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PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXVI. 



attached to the cubital trunk at the place where the anal vein bends 

 strono-ly awa}' from it. In all the Zygoptera I have been able to 

 examine, all the ])ranchcs of the anal vein have been transferred to 

 the cubitus in both wings, the anal trunk lieing very greatly reduced 

 or wanting (see Plate XXXI, fig. 2). 



Such transference of the branches of the anal trachea lends the 

 strongest support to the assumption alread}- made regarding the trans- 

 ference of the trachea Es to the media, in which case possible reasonsi 

 for shifting and reattachment were much more clear. 



The cDial loop. — Owing to such shif tings of trachea, owing also to the 

 expansion of this region in some wings, occasioning the development 

 of accessory tracheal branches and its reduction in others, causing alli 

 the branches to disappear, the homologies of those branches which arei 

 oftenest present are followed with difficulty. Two of them, however 

 (designated as A^ and A.^ in the figures), must be considered here, since 

 they together form an inclosure, which ])ecomes one of the strongest; 



Fu;. 17.— FOKMS OF the anal loop in the ANISOPTERA: 1, ANAL LOOP OF Cyclophylla diphylla 

 2, OF Gomphokles stujinatus; 3, of Gomphxschna furc'llata; 4, of Gornpliomacromia imradoxa; 5, oi 

 Syncordulia gracilis: 6, of Agrionoptera insignis; 7, of (?) Nannophya maculosa; 8, of Ephidatii' 

 longipcs; 9, of Hydrobasileus extraneus. 



of the supporting structures of the expanded anal area of the hinc 

 wings of the Anisoptera. This inclosure may fitly be designated a.'- 

 the anal loop (al. of all the figures). Fig. 17 will serve to show some 

 of its more common and characteristic forms. 



In some Aeschnine genera we find a supplemental loop (al') devel 

 oped between veins A^ and Chi^^. Fig. 3 of Plate XXXI shows how 

 this is brought about; it is another accompaniment of the widening ol 

 the base of the wing. Since in the Libellulidaj the anal loop extends 

 from vein A^ to vein Ou^a., it is to be considered as the equivalent o: 

 both loops in Anax. Of the characteristic foot-shaped loop of th( 

 commonest Libelkdidte the "toe" is of later development, and result 

 from the concurrent elongation of veins A.^ and C>/^^ with the expan 

 sion of the hind angle of the wing. 



After considering these changes severally, if we again compare for( 

 and hind wing in an}- of the more specialized Libellulidse we shall sec 



