No. 421.] SKELETON OF THE HEAD OF INSECTS. 27 
of the coxa. In front of the coxa there is a triangular /7o- 
chantin (tr), with its apex pointing towards the middle line of 
the body. Between the trochantin and the ventral arm of the 
episternum there are two sclerites, — one next the trochantin, 
the antecoxal piece ; and one next the episternum, not yet named, 
which may be termed the second antecoxa! piece. The antecoxal 
piece at its mesal extremity ( y)articulates with 
the coxa. This articulation may be termed 
the ventral articulation of the coxa. 

THE SCLERITES OF THE HEAD AND NECK. 
The segments of the body of an insect 
do not fall into three well-marked groups, — 
head, thorax, and abdomen, — as commonly pi 
defined in the text-books. Between the head Fis. :7.— The base of a 
and the thorax there is a more or less distinct — 4^ ^ "ere 
neck, which in some insects contains several sclerites. As we 
believe that these cervical sclerites form a part of the second 
maxillary or labial segment, it is necessary to include them in 
a discussion of the sclerites of the head. We shall return to 
them later. 
If an embryo insect be examined after the appearance of 
the mouth and the appendages, the cephalic end of the body 
will be found to consist of a central swelling, the procephalon 
(Fig. 7, fr), and a large lobe on each side, the cephalic lobes 
(Fig. Joel). 
The procephalon has been commonly described as the rudi- 
ment of the clypeus and thelabrum. This is doubtless correct 
if the term c/ypeus be taken in the broader sense by which it 
includes the clypeus anterior and the clypeus posterior of 
Newport; and this is evidently the sense in which it has 
been used by nearly all writers on the embryology of insects. 
Hence, according to the nomenclature adopted in this paper, . 
the procephalon is the rudiment of the front, clypeus, and 
labrum. he 
This conclusion makes evident the significance of the epi- 
cranial suture. The sclerites lying in front of the arms of © 

es 



