a tendency to group themselves in regions of greater illumi- 

 nation, irrespective of the directive influence of light or of reaction 

 to gravity. This, however, is not the only possible conclusion 

 to be drawn from these facts. 



To take, for instance, the case of the horizontally lying tube 

 (Fig. 4), in which the larvae gathered in the illuminated ends (the 

 region of greatest light-intensity), and there oriented to the direc- 

 tive influence of the light. In the darkened area of the tube the 

 larvae did not undergo body-orientation, but swam about in many 

 directions. When occasionally, they entered the more brightly 

 illuminated end of the tube, they at once oriented to the directive 

 influence of the rays and took the position shown in Fig. 4. 

 Furthermore, the larvae usually manifested a tendency to retain 

 their body-orientation and thus to remain in the illuminated region 

 when once they had entered it. Here, then, we have a case where 

 the apparent reaction to the intensity of light is, in reality, deter- 

 mined, and maintained, partly at least, by the orienting response 

 to the directive, influence of light. In other words, the larvae did 



