204 REPORT OF COMMISSIOXERS OF INLAND FISHERIES. 



to a great degree through the medium of the eyes and the nervous 

 systems of the larvae. But in what way this regulation is brought 

 about we are not able at the present time to state. Obviously enough 

 there here lies a problem, the solution of which would clear up many 

 perplexing questions in the field of animal behavior. 



THE MECHANICS OF BODY ORIENTATION. 



Under the present heading we shall undertake a consideration of 

 the nature of those peculiar movements which the lobster larvae 

 undergo when they are placed under diverse and changing conditions 

 of stimulation; to explain the cause of these actions, and to show 

 their relation to certain definite laws which may be said to regulate, 

 to a great degree, the body orientation of the larvse. 



The Effects of Direct Lighting and Shading. — This section 

 deals, first, with the directive influence of light rays so introduced as 

 to strike the larvse from different directions relative to the longitudi- 

 nal body axis: from before, from behind, from the side, from above, 

 from below, or at various oblique angles to the body axis, as the case 

 may be. The larvse upon which observations were to be made 

 were placed either in a cylindrical glass jar or in the rectangular 

 glass box already described. Both of these receptacles might be 

 easily placed in the dark box where the direction and the intensity 

 of the light could be regulated by mirrors and by screens. To regu- 

 late the intensity, colored slides of glass were used, while, to change 

 the direction of the rays, a series of mirrors was also employed. In 

 certain instances, when a bottom-light was required, the receptacle 

 containing the larvse was placed upon a glass plate which was raised 

 to such a distance above the bottom of the box that a mirror could 

 be introduced below. In still other instances the direction or the 

 intensity of the light was modified by the use of light-absorbing 

 (black) or light-scattering (white) backgrounds. These were used 

 more frequently when the observations were made in diffused and 

 almost homogeneous daylight, the sulxlued light coming to the glass 



