80 NATURAL HISTORY OF WASPS. 
hard unyielding mandibles, these may be spread out 
very satisfactorily for microscopic demonstration, 
under a glass cover with a little fluid. 
Under gentle, gradual pressure the mass divides 
into three distinct parts, one in the middle line, and 
- two others, arranged symmetrically, one on either 
side. We shall find, on a mere general.and superficial 
examination, quite enough for our present purpose, 
and indeed, our examination will be facilitated by 
mounting the object in glycerme rather than in 
Canada balsam; as the multiplicity of the details is 
not so perplexing in the less transparent medium, 
The closer we look the more there is to be seen; more 
than any books or plates will explain. 
Limiting ourselves, however, here to tracing the 
main outlines. The central piece is usually called the 
labium or lower lip, though sometimes the application 
of this term is limited to the thin membrane which 
others call the tongue or ligula. Here; applying the 
term labium to the whole central portion, we may 
adopt the term of mentum or chin for the base to 
which its several constituent parts are connected. . 
Tracing these from behind forwards, the mentum 
appears on the slide as a dark membrane lying in 
folds, shaped like a leaf. It is rounded at the pos- 
terior, but cut off square, and slightly notched, or 
stepped, on either side, at the anterior extremity. On . 
these steps the labial palpi are fitted. These are a 
pair of feelers, jointed like the antenne; only they 
are very much smaller than them in every way, and 
are clothed with fine hairs. The successive joints 
diminish regularly in length from the first to the free 
end. They are four in number; never less in any of 
