580 THE AMERICAN NATURALIST. [VoL. XXXIII. 
costo-radial and the cubito-anal groups respectively.! To the 
former belong the costa, the subcosta, and the radius; to 
the latter, the cubitus and the anal veins. These groups find 
their attachment to the main tracheal system of the body at 
points wide apart ; in the Perlid genus, Capnia, the former group 
springs from the dorsal lateral trunk, the latter from ventral lat- 
eral trunk of the thorax.? Even in such groups as Trichoptera, 
Hymenoptera, and Diptera, where great reduction has taken 
place, the persisting tracheæ clearly represent these two groups. 
The media is sometimes a member of the costo-radial group 
(Fig. 80) and sometimes of the cubito-anal group (Fig. 76). In 
Sc 
Fic. 80. — Fore wing of a nymph of a cockroach. 
certain forms, however, the media arises midway between these 
two groups from a transverse basal trachea which joins them, 
suggesting at once the possibility of its migration from one 
group to the other. Since there is no evidence of its having 
entered the wing independently, to which of the two groups did 
it belong in the primitive winged insect? The answer lies (1) 
in the rank of the insects showing the different conditions, and 
(2) in the ontogeny of the media itself. 
(1) Only in the Plecoptera and in some of the Blattidæ does 
the media clearly belong to the costo-radial group, and in these 
there is no basal transverse trachea connecting the two groups ; 
1 American Naturalist, vol. xxxii, p. 88. 
2 A fact of no little interest in its relation to the question of a former respira- 
tory function in these or closely related parts; since tracheal gills are commonly 
joined to both longitudinal lateral trunks, securing, doubtless, better distribution 
of the air. 
