No. 395.] THE WINGS OF INSECTS. 855 
In past accounts of hypodermal development in wings too 
little attention has been paid to the mechanics of the develop- 
mental process—to the varied conditions under which the cells 
labor in successive stages. To these conditions are mainly due 
the different cell forms seen ; and, except where like conditions 
are compared, different series will be contradictory. A study 
of hypodermal ontogeny in the wings of representatives of half 
a dozen orders of insects convinces us that it is impossible to 
summarize the process except in the most general terms. 
In very early stages in externally developing wings there is 
found a condition of the hypodermis not far removed from the 
normal. The cells are only a little less prismatic, a little more 
columnar or rhomboidal, and the two layers meet internally in 
very limited tracts. Fig. 89, A, is from the wing of a young 
acridid nymph. It would answer almost equally well for a 
Fic. 88. — Cross- section of et of a sna ee imago of Hippodamia 13-punctata, in 
situ: E, fore w wing; d, distal, reflexed portion of hind wing ; 
s, elytral suture ; v, a vein ; $ a cuticular thickening ; J, stridulating (?) processes; +x, the 
interlocking ridges, seen more magnified at XY. 
young nymph of the dragon-fly, Gomphus, or for several ephem- 
erids we have studied; or, for that matter, for parts of the 
ephemerid tracheal gill or for its operculum; or, save for the 
lack of trachea, for the overlapping edge of the prothorax or 
for a section of the labium. 
This early condition is followed by a long period of growth, 
during which the hypodermal cells become crowded and much 
more elongated, their nuclei, which were originally nearer their 
inner ends, coming to occupy a spindle-shaped middle portion 
in the cells (Fig. 84). The crowding is excessive, and the effect 
