No. 373:-] THE WINGS OF INSECTS. 45 
penetrate the trachez. In this way most beautiful objects 
can be prepared, which will show the minutest ramifications of 
the trachez.! Fig. 1 is a half-tone reproduction of a photo- 
graph of an object prepared inthis way. This figure represents 
a small portion of a wing of a pupa of Corydalis cornuta. 
Not only can the trachez that precede the wing-veins be 
studied in this manner, but, if the wing be taken at the right 
stage, the cuticular thickenings destined to form the wing- 
veins, as well as their corresponding trachez, if there be any, 
can be seen. Figs. 2 and 3 are half-tone reproductions of 
photographs of wings taken at this stage. 
There is, however, one undesirable feature of preparations 
made in this manner; it is that after a time the cuticular 
thickenings become indistinct, and the glycerine jelly will 
penetrate the trachez, rendering all except the larger ones 
invisible. But as it is a very easy. matter to photograph 
such preparations, and as a series of photo-micrographs are 
much more easily compared than a series of microscopic slides, 
this feature does not materially impede an investigation of this 
kind. Usually the cuticular thickenings show best as soon as 
a mount is made, while the trachez stand out more sharply 
twenty-four hours after mounting, because of the clearing effect 
of the glycerine jelly upon the cuticular parts. It is, therefore, 
frequently desirable to make, at different times, two or more 
photographs of the same specimen. 
1 In making mounts of this kind our usual procedure was to spread a drop of 
melted glycerine jelly on a slide and allow it to cool; then to dissect off the wings 
(generally under water), taking with them just enough of the thorax to include 
the basal attachments of the trachez; then to place these wings upon the solidi- 
fied glycerine jelly on the slide; then to lower upon the wings a heated cover 
glass, causing the jelly to melt enough to envelope the wings; and then to cool 
the mount speedily on a cake of ice, a marble slab, or in a draught of cold air. 
Rapid cooling is imperative, for in melted glycerine jelly the trachez soon becom 
filled, and the smaller ones are then invisible. 
It is imperative, also, that the wings be handled with care. Being simple sac- 
like structures, the trachez are almost free within them, and a slight pinch with 
forceps in the middle of the wing may throw all of its trachez out of place. It 
is better to lift the wing by its thoracic attachments or upon a section lifter. 
Not every pupal wing is fitted for this study. Just before molting, and espe- 
cially just before the last molting, the wing becomes so crumpled within its old 
sheath that the course of its trachez can be followed only with difficulty. Much 
time can be saved by the selection of the paler individuals for study. 
