50 Papers from the Marine Biological Laboratory at Tortugas. 



grasping her abdomen about its middle, his third pair of legs usually hang- 

 ing freely extended, the tip of his abdomen being firmly attached to a 

 slight pit on the ventral surface of the seventh abdominal segment of 

 the female. The intromissive organ of the male is then protruded and 

 placed between the oviscapt and the last three abdominal segments of the 

 female. In this position the male remains for from 30 minutes to several 

 hours. His copulating organ is then withdrawn, although he may still re- 

 main for a long time sitting upon the back of the female (fig. 4, plate 3). 

 One male may copulate with several females during the same day. The 

 male often gives periodical quivering movements while over the female, prob- 

 ably for the purpose of exciting her to the sexual act. He sometimes shows 

 a slow, swinging motion during copulation. 



The female is supplied with a long ovipositor, although it seems to be 

 useless, as her eggs are allowed to fall carelessly to the ground as she sits 

 motionless among the branches. The eggs resemble closely in size and color 

 the seed of Suriana, as mentioned before, but diflfer from them considerably 

 in shape. (Compare figs. 4a and 4b in plate i.) 



All of the observations on the habits of Aplopus in nature would seem 

 to indicate that the behavior of this insect is as truly protective as is its close 

 simulation of the branches on which it lives. 



EXPERIMENTAL. 



EXPERIMENTS WITH LIGHT. 



Aplopus responds to light and darkness in a most interesting manner. 

 The insects were observed to begin moving on the bushes by a much brighter 

 light in the evening than that which served to stop their movement during 

 the morning. They were seen feeding and crawling slowly about, at times, 

 two hours before sunset ; while they often came to rest more than half an 

 hour before sunrise. The difference in intensities of the lights causing the 

 two reactions is very great. It occurred to me that perhaps their response 

 was periodic and not entirely due to the effect of light; that is, after being 

 active for several hours during the night they become tired and cease to 

 move for this reason, and not on account of any response to light, since the 

 intensity of the morning light by which they come to rest is even less than 

 that of the moonlight in which they are active. (The quality of the two 

 lights is no doubt different.) The case is, however, made clear by the fol- 

 lowing experiment : 



Sixty-five individuals in a wire cage had come to rest at 4'' 50™ a. m. 

 At this time daylight was scarcely perceptible. It was much darker than 

 when they had begun movement during the evening, or even the moonlight 

 of the earlier part of the night. It would seem, then, that a physiological 

 periodicity had had some influence on their behavior. To test this the cage 

 was placed in a dark-room at 5 a. m. In less than half an hour all were 



