a2 THE BLOWFLIES OF NortH AMERICA 
be boiled in caustic potash solutions when cleared parts are 
needed. 
If sufficient time is available larval specimens may be dropped 
alive into a warm Hetherington’s Solution which must be made 
fresh every few days. This solution is made according to the 
following formula: | 
Absolute alconel 3: > oc eeteei tact cee oe ee eee 60 ee. 
Chloroformiaee. cues ei ee ee ee 45 ee. 
Glacial’acetie acid 8. pn a ee ee 157éG; 
Pheénolé¢rystalS Su. cues os ee ee ee 30 ee. 
Specimens are left in this solution for about 24 hours, then 
transferred into a solution composed of 50 percent Hethering- 
ton’s Solution and 50 percent oil of wintergreen for an hour or 
two, and finally into oil of wintergreen for a period of 24 hours. 
This procedure gives an almost transparent larva in nearly 
natural shape, with all the sclerotized parts in their natural loca- 
tions and in nearly perfect view. 
Both the buececopharyngeal mechanism and the spiracles are 
seen to best advantage by transmitted light. Such parts may be 
dissected from the larva and placed upon a microscope slide in 
balsam. It is necessary to pass specimens preserved in 70 per- 
cent alcohol solutions through the alcohol and xylol series before 
placing them in balsam, but specimens in oil of wintergreen may 
be transferred directly to balsam. In the latter instances better 
specimens are obtained if a few drops of oil of wintergreen are 
added to the balsam. 
Detail in sclerotized areas may sometimes be studied best when 
stained. Such areas do not stain very well, but a saturated solu- 
tion of picrie acid in absolute alcohol combined with a saturated 
solution of saffranine in absolute alcohol will give satisfactory 
results in about 24 hours. Destaining may be accomplished in 
xylol if necessary. The advantage of this stain is mainly in the 
fact that it is not necessary to retrace steps from Hetherington’s 
Solution to weaker alcohols or water, then back to absolute alco- 
hol and xylol. 
EXPLANATION OF TERMS 
Only a few of the terms used in this study require explana- 
tion. Most of them have been used in the taxonomic literature of 
Dipteria or are in the taxonomic literature of other zoological 
forms, and such terms are explained in detail in most glossaries. 
Some of those employed here, however, are either new or have 
been used infrequently; these are explained below. 
