158 Annals Entomological Society of America [Vol. VIII, 
visible, when they do first appear the wings have started to 
decrease in thickness. As already mentioned there is a stage in 
the development of the wing at which all cells of the hypo- 
dermis are similar and occupy an even layer just under the 
cuticula (Fig. 3); then some of these cells adjacent to the 
developing veins and at the margin of the wing increase in size 
and move away from the surface. With the exception of the 
trichogens at the two last mentioned places there is an even 
layer of hypodermal cells, all similar and equidistant from the 
cuticula, covering the areas between the veins and it is from some 
of these that the surface hairs develop. 
Here and there in this even layer of hypodermis certain of 
the nuclei increase in size and move inward and away from the 
cuticula; these are similar to the enlarged nuclei which form the 
trichogens of the vein and marginal hairs except that the nuclei 
are different in their position on the wing and have no relation 
to the veins or margin. This is the first indication of the 
trichogens of the large surface hairs and when one (Fig. 10) is 
compared with the trichogen of a vein hair (Fig. 5) their sim- 
ilarity is apparent. Strands are seen coming from the free 
margin of the former and appearing very similar to part of the 
wall of a developing vein; they are, however, only some of the 
protoplasmic strands which extend from the hypodermis to the 
middle membrane (‘‘Grundmembran”’). 
As in the trichogens of the vein hairs the cytoplasm of these 
cells is often darker colored than that of adjacent cells and can 
be seen as dark streaks through the hypodermis (Fig.11). From 
a surface view (Fig. 12) this same darker cytoplasm may be seen 
surrounding the nucleus of each trichogen but it is not notice- 
able in the other hypodermal cells. The same increase in sur- 
face of the nucleole that was noticed in the vein trichogens is 
seen, but to a less extent, in these nuclei (Fig. 13) and, when 
the secretion of the hair becomes active, several nucleoles are 
noticeable in each trichogen nucleus. 
Small surface hairs. These hairs are so numerous upon both 
surfaces of the wing that there are very few hypodermal cells, 
excepting those taking part in the formation of the other kinds 
of hairs, from which one is not formed. In looking at the surface 
of a wing in which these small hairs have been developed one can 
examine many cells without finding one from which a small sur- 
