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THE AMERICAN NATURALIST [Vol. XL VIII 



At the first tap, the larva, which had been crawling 

 toward the window, immediately turned away from the 

 light. Before it resumed its positive response to the light, 

 the paper was tapped again; the negative response con- 

 tinued. In this way the larva could be kept crawling away 

 from the light indefinitely. Disturbance makes the reac- 

 tion of the larva to light temporarily negative; otherwise 

 it is positive. 



SUMMARY OF ExPEEIMENTS 



Euthrips tritici, when disturbed, is positively photo- 

 tropic in both larval and adult stages. It is positively 

 stereotropic, and the stereotropism is stronger than pho- 

 totropism, at least under certain circumstances. Some 

 individuals appear to be on the whole positively geo- 

 tropic ; others are indifferent. 



Anaphothrips striatus. — Adult males are usually nega- 

 tively phototropic. Females taken from exposed situa- 

 tions are usually indifferent to light, those from concealed 

 situations usually negative. The larvae are usually in- 

 different to light, regardless of the kind of place from 

 which they are taken ; a single larva that was positive was 

 made negative by keeping it in the dark. Adults are posi- 

 tively stereotropic. The females and larvae are positively 

 geotropic. 



Anthothrips verbasci. — Adults taken from concealed 

 situations are usually negatively phototropic, those from 

 exposed places tend to be indifferent to light. The larvae 

 are all negatively phototropic, except the full-grown ones, 

 which may be indifferent. The larvae are plainly posi- 

 tively stereotropic, the adults less plainly so, or not at all. 

 Neither adult nor larva responds to gravity. 



Interpretation of the Experiments in their Relation 

 to Distribution and Behavior of Thrips in Nature 

 With the evidence from these experiments before us, 

 may we not interpret the observed distribution and be- 

 havior of the Thysanoptera in nature somewhat as fol- 

 lows? Instead of explaining the fact that Euthrips tritici 



