628 THE AMERICAN NATURALIST. [Vou XXXVI. 
The next stage shown is from a recently transformed adult 
(a, Fig. 16). The crinkling has disappeared, leaving the wing 
nearly flat. The processes are contracted within the cell body, 
drawing the chitinous layers close together. Near the trachez 
are shown the fully developed hair bulbs. The tracheal open- 
ings and spaces between the cells show numerous leucocytes, 
and all the hypodermis is engaged in the work of thickening 
the chitinous covering. 
In 4, Fig. 16, a section of an older wing is represented. 
The upper chitinous layer has become much thickened and the 
only traces of cells are the occasional nuclei and the thin line 

Fic. 17. — Wings of adult, x 15. a, fore wing; 4, hind wing. 
of protoplasm between the chitinous layers. In the wings of 
some insects nothing but the chitinous plates persist, but 
Sisyra seems to retain throughout this slight vestige of cellular 
tissue. 
Fig. 17 shows the venation of the fore and hind wing of Sisyra. 
It is rather simple for this family. There are few cross veins. 
The course of the principal veins may be easily followed. There 
is, however, quite an extensive variation in the tips of the main 
branches. A study of this variation should throw some light 
on the method of evolution of the peculiar hemerobian type. 
I have tabulated the extent and nature of the variation in fifty 
wings. Fig. 18 shows the type of branching of the principal 
