214 Annals Entomological Society of America [Vol. VIII, 
The wing, as this last folding continues, decreases more and 
more in thickness (Fig. 13) but structurally there is no notice- 
able change. Here and there places are seen in the sections 
where the hypodermis and middle membrane have increased in 
thickness (Fig. 14) but such places are apt to be near the margin 
of the wing. The cause of this is not known unless it can be 
due to the folding of the wing which may push the hypodermis 
and the middle membrane in such a way as to increase, at 
certain places, the thickness of each. 
After the folding of the wing has reached its maximum 
(Fig. 15) certain changes have taken place. Most noticeable of 
these is the final disappearance of the middle membrane and of 
the small degenerated nuclei which it contained. After this has 
occurred the perpendicular strands again pass entirely across 
the wing and directly connect the two hypodermal layers with 
each other. These layers are now thinner and their nuclei are 
so arranged that the longitudinal axis of each lies parallel to 
the surface of the wing. 
No marked change is noticeable in the wing after the adult 
insect has emerged (Figs. 16 and 17). The wing has become a 
little thinner and the hypodermal layers show a decrease in 
amount and their nuclei are smaller. The activities of the dif- 
ferent layers have ended and there is little left within the wing 
of what was present during the early stages of its development 
and growth. 
From the foregoing account it can be seen that in Platyphylax 
the term middle membrane cannot be used to designate a true 
membrane but rather as the name for the thin layer of proto- 
plasm occupying a median position within the wing. As has 
been noted by others this layer is not continuous during the 
entire development and growth of the wing but disappears and 
is reformed in the same place. Of these two structures the 
latter is the more membrane like. 
In the preparation of the material two or three of the com- 
moner sublimate, acetic acid fixitives were used and the slides 
stained with Delafield’s hamatoxylin or with alum carmine. 
