216 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



tant structures which we must uotice are the antennae, wings, and ovi- 

 positor. What are the chief points of difl'erence that we find in the 

 structure of these organs'^ Only a modification in the structure of 

 each organ has taken place. In ^Eolothripidte we find always nine 

 segmented antemuB, comparatively broad wings, which are rounded at 

 their extremities, and have, in the fore wing, the fore fringe and 

 the spines along its veins very weakly developed, a strong ring vein, 

 two longitudinal veins, and four or five cross veins, and finally a 

 strongly developed ovipositor, which curves upward toward the tip of 

 the abdomen. In Thripida? we find antennae with from six to eight 

 segments, wings which are nearly always slender and quite sharply 

 pointed at their tips; that in the fore wing the fore fringe and numer- 

 ous spines along its veins are nearly always well developed, two 

 (sometimes only one) longitudinal veins are present, the ring vein is 

 rarely strongly developed, cross veins are absent or but slight traces 

 of them occasionally appear, the ovipositor is moderately well devel- 

 oped in most cases, but sometimes is small, weak, and functionless, 

 though it is always plainly present and curves downward away from 

 the tip of the abdomen. 



Between these two families we shall find it much more difficult to 

 decide just what influences may have favored the development of the 

 differences noted. Certainly many influences were concerned, and 

 they could not have been of such a nature as to favor such radical 

 changes as have resulted in the development of the Tubulifera. Rather 

 than attempt to outline these varied influences and their prolxible 

 results, we prefer, in this case, to base our conclusions upon the gen- 

 eral tendencies which now appear to be acting, and which we may 

 reasonably assume to have been acting in the same way during much, 

 perhaps all, of the past history of this suborder. 



We have shown that Phloeothripidse have diverged more widely from 

 Prothysanopteron than have any other members of the order. A 

 comparison of the antennte in the three families will aid us in deter- 

 mining the order in which the families must be arranged. In the 

 Phloeothripidifi these organs are always eight segmented. The inter- 

 mediate segments are, as a rule, much thicker in the middle than at 

 the ends, and are sometimes rounded. Stout spines are borne around 

 the apical thirds of segments two to six, inclusive, and more slender 

 spines are more generally distributed over the last two segments. A 

 whorl of small spines stands also around the first third of each segment 

 from three to six, inclusiv^e, and simple, stout, specialized sense cones 

 are borne at about the outer third of these segments in most cases. 

 The antenna} of Thripidse consist of from six to eight segments, of 

 which the intermediate ones are always considerably thicker in the 

 middle than at their ends. Stout spines are usually present around 

 the apical ends of segments two to five inclusive. More slender spines 



