850 THE AMERICAN NATURALIST. (VoL. XXXIII. 
tric arrangement of its cells. It is not at first in connection 
with nor in approximation to any trachea. The disk elongates 
and then becomes folded upon itself, thus initiating the wing 
surfaces. At the time of the folding the wing retreats from 
the surface, settling down into a pouch-like invagination of the 
hypodermis (Fig. 85, C). Thus it approaches a lateral tracheal 
trunk, from one of whose smaller branches a few small trache- 
oles now enter it. As growth continues, the wing extends 
itself slowly ventrally, as shown in Fig. 86; the mouth of its 
enveloping pouch becomes somewhat closed by the growth and 
extension of the pleural hypodermis, but to very various degrees 
Fic. 85.— Three stages in the early development of wings in Hippodamia 13-punctata: A, 
from a larva about one fifth grown; B and C, from older larvæ, less magnified; c, loose 
cuticle, shown only in B ; 4, hypodermis ; s, spine; ż, trachea; #2, tracheole ; Z, leucocyte; 
e.c., embryonic cells. 
in different specimens, a large part of the larval wing being 
often found covered exteriorly only by the chitine of the 
integument. 
During the last larval stage the wing is pushed outward and 
the fold of hypodermis overlying its edges is withdrawn radi- 
ally, and it emerges from its pouch, becoming greatly extended 
ventrally under the old larval cuticle, with its walls thrown into 
numerous folds. When the last larval skin is„shed, a still 
greater expansion transforms it into a wing of the pupa. 
Previous to their emergence from the larval wing pockets, 
there is no appreciable difference between the fore and the 
hind wings ; after this, however, the elytron shows a distinctly 
