No. 567] BIOLOGY OF THE THY SAN OPT EE A 167 



was turned toward a small window, while the room was 

 rather dimly lighted. All the thrips crawled rapidly 

 toward the window. When the position of the tube was 

 reversed, the thrips reversed their crawiing, again going 

 toward the window. The reaction was definite and in- 

 variable. 



Exp. 3. — A close-fitting sleeve of black building paper 

 was slipped over one half of the glass tube used in experi- 

 ment 1. The thrips were collected at the exposed end by 

 turning that end for a few minutes toward the window. 

 The covered end of the tube was then turned toward the 

 window. The thrips crawled rapidly toward the light, 

 until they reached the shadow of the sleeve. Here they 

 crawled about, apparently aimlessly, for half an hour an 

 inch or two within the sleeve or just outside it. 



Contact. Exp. 1. — When, in the light experiments, the 

 tube was reversed in position as soon as the thrips 

 reached one end, the insects immediately turned toward 

 the opposite end. But if the tube was allowed to rest for 

 some time, the thrips became settled quietly between the 

 glass and the sloping surface of the cork. The tube could 

 then be carefully reversed, and most of the thrips re- 

 mained lodged between cork and glass for many minutes, 

 some of them for hours. The positive reaction to contact 

 counteracted the positive reaction to light. 



Exp. 25. — A larva of this species was placed on a glass 

 plate, upon which rested a microscope slide. When the 

 larva in its crawling reached the slide, it came to rest in 

 the angle formed by the glass plate and the edge of the 

 slide. It remained there many minutes until disturbed. 



Gravity. Exp. 17. — An adult female was placed in a 

 glass tube which was enclosed in a black sleeve to exclude 

 light, and the tube placed in a vertical position. The posi- 

 tion of the thrips was marked with a wax pencil before 

 putting on the sleeve. The sleeve was then removed mo- 

 mentarily at frequent intervals, and the position and 

 direction of crawling of the insect noted. Most fre- 

 quently it was found lower than the previous position, 



