ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 253 



The interstitial species are further divided into anthophilous forms 

 (flower-dwellers) and phlceophilous forms (under bark scales on trees). 



Experiments on Eitihrips tritici show that it is positively phototropie 

 when disturbed, in both larval and adult stages. It is positively 

 stereotypic, and the stereotropism is stronger than phototropism, at 

 least under certain circumstances. Some individuals appear to be on 

 the whole positively geotropic ; others are indifferent. 



Experiments with Anaphothrips striates show that adult males are 

 usually negatively phototropie. Eemales taken from exposed situations 

 are usually indifferent to light, those from concealed situations are 

 usually negative. The larvae are usually indifferent to light, regardless 

 of the kind of place from which they were taken. A single larva that 

 was positive was made negative by keeping it in the dark. Adults are 

 positively stereotropic. The females and larvae are positively geotropic. 



Experiments on Anthothrips verbasci show that adults taken from 

 concealed situations are usually negatively phototropie ; those from 

 exposed places tend to be indifferent to light. The larvae are all 

 negatively phototropie, except the full-grown ones, which may be 

 indifferent. The larvae are plainly positively stereotropic, the adults 

 less plainly so, or not at all. Neither adult nor larva responds to gravity. 



Shull's conclusion is that the outdoor behaviour and distribution of 

 the Thysanoptera are in large measure the result of responses to simple 

 stimuli, and do not imply any degree of choice. The responses are 

 often adaptive, but they are probably not purposeful. How they have 

 arisen is unknown. Natural selection may be responsible for the pre- 

 servation of the useful, and it may have eliminated responses' that were 

 harmful. But other responses of no value whatever, though quite 

 harmless, may have been allowed to persist, without help or hindrance 

 from selection. 



Thrips as Pollinator of Beet-flowers. — H. B. Shaw* has found 

 that beets, supposed to be self -fertilized, are in every generation cross- 

 fertilized, and that an important agent in the process is a minute un- 

 conspicuous Thrips insect, so small that it readily passes " through the 

 meshes of fine silk chiffon." Perhaps other Thrips insects may be a 

 cause of unsuspected cross-pollination and unaccountable " mutation " 

 in the breeding of cereals and other plants. W. E. Castle f calls attention 

 to the great importance of this to students of genetics. 



Mouth-parts of Anoplura.J — Bruce F. Cummings describes the 

 mouth-parts in Polyplax {P. oxyr/iynchus), which include two chitinous 

 structures lying together behind the pharynx, which are quite probably 

 mandibles, and thus traces of the mandibulate ancestry of Anoplura. 

 In another species, P. brachyrhynchus, there is an oesophageal sclerite 

 just behind the mouth-opening. This sclerite (sometimes called lyriform 

 organ, and homologized with the hypopharynx) is associated with 

 " glands" (better called basal pieces). They are almost unique in the 



* Bull. U.S. Dept. Agric, No. 104 (July 1914). 



t Amer. Nat., xlix. (1915) pp. 121-2. 



% Ami. Nat. Hist., xv. (1915) pp. 256-9(2 figs.). 



June KJtlt, 1915 T 



