REPORT OF COMMISSIONERS OF INLAND FISHERIES. 207 



In these investigations were used screens of black and white, and of 

 such size that they coukl readily be brought close to the sides of the 

 glass containers in which the larvae were placed. Bohn has made a 

 special study of the reactions of Crustacea to the influence of such 

 screens, and in several instances the observations of the writer upon 

 the larvae of Homarus americanus are but confirmations of certain 

 phases of Bohn's work. In many cases, however, new facts have 

 been added. 



Generally speaking, it may be said that the use of the white screen 

 gave much the same sort of results as those obtained by the sudden 

 introduction of direct light; and the black screen, the same results 

 obtained by "cutting off" the light. For this reason it will not be 

 considered necessary to go into extensive details to show the nature 

 and the result of each experiment. Let it suffice to state the results 

 in a general way, and to contrast the results with those obtained in 

 the case of direct lighting and shading. 



Resume of Experiments on the Effect of Black and White Screens. — 

 When black or white screens are made to approach lobster larvae of 

 any one of the first three stages, diversely oriented, the larvae may 

 present two forms of response: First a motor reflex which tends to 

 place the longitudinal axis of the larvae in a certain relation to the 

 plane of the screen; secondly (and subsequent to the first response), 

 a progressive orientation, toward or away from the screen, as the color 

 of the screen and other conditions of the case determine. 



(1) When the white screen is employed the larvae become oriented 

 ■with, the head, in general, directed away from the screen. With the 

 use of black screens, however, the head comes to be directed toward 

 the screen, and the back more or less away from it. (2) After these 

 body orientations have taken place, the larvae may approach or 

 recede from the black or the white screen, according as they are 

 reacting positively or negatively to the directive influence of the light. 



The types of reaction upon which the body orientation- to the 

 influence of screens was found to depend, agree, for the greater part, 



