no 



A. S. PEARSE. 



The light reactions of the commensals were tested. Animals 

 were placed in a flat dish containing sea water. This dish was 

 barely enclosed by a box two feet long and sixteen inches wide. 

 The box was painted black on the inside and light was admitted 

 through an aperture two inches high across the lower side of one 

 end. When a Pinnixa or a Polyonyx was placed in the box 

 before a window it usually went toward the light and tried to get 

 through the glass for a time. It soon began to wander about 

 the dish, however, and after twenty-four hours spent most of 

 the time in the darkest end of the box. When ten individuals 

 of the same species were put in the dish simultaneously their 

 behavior was essentially the same. Twenty Pinnixa and seven 

 Polyonyx were left together in the box several days. When the 

 lamp was lighted before the opening of the box at night most of 

 the crustaceans went toward it and tried to get through the 

 end of the glass dish, but after an hour they became scattered 

 about the dish without particular reference to the light. Mast 



FIG. 6. Pinnixa undergoing ecdysis. The left-hand figure shows a ventral, 



the right-hand a dorsal view. 



('ii, p. 284) mentions several animals which, though usually 

 negatively phototropic, may become positive for a time after 

 mechanical or other stimulation. Apparently steady light is 

 not, as a rule, an important factor in the daily life of Pinnixa and 

 Polyonyx, but if confined under unnatural conditions they may 

 go toward a light. Such reactions might enable them to escape 

 from confinement. Both Pinnixa and Polyonyx responded 

 readily to a decrease in light intensity. The former was very 

 active when placed in a glass dish and kept its legs continually 

 in motion ; but if an object was passed between it and the window 

 it became motionless at once. Though Polyonyx was more 



