52 Papers from the Marine Biological Laboratory at Tortugas. 



They were allowed to remain active for lo minutes and were then placed in 

 bright light, where they again stopped all movement in less than 30 seconds. 

 They were observed closely for 10 minutes while in the light, and not a 

 leg or antenna was moved, though some had stopped in apparently awk- 

 ward positions. 



The foregoing experiment was repeated several times on different in- 

 dividuals and at various periods during the day, always giving similar 

 results. Aplopus is thus seen to become active in the dark within from 10 

 to 20 minutes, and at times even more promptly. This activity is continued 

 as long as it remains in the dark. When the insect is placed in bright light 

 it promptlv comes to rest within from less than 30 seconds in some cases to 

 several minutes in others. Aplopus responds, therefore, more promptly to 

 liglit than to darkness. The males appear to come to rest more readily than 

 the females ; they are also more active in the dark. These insects may 

 readilv be made to mate by placing a number of individuals of both se.xes in 

 a cage in the dark. 



The question next arises whether responses to light and darkness are due 

 to the action of the stimulus on the optic organs or to the effects of light 

 on the body-surface of the insect as a whole. In attempting an answer to this 

 question several experiments were performed. First, a number of Aplopi 

 were chosen and their eyes were well covered with a lampblack paste until 

 they were apparently blind. These individuals were then subjected to dark- 

 room experiments. When only the compound eyes were blackened, the 

 simple eves being uncovered, they still responded in the dark-room, though 

 slower than the control. On one occasion a male and three females were 

 used; the male moved slightly after 15 minutes, though almost an hour had 

 elapsed before all four individuals had become active. 



When both the simple and compound eyes were blackened they responded 

 still more slowly in the dark. Of four treated in this manner only one 

 had moved after 30 minutes in the dark-room, and this one almost imme- 

 diately came to rest again ; so that after 50 minutes all were quiet, three of 

 the four not having moved during this time. After 2 hours three were at 

 rest and one was moving ; one of the four had not moved at all during the 

 two hours and the three that had moved did so only for a moment, not 

 becoming really active, as they normally do in the dark-room. 



To test further the importance of vision in responding to changes from 

 light to dark, I determined to blacken the compound and simple eyes of a 

 number of Aplopi during the night to ascertain in what manner they would 

 respond when the daylight appeared. Six females and two males were 

 placed in a cage to themselves and their eyes were painted at 9'' 40™ p. m., 

 while they were all very active. At 5'' 30"" a. m. on the following morning 

 three of the females and one of the males were actively moving. These 

 animals were much more active than the control of about 50 individuals, all 



