No. 395.] THE WINGS OF INSECTS. 847 
In the Plecoptera, Ephemerida, Hemiptera, Blattidz, e¢ al., 
the external changes during growth are comparatively slight— 
increase in size and internal differentiation, and the develop- 
ment of the veins and of the basal articulations. In the more 
specialized Orthoptera there occurs the well-known reversal of 
position of. the wings at the last molt. In the Odonata there 
are the noteworthy differences that the wings arise in an erect 
position upon the body wall, and at midway the length of their 
respective segments, and not from the hind margin (Fig. 82, D). 
They appear at a time when the tergum and the pleura are very 
Fic. 83. — Dorsal part of at tion of a nymph of ee elisa, one third grown : 
d, dorsum; ø, pleu ; d.v., dorsal vessel; ż, 7, tracheæ ; #2, m, muscles in cross-section ; 
med, muscles in longitudinal section ; 7. Juv 2, developing muscle of ka wi ming; a. hind 
wing ; fw, fore wing; a and d 
C, costa; Sc, subcosta ; pm the coalesced radius and media ; Cz, cubitus; A, anal vein. 
little chitinized, and are hardly more identified with one than 
with the other. Later, as in the saltatorial Orthoptera, owing 
to a rapid growth of the pleura, especially at the wing bases, 
they are pushed over upon the dorsum and lie in an inverted 
position (Fig. 82, Æ, F), to be righted only at the final trans- 
formation. 
Fig. 83 shows the relations of parts in a dragon-fly nymph 
one third grown. It represents a partial cross-section passing 
through the posterior part of the basal attachments of the hind 
wings and through the fore wings just before the arculus. In 
the hind wings are seen (a, J) the cut ends of the transverse 
