1915} Middle Membrane in Wings of Platyphylax Dit 
have nearly disappeared and are now seen restricted to a narrow 
layer along the surface of the wing just under the cuticula. It 
is seen from this section (Fig. 8) that the earlier clear layers 
now form nearly all of the wing, the long clear spaces still sep- 
arating the perpendicular strands which extend nearly to the 
cuticula. The middle membrane is much narrower than in the 
last stage but occupies the same median position and still shows 
a number of the nuclei which have wandered into it. 
During the growth of the wing in the latter part of larval life 
and while the insect 1s in a period in which the wings would be 
of about the ages found in figures six and eight the middle mem- 
brane shows, in some specimens, traces of what might be taken 
for the remains of amembrane. Running through the center of 
the middle membrane there can often be seen small dark dots 
and rods which may in some specimens be so numerous as to 
show a more or less linear arrangement (Fig. 8), this is only 
continuous for a short distance. Most of the slides examined 
did not show this central linear arrangement of dark dots and 
rods and one could see only a few darkened dots in its place; in 
most of the sections examined nothing of the kind could be 
found. We do not believe that this corresponds to a membrane 
although it occupies exactly the position in which the basement 
membrane would be found if present. 
The meaning of the wandering of some of the nuclei from 
the hypodermal layers to the middle membrane is not clear. As 
will be shown later these nuclei finally disappear and there is no 
apparent reason why they should leave those parts of the wing 
where the other nuclei are found and wander to a portion of the 
wing in which it is impossible to see that they are of any use. 
The crowding of the nuclei due to the increase in width and 
folding of the wing might necessitate a decrease in their number 
but at this stage there still remains a thin outer layer along the 
surface of the wing which is nearly free from nuclei (Fig. 6) and 
into which other nuclei might be pushed. That an accretion to 
the mass of the middle membrane is needed and supplied in this 
way is not possible as the middle membrane soon after the nuclei 
have wandered into it, begins to decrease in thickness and to 
ultimately disappear. During the stages already described 
dividing nuclei can often be seen within the hypodermal layer 
so that nuclei are both being formed in this layer and also lost to 
it from this change in their position. 
