156 Annals Entomological Society of America [Vol. VIII, 
under the cuticula, cell boundaries are very hard to differentiate 
but the elongated, irregular, ovoid nuclei are fairly regular in 
their arrangement (Fig. 3). From the inner surface of the 
hypodermis come off a number of strands of protoplasm many of 
which, at this stage of the wing’s development, pass across from 
surface to surface and connect the two layers of hypodermis with 
each other; these strands have nothing to do with the develop- 
ment of the wing hairs. The first indication of the trichogens, 
cells from which the hairs develop, is noticed in that certain of 
the nuclei of the hypodermis increase in size and then, with 
some of the surrounding protoplasm, push in from their original 
position towards the median part of the wing and away from the 
cuticula. These trichogens which first appear are situated 
adjacent to a vein and between it and the cuticula (Fig. 4). 
Nearly all of these trichogens lie along one side of the section; 
this is the upper surface of the wing upon which surface most of 
the hairs develop. The trichogen nuclei differ in position and 
size from the normal ones of the hypodermis, they also become 
more circular in outline but do not as yet differ in structure. At 
the same time that the trichogen nuclei wander away from the 
surface of the wing it is noticed that other nuclei go with them, 
these latter retain their normal size; they can be found in 
younger stages of the trichogen’s growth (Figs. 5, 6, 7) and also 
after the hair has been developed (Fig. 8). What function these 
nuclei may perform is not known. This differs a little from the 
account of Mayer (6) who found that in Lepidoptera the 
trichogens first grow outward, towards the cuticula, while in 
Platyphylax we find that the movement is at first opposite to 
this and that the trichogens wander inward, away from the 
cuticula. 
In the regular hypodermal cells each nucleus has one, some- 
times two, rather small nucleoles which did not stain with 
hematoxylin or alum carmine. The trichogen nucleole, also 
non-staining, is at first similar to that of the other nuclei but 
enlarges with the growth of the nucleus until it becomes very 
noticeable (Fig. 6). At a later stage cell boundaries are more 
easily seen and the trichogens differentiate themselves from the 
other cells not only in this respect but also by the darker 
appearance of the cytoplasm; this fact, that the trichogens 
stain more deeply than the regular hypodermal cells was 
