206 Annals Entomological Society of America [Vol. VIII, 
posed of a single row of cells with ovoid nuclei which are 
arranged in two or three apparent rows. The long narrow cells 
are so crowded together that the nuclei have lost their regular 
linear arrangement and have been pushed towards one end in 
the cell to which they belong. The nuclei are situated more in 
the basal half of each layer so that there is a thicker portion of 
protoplasm along the free surface of the hypodermis than 
between the nuclei and the basement membrane. In the spec- 
imens of Platyphylax examined the cell boundaries, which have 
been figured by other observers in different insects, could not be 
found with any great regularity and only here and there could 
traces of any boundaries separating the cells be seen. The 
hypodermis covering the thorax and that forming the peripodial 
membrane has a distinct basement membrane, this can also be 
seen on that part of the hypodermal layer forming the wing 
rudiment although in this last place it is not distinct (Fig.1,B.m). 
The two layers of the wing rudiment, as its development pro- 
ceeds, approach each other and pass through a stage in which 
there is but a narrow open space separating them from each 
other; here and there this open space is wider forming large 
openings, the developing wing veins. Narrow open spaces are 
also noticed between the cells of each layer, these do not as yet 
entirely separate the cells but appear only in the basal region; 
this is, however, the beginning of that separation of the cells 
which finally results, with the migration of the nucleus and 
protoplasm to one end, in the formation of the elongated, spin- 
dle-like cells which have been described in the developing wings 
of a number of insects. An endeavor to find a basement mem- 
brane in the wing rudiment shows that it is not distinct and 
continuous, it can sometimes be seen but cannot be traced for 
any considerable distance along the basal surface of either 
layer. Other workers have observed the basement membrane 
at this stage in different insects although, as quoted in the 
introductory remarks, all have not seen it with equal distinctness. 
- As the development of the wing goes on its two layers finally 
approach each other and their inner surfaces touch except where ‘ 
the developing wing veins are present. The two basement 
membranes should now lie adjacent to each other and fuse to 
form the middle membrane. An examination of sections at this 
stage shows however, that a continuous median membrane 
separating the two layers of the wing from each other cannot 
