No. 421.] SKELETON OF THE HEAD OF INSECTS. I5 
Although the clypeus almost always appears to be a single 
sclerite, except when divided transversely as indicated below, 
it really consists of a transverse row of three sclerites, — one 
on the median line and one on each side articulating with the 
mandible. The median sclerite may be designated the clypeus 
proper, and each lateral sclerite, the antecoral piece of the man- 
dible. Usually there are no indications of the sutures sepa- 
rating the clypeus proper from the antecoxal pieces; but in 
some insects they are distinct. In the larva of Corydalis 
the antecoxal pieces are not only distinct 
but are quite large (Fig. 3, ac, ac). TT 
In some insects the clypeus is com- 
pletely or partly divided by a transverse | 
suture into two parts (Fig. 1). These 
may be designated as the first clypeus 
and the second clypeus, respectively ; the 
first clypeus being the part next the front 
(Fig. 1, Cr) and the second clypeus being l 
that next the labrum (Fig. 1, C2). ic 
There is a great lack of uniformity in L 
the application of the term cZyfeus, aris- es Ha dde ra 
ing from the fact that many writers apply 
it to the entire area between the epicranial suture and the 
labrum; either overlooking the fact that the part here 
designated as the front is a distinct sclerite, or, following 
Newport, terming it the cZypeus posterior. But as the front 
and the clypeus (in the more restricted sense) pertain to 
different segments of the head, it is desirable to use dis- 
tinct names for them; and as the names proposed by New. 
port are morphologically incorrect, the so-called clypeus 
posterior being in front of the so-called clypeus anterior, as 
will be shown later, it is doubtless better to use the older 
term frons, or front, for the sclerite next the epicranial 
suture, and to restrict the term clypeus to the part termed 
clypeus anterior by Newport. 
The Labrum (labrum, Vlliger). — A movable flap which con- 
stitutes the upper lip of the mouth (Fig. 1, Z). The labrum. 
is the last of the series of unpaired sclerites between the 





