VII THRIPS 531 



and is found in concurrence with diversity as to winged and wing- 

 less females of the same species, so as to have given rise to the idea 

 that the phenomena in this respect are parallel with those that 

 are more widely known as occurring in Aphidae. Under certain 

 circumstances few or no males are produced (one of the cir- 

 cumstances, according to Jordan, being season of the year), and 

 the females continue the species parthenogenetically. In other 

 cases, though males are produced tliey are in very small numbers. 

 Some species of Thysanoptera are never winged ; in others the 

 individuals are winged or wino-less according to sex. But there 

 are other cases in which the female is usually wingless, and 

 is exceptionally winged. The winged specimens in this case 

 are, it is thought, of special use in disseminating the species. 

 Jordan has suggested that these phenomena may be of a 

 regular nature, but Uzel does not take this view. Another 

 condition may be mentioned, in which the species is usually wing- 

 less, but winged individuals of the male as well as of the female 

 sex occasionally appear. Thrips lini apparently makes regular 

 migrations, feeding at one time underground on the roots 

 of flax, and then changing to a life in the open air on other 

 plants. 



' Numerous forms of Thysanoptera, belonging to both of the 

 great divisions of the Order, have Ijeen found fossil in Europe 

 and North America, but all are confined to deposits of the Tertiary 

 epoch. 



Of the 135 species known to Uzel, 117 are European ; they 

 are divided into two Sub-Orders. 1, Terebrantia, in which the 

 females are provided with an external toothed ovipositor, of two 

 valves ; 2, Tubulifera, in which there is no ovipositor, and the 

 extremity of the body is tubular in both sexes. The British 

 species are about 50 in number, and were described by 

 Haliday about 60 years ago ; ^ of late they have been very 

 little studied. 



The name Physopoda or Physapoda is used for this Order, 

 instead of Thysanoptera, by several naturalists. 



^ Eiitomolorjical Magazine, iii. 1836, p. -139, and iv. 1837, p. 1-44. 



