PLECOPTERA NYMPHS OF NORTH AMERICA = 15 
pointed scissors. In the nymphs of Acroneuria, Peltoperla, ete., 
care should be taken to cut off enough of the inner portion of the 
wing pad to prevent unnecessary disturbance of the delicate 
veins or tracheae. If the mount is to be temporary only, the 
wing pads may be examined in a drop of aleohol or of water 
under the microscope, or a somewhat more permanent mount may 
be made in a glycerine jelly. For permanent mounts, however, 
it is best to stain the wing pads in a rather weak solution of 
aleohol eosin, leaving them in the stain for half an hour or 
more, and thereafter clearing the wing pads and transferring 
them to balsam. Such staining brings out the venation more 
plainly and places the preparation on permanent record. Figures 
165 to 168 show how clearly the venation may be observed in 
permanently mounted wing pads. 
The mouth parts are readily dissected out in the larger speci- 
mens, but in the smaller, more delicate species, care must be 
exercised to prevent tearing the appendages and the sclerites. 
In some eases it is advisable to carry the entire head through 
the dehydrating, clearing, and staining process, and to separate 
the mouth parts after the head has been transferred to the balsam. 
In the larger forms it will often be found advisable to soak the 
mouth parts in caustic potash for a short period. This softens 
and clears them and aids in getting rid of much of the muscle 
tissue. Appendages, such as legs, cerci, and antennae, may be 
mounted in a similar manner. In many instances, identification of 
the nymphs is possible by a careful study of the developing genital 
structures. Mature nymphs will often show these structures re- 
markably well. In some nymphs it becomes necessary, however, 
to ‘‘peel off’’ the nymphal skin before the genitalia can be dis- 
tinetly seen. This process is somewhat tedious, and is best ac- 
complished by the use of a pair of fine and very sharply pointed 
needles. Specimens which have been in alcohol for a considerable 
period of time usually respond to such treatment more readily 
than the fresh ones. After the nymphal skin has been removed, it 
is often possible to make positive identification, even though the 
genitalia may appear much distorted or flattened. 
ILLUSTRATIONS 
The drawings of the mouth parts, wing pads, and legs were 
made by means of a projecting drawing apparatus after the 
parts had been mounted on slides. The drawings of the nymphs 
were made on Ross stippling paper. The photographing of nymphs 
