218 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



both inavgins of both win^s, but are dili'oront upon the two inaro-ins, 

 the fore fringe being single, .shorter, and usually stouter than the hind 

 one. The veins of the fore wing alone bear more or less strongly 

 developed spines which upon the costa may even take the place of the 

 frino-e. The membranes of l)oth wings are thickly set with very 

 miiuit(% microscopic spines. In ^5Colothripida? we find wings which 

 are long, comparatively broad, and rounded at their extremities. 

 Here also the fore and hind wings are dissimilar in many respects, 

 the fore wing being stronger and far more heavily veined. The 

 fore wing has always a strongh^ developed ring vein," two longitudinal 

 veins which extend throughout the wing and unite with the ring vein 

 on each side of the tip, and four or five well-developed cross veins 

 situated as described on p. 129. The hind wings have no fully devel- 

 oped longitudinal vein and no trace of cross or ring veins. No fringe 

 is developed on the front margin of the fore wing and onl}^ a very 

 short, weak fringe is here present upon the hind wing. The veins of 

 the fore wing bear only short spines and the membranes of both Avings 

 are thickl}^ set with small spines which, though minute, are larger 

 than the similar spines in Thripida\ 



Comparing now these three types of wing point by point, and bal- 

 ancing the weight of evidence, we are led to the conclusion that Mo- 

 lothripida' and Phkeothripida stand at the extremes in respect also to 

 their wings, withThripidte somewhere between them but nearer to the 

 former than to the latter group. The strong, constantly developed 

 ring vein of ^I^volothripida^ has become much weaker or entirely dis- 

 appeared among Thripida", while in the widely divergent Phlcjeothrip- 

 idffi no trace of it is found. Cross veins are also disappearing in 

 Thripida, and their occasional presence in nuich the same position in 

 the wing as in ^^i^olothripida suggests the idea that they are under- 

 going degeneration and that this process has gone farther in some 

 species than in others. In ^Eolothripida* the longitudinal veins join 

 the ring vein near the tip, in Thripida^ they do not reach this point l)ut 

 taper out and disappear before the tip, while in Phloeothripida^ they 

 rarely reach ])eyond the middle of the wing. The micr6scopic spines 

 upon the meml)ranes and the comparative de^•elopment of the fore 

 fringes both point to this same relation of the families. In only one 

 character do the Avings of the extreme grou|)s closel}' resemble each 

 other — this is in the broadly rounded tips. The Phheothripida^ being, 

 as we have seen, the most widely divergent group, we nuist conclude 

 that, so far as wings are concerned, those of ^'Eolothripidai resemble 

 most closely the wings of Prothysanopteron. 



In regard to the ovipositor Imt little will need to be said. It is 

 always found more strongly developed in ^^^]olothripida than in Thrip- 



"ThiH lieavy riufj vein is a most remarkaV)le character and, so far as the writer can 

 learn, notliinjj: hke it is fonnd in any ntlier order of insects. 



