356 BULLETIN OP THE BUREAU OF FISHEMES. 



or positively phototropic. It was also noticed that these reactions were seldom negative 

 except in the fourth or later stages of the lobster. Each eye is thus apparently connected 

 with a reflex mechanism which controls the movements of a definite side of the body. 



If the light which strikes a larval lobster is suddenly blocked, Hadley found that a 

 reorientation of the body was usually effected so that the animal faced the former light 

 source. 



Generally speaking the movements of the larval lobsters seemed to Hadley to 

 support the tropism theory, and to represent simple or complex reflexes, in the 

 latter case of serial form, and resolvable, with sufficient data, into a number of simple 

 components. 



Both Bohn and Hadley have tested the effects of "screening" upon young lobsters, 

 or their behavior against white and dark backgrounds, brought to bear upon them 

 from any direction, and while the results of the observers are not wholly in accord, 

 Hadley concludes that the larvae orient themselves to the white and black screens or 

 backgrounds by essentially the identical reflex movements by which they respond to 

 direct illumination and shading. 



In the case of red monochromatic light on a white ground the lobster in the first 

 stage was found by Hadley to be negatively phototropic, but on a white ground in blue 

 light positively phototropic. In this respect, moreover, the second and third stage 

 lobsters responded in the same way, while against black the lobsters retreat from both 

 red and blue in all their stages. 



The fourth-stage lobsters, on the other hand, were observed to rise from black 

 backgrounds in light of any intensity or color; that is, to display positive phototropism, 

 and the stronger the fight, the more marked was the reaction. Against white also the 

 fourth-stage lobsters rise to any light except red, from which they tend to retreat. 



The older lobsters of the fourth stage did not respond so promptly in a positive 

 manner, and when preparing to molt they showed a negative reaction; that is, they 

 sought the bottom, a response commonly assumed in the fifth stage, whatever the char- 

 acter of the fight or background. 



The results of Hadley's experiments were in harmony with observations of the 

 behavior of the larvae confined in the 12-foot canvas rearing bags, where they showed 

 "at all times a marked tendency to sink to the bottom, except perchance at night, when 

 more active swimming is observed in all the stages. This tendency during the daytime 

 could not be controlled in any way. At night, however, it was possible to evoke a 

 seemingly positive phototactic reaction from any of the young larvae in t;he large canvas 

 bags. This was accompfished by means of the acetylene light so directed against a 

 certain area of the white field of canvas that large numbers would at once group them- 

 selves thickly about the illuminated area, manifesting in the case of the third and the 

 fourth stages, such an effort to come into the fight area that they would often throw 

 themselves out of the water, causing thereby numerous surface ripples" (131). 



