330 Annals Entomological Society of America [Vol. XV, 



and Tenebrio, at least, it arises from the posterior tracheal trunk, as 

 in the majority of specialized insects. The corresponding vein is always 

 weak, fading out at the base, and the trachea shows a strong tendency 

 to weaken, and to lose its terminal portion to the neighboring tracheae. 

 In Tenebrio it is individually unstable, in some specimens independent, 

 in others arising from the base of Cu. In many forms its basal part 

 is a mere rudiment (labeled R in Comstock's "Wings of Insects," 

 Figs. 309, 310), while its outer part has switched its connection to 

 branches running up from Cu, or more rarely down from R. The 

 weakness of this vein and trachea would characterize it as M, even 

 were there not the further evidence of its position immediately following 

 the unmistakable Sc and R. It is a "concave" vein, like M in the 

 Lepidoptera and Neuroptera, and as in them it has no direct connection 

 to the basal sclerites. 



In all those Coleoptera whose basal venation is sufficiently spaced 

 out, there is an arculus-like bar running across from the base of radius 

 to Cu. This evidently represents an anterior arculus, being a short 

 sector of vein M (Fig. 6), whose extreme base has fused with R, while 

 it anastomoses immediately after, with Cu. In a few cases, where the 

 medial trachea is independent, it can be plainly seen, passing from the 

 radial to the medial vein-cavity through this bar. 



Cubitus. — Cubitus is a strong convex vein. Here is perhaps the 

 best opportunity for disagreement in interpretation. My identification 

 is based, first, on the position and independence of the trachea in the 

 Adephaga, which have the fullest tracheation, and in some specimens 

 at least, of various Serricorns; second, on its basal connection with the 

 axillary sclerite (though d'Orchymont considers this connection 

 secondary, a result of fusion with the vein I interpret as 1st A) ; third, 

 on the fact that the next vein (1st A) arises out of it near its base, just 

 as the vein so called does in the Lepidoptera, and several other orders, 

 and as the homologous vein (commonly called CU2) does in the 

 Neuroptera and Trichoptera. 



First anal. — The difficulty as to this vein is rather one of nomen- 

 clature than of homology, save only in the Phytophaga and Lamelli- 

 coms. In the most primitive orders there is an independent vein 

 lying between Cu and the anal fan (1st A of Comstock's figures 116 to 

 124). This is in early forms fluctuating in position, and possibly even 

 duplicated in a few cases (Comstock, Fig. 117, hind wing); attaching 

 itself either to Cu or to the anal fan; but in almost all cases lies close 

 beside the anal furrow. In the holometabolous orders it has become 

 definitely associated with the cubital stem and appears like a branch of 

 cubitus near the base. For this reason it is commonly treated as a 

 branch of Cu in certain orders (e. g., the Neuroptera) and has been 

 illogically labeled Cu2. Of course if counted at all with the cubitals 

 it would be Cus, as it would be the third branch of that stem. In 

 other orders (as the Lepidoptera and Diptera) the connection with Cu 

 is inconspicuous, either on account of a secondary splitting back, or 

 through atrophy of the vein itself (butterflies) ; and the vein has been 

 counted as independent, the true vein Cu2 being correctly so labeled. 



