104 PROCEEDINGS OF THE NA TIONAL MUSEUM. vol. xxvi. 



/Spines upon tvings. — In the Terebrantia the entire upper surface of 

 the wing is thickly set with microscopic spines which are wanting in 

 Tubulifera. Besides these there are usually borne along the longitu- 

 dinal and costal veins some larger, prominent spines, which vary in 

 number, size, and arrangement sufficiently to give in many species of 

 the Thripid{i3 characters of specific and generic value. Those borne 

 upon the costa appear intermixed with the fringe hairs, though reall}^ 

 they are not in the same plane. Their development seems to be in 

 inverse proportion to that of the fringe, so that when the latter is 

 strongly developed the costal spines are not larger than those upon 

 the other veins, but when the fringe is weak or absent the costal 

 spines develop greatly and to some extent replace it. 



In ^Eolothripida? the spines upon the veins are always quite small, 

 while the front fringe of the fore wing is wanting. In Phloeothripidje 

 there are usually three stout, erect spines near the base of the vein in 

 the fore wing. 



Taking flight. — It has been frequently noticed and mentioned that 

 manj^ of these insects throw up the end of the abdomen, much as do 

 the rove beetles (Staphylinida?), as though threatening to sting. This 

 movement is made to assist in the proper spreading of the wings for 

 flight. When at rest, the fringe hairs lie along the hind edges of the 

 wings and are more or less interlaced. As the abdomen is raised, the 

 wings are drawn down over its sides in such a manner as to make it 

 appear that the spines upon the sides of the abdominal segments are 

 used to some extent as a comb by means of which the hairs are 

 straightened out and put in their proper position. This operation 

 often has to be repeated several times before the wings are brought 

 into a condition for successful flight. The power of springing, pos- 

 sessed by some species, also seems to be of assistance in taking flight. 

 These statements appl}" only to Terebrantia, however, no observations 

 having been made upon Tubulifera. 



Coordination of the wings. — This is accomplished in a manner 

 strongly suggestive of the Hymenoptera, though the structures con- 

 cerned are less highly developed. Upon the costa of the hind wing, 

 near its base, stand about five short spines in Terebrantia and two or 

 three in Tubulifera, which are hooked at their tips. When the wings 

 are spread in flight these tiny hooks engage a membranous fold on^ 

 the underside of the scale of the fore wing. Beyond these small ^ 

 hooks stands a single stouter spine which also forms a hook. Froi 

 the hind angle of the scale of the fore wing proceed two long, stoul 

 spines, standing so closely together as to often appear like one, anc 

 these engage the solitarj^ stouter hook on the hind wing. Thus unitec 

 the wings move together, but as the connection is so near the bases oi 

 the wings it can not be very strong. 



Reduction oftJie wings. — It is an interesting fact that in this ordei 



