No. 567] BIOLOGY OF THE THYSANOPTERA 169 



negative to light was placed on a sheet of blotting paper. 

 A small square of glass was placed over her, and sup- 

 ported at one edge, so that in crawling away from the 

 window the thrips approached the edge of the glass which 

 was in contact with the paper. She soon became lightly 

 wedged between the glass and the blotter, and came to 

 rest. Blotter, thrips and glass were then carefully 

 turned through 180 degrees so that the negative reaction 

 to light would have led the thrips out of its crevice ; but 

 she remained there for a long time. Positive reaction to 

 contact overcame the negative reaction to light. 



Another female, indifferent to light, was placed under 

 a similar glass. In her random crawling she became 

 wedged between the blotter and glass, and, notwithstand- 

 ing that the blotter was occasionally turned in the mean 

 time, remained there several hours, until I lifted the glass. 



Another female, not negative to light, was placed under 

 a similar glass square. She crawled from under it, but 

 happened to crawl against the edge of the microscope 

 slide that supported the glass cover. She settled quickly 

 into the right angle formed by the slide and the blotter, 

 and remained there a long time. 



Gravity. Exp. 21. — A female which was indifferent to 

 light was placed in a glass tube, and the tube set in a 

 vertical position. The thrips immediately began to crawl 

 downward. The tube was reversed, and the thrips im- 

 mediately reversed its direction. A sleeve was placed 

 over the tube to exclude the light, and frequently removed 

 temporarily to observe the position of the thrips. In 

 every case she was found crawling downward. 



When the tube was held in an oblique position, the re- 

 sult was the same ; the thrips crawled down the slope. If 

 she was already crawling down, a slope of 5 to 10 degrees 

 was found to be sufficient to keep her going in the same 

 direction. But to reverse the direction of crawling, it 

 was necessary to create a slope of about 45 degrees in the 

 opposite direction. The same positive geotropism was 

 shown when the thrips was placed on an inclined sheet of 



