ii6 Annals Entomological Society of America [Vol.11, 



has not been so homologized without tracheal evidence that it is 

 not the second or third anal, — a statement further elucidated by 

 the appearance of a third anal trachea in many freshly emerged 

 wings. Figures i and 3 and others give the second anal trachea 

 in its characteristic position, and figures 2, 4, 6 and others give 

 a few of many mounts showing the third anal trachea also. These 

 last anal tracheae are among the first of the tracheae to become 

 invisible, so that in drawings made with other points in view, 

 they are frequently not indicated, as they had cleared before the 

 other points at issue had been finished. 



The presence of the second and third anal tracheae in the nym- 

 phal wing pad has not been established in those species of aphids 

 in which the nymphs were studied. What the history of these 

 tracheae is, then, previous to their appearance in the recently 

 emerged wing is not yet ascertained. 



THE HIND WING OF APHIDID^. 



The hind wing of Chaitophorus populicola (fig. 7) will serve as 

 an illustration of the tracheation of the hind wings of the more 

 generalized genera. In figure 9 of the Macrosiphum pisi the four 

 tracheae -are distinct to very near the base of the wing. Usually 

 a greater degree of coalescence has taken place even for this 

 species. 



By referring this wing to the front wing of Chermes (Plate XIX) 

 we can readily homologize the unbranched radial trachea, the 

 simple medial trachea, the cubital trachea and the^ first anal. 

 Like the second anal of the fore wing, the first anal of the hind 

 wing appears only as a trachea and is not followed by a vein. 



The same tracheas occur in the other more generalized genera, 

 and also in Pemphigus (fig. 13) where the front wing is specialized 

 by the reduction of veins in media. When we reach Chermes 

 (fig. 30), however, we find, in spite of the wealth of secondary 

 tracheae, only the radial and medial tracheae marking the courses 

 of succeeding veins and these are coalesced at the base. 



The venation of the hind wing is, then, homologized, as follows : 

 the marginal costa and the very faint subcosta, both of which, 

 due to the lack of mechanical necessity found in the front wing, are 

 not well developed; the radius represented by the radial sector 

 only; the media always simple; and in the more generalized 

 genera, cubitus. The venation of Tetraneura (fig. 17) is of 

 interest. The front wing has the venation of Pemphigus and 



