202 Annals Entomological Society of America [Vol. VIII, 
on other parts of the body and, 1n the very young wing bud, the 
continuation of the one into that of the other can be easily seen. 
The young wing is formed by a fold of the hypodermis which at 
first remains unchanged and the two walls of the fold come to 
lie adjacent to each other, they finally come together and the two 
opposed basement membranes fuse to form the middle mem- 
brane. This happens early in the development of the wing 
and has been seen, clearly by some observers, indistinctly by 
others. Later in the development when the hypodermal cells 
have assumed their characteristic spindle shape this middle 
membrane persisting, or a new one forming, has been clearly 
seen as a well marked layer passing through the median portion 
of the wing and connected at either side to the hypodermal cells 
by long strands. This is the layer first described by Semper (10) 
and Schaffer (9) and it has been seen by nearly all those who 
have studied the development of an insect’s wing by means of 
sections. 
It might be well to give a few views of those who have 
studied the development of the wings of insects although not 
trying to make such a series of quotations complete. Comstock 
and Needham (1) working with beetles say: ‘‘It is also impor- 
tant to note that the basement membrane of the hypodermis of 
the wing differs in no respect from that of the hypodermis of the 
body wall, and is continuous with it. In the thinner parts of 
the wing the two basement membranes melt and fuse, this 
forming what has been termed the middle membrane of the 
wing.” 
Mercer (6) in speaking of the Lepidoptera says: ‘‘In sec- 
tions of the wing buds made at this time (fifth larval stage) the 
so-called middle membrane is seen only with difficulty. This 
has given rise to the belief that it disappears at this time. Later 
when the wings become more opaque, i. e., in the pupa stage, 
the two basement membranes are again easily seen.’’ Again 
the same author says: “Students of the subject have been 
confused by descriptions of three different structures, the base- 
ment membrane of the hypodermis, the middle membrane of 
the larval wing buds, and the ‘Grundmembran’ of the pupal 
wing; when in reality there is only a single structure, the 
basement membrane.”’ 
Mayer (5), who worked with Lepidoptera, says: ‘‘The 
middle membrane has disappeared as such, and in its place one 
