206 REPORT OF COMMISSIONERS OF INLAND FISHERIES, 



or forward, in which the body of the larva forms a constant part 

 of the circumference of the circle of rotation. 



2. Revolutions on the Longitudinal Axis of the Body or '' RoUi7igs." — 

 The revolutions or rollings may take place either to the right or left^ 

 but usually in such direction that the back of the larva becomes 

 directed more or less toward the light. They may be through a few 

 degrees or they may exceed 90 degrees, in which case the larva falls 

 to the bottom. In the case of larvse which have suffered injury to 

 one eye, these revolutions may take place very rapidly — often at the 

 rate of one hundred and fifty per minute— and always in a deter- 

 mined direction. 



3. Swingings of the Longitudinal Axis of the Body. — These are in 

 such direction that the head is brought to face the dark, and the tail 

 to point toward the light. The swing is always of such a nature 

 that the head is brought, by the shortest path, to face the dark. 



4. Rotations in the Radii of a Circle. — In these the longitudinal axis 

 of the larva forms a radius and, with either the head or the tail at 

 the center, the larva rotates about a fixed point. This type of reac- 

 tion is uncommon and, as yet, unexplainable. 



These four types of movement seldom occur separately, except 

 under especially devised experiment. Two or more of these types 

 usually are found blended to form composite types of action. To 

 these previously mentioned simple componets, all the movements of 

 the larval lobsters may be reduced. 



The Effects of Screens and Backgrounds.— GeneraWy speak- 

 ing, it is fairly probable that the reactions to light, which are brought 

 about through the use of backgrounds, are dependent upon the same 

 factors and conditions of illumination which may be produced by the 

 employment of light-absorbing or light-scattering screens. For this 

 reason we mjght consider the effects of screens and backgrounds 

 together, were it not for the fact that the nature of the experiments 

 makes it more advantageous to treat the two subjects separately: 

 first, the effect of screening upon the body orientation of the larvse. 



