264 Journal of Comparative Neurology and Psychology. 



A. The Effects of Direct Lighting and Shading. Tech- 

 nique and Methods of Observation — This section deals more espe- 

 cially with the directive influence of light rays so introduced as to 

 strike the larvae from different directions; from before, from behind, 

 from the side, from above, from below, or obliquely to the body- 

 axis. These conditions were obtained, for the most part, in two 

 ways. The larvae were placed either in a cylindrical glass jar, 

 or in an especially constructed rectangular glass box (similar, per- 

 haps, to the revelateur used by Bohn), three inches wide, six 

 inches long, and tw^o and a half inches deep, all sides and the bot- 

 tom being of glass. Either of these receptacles might be placed 

 in the dark box already described. To regulate the intensity, 

 slides of colored glass were used as in the earlier experiments. 



Fig. 10. 



Fig. II. 



Fig. 10 represents a dorsal view, Fig. 11 a lateral view, of a larval lobster in the glass container. 

 For description, see Case I, p. 265. 



while to change the direction of the rays a series of mirrors was 

 employed. In certain instances, when light from the bottom was 

 required, the receptacle containing the larvae was placed upon a 

 glass plate raised a certain distance above the bottom of the box, 

 and the mirror was placed 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 diffuse daylight, and the subdued light came to the glass con- 

 tainers from several different directions. From the experiments 

 it appears very probable that in determining the orientation of the 

 organisms, the backgrounds were instrumental only in regulat- 



