210 Annals Entomological Society of America [Vol. VIII, 
rather definite boundary with which each is surrounded; they 
persist as small, fairly regular ovoid bodies within the middle 
membrane, remaining visible until a considerably later stage, 
continually decreasing in size to finally disappear. 
Comstock and Needham (1) give a different origin for the 
nuclei in the middle membrane. They say: ‘‘In later stages, 
when, after the expansion of the wing, it (basement membrane) 
contains distinct nuclei, there is evidence that some of these at 
least are derived from the hypoderm cells whose nuclei once 
crowded up to this level, have remained stranded here after the 
expansion of the wing.’’ Later in the same work they say: 
‘““When through excessive crowding, some of the innermost 
nuclei have come into contact with the basement membrane at 
the subsequent expansion of the wing, these, seem instead to 
remain where they are, and to attract to themselves the slender 
prolongations of the neighboring cells.” 
In the stages which have already been described (Figs. 1 to 
7), the wing, except in the earliest stage, (Fig. 1), remains of 
about the same thickness and any changes taking place during 
the formation of the middle membrane and of the perpendicular 
strands go on during a partial rearrangement of the contents of 
the wing and an increase of its area. Before the larva closes its 
case preparatory to pupation the wing has grown down against 
the base of the leg and subsequent growth in a ventral direction 
is checked; covered, externally, by the cuticular layer the wing 
is confined within a limited area which it finally fills, it then 
starts to fold and this is noticed in both small and large folds 
along the surface (Fig. 8), giving it a fluted appearance, Verson 
(13). During this period and also after the larval case has been 
closed a surface view will show another system of very much 
larger folds; these start at the anterior margin of the wing and 
finally extend entirely across it, at first there are but one or two 
but an increase in their number soon occurs and gives to the 
wing a complicated folded appearance Marshall (4, Fig. 23). 
This is now that stage in the development of the wing when it 
has reached its maximum width and the perpendicular strands 
their greatest length. 
Sections through the wing at this period of its greatest 
thickness show that there has been a considerable change in its 
internal structure. The outer layers which have been very 
distinct since the beginning of the formation of the clear layers 
