THE ANATOMY OF THE STAG BEETLE. 
19 
of integument immediately surrounding this orifice is termed 
the occiput. 
The complexity of structure in the head of the insect renders 
it futile to attempt to discriminate certainly the several seg- 
ments of which, it is composed from a study of its own structure ; 
the only light that can be thrown upon it must be derived from 
an examination of the insect while yet in the egg. It is other- 
wise, however, with the succeeding portion of the body, the 
thorax, where, as has been already stated, the segmental division 
is much more apparent than in the Metabola of Packard, but 
the regional distinction less so. Hence results the possibility of 
mistaking at a first glance the large square piece which follows 
the head for the equivalent of the whole of the thorax, as we see 
it in the Bee or the Fly, the truth being that this is only the 
first of the three rings of which the thorax is composed, namely, 
the prothorax, as is immediately evident by the consideration 
that it carries only the anterior legs. Hence, also, arises the 
more intimate union and continuity of the metathorax with the 
abdominal segments, of which we shall have occasion to speak. 
The thorax is usually said to consist of three segments of the 
insect, viz. the second, third, and fourth segments, reckoning 
the head as one ; but this is not strictly accurate, as the fifth 
segment, in a partially atrophied condition, is very frequently, 
as here, intimately united with it, and in the Hymenoptera is 
included in front of the thoracico-*abdominal incisure, as we 
shall presently explain. Here, also, is seen the most typical 
form of the insect segment, equally removed from the simplicity 
of the abdominal and the high complexity of the cephalic rings. 
Each consists primarily of four pieces — a dorsal, a ventral, and 
two lateral plates, as seen in the ideal section, PI. II. fig. 9. The 
ventral plate is frequently called the sternum. Between the 
dorsal and lateral plates are placed the insertions of the wings, 
and those of the legs are found between the lateral and ventral 
plates. It is, however, by no means easy to follow out this 
ideal. The dorsal plate of the prothorax is very marked, being 
the large square plate between the head and the elytra (Pl. II. 
fig. 1 , pr) ; the ventral plate is also clearly marked, see PI. II. 
fig. 2, st ; it is the large piece extending in front of and between 
the coxse (ex). The lateral plates of this segment are not easy 
to trace. The French naturalist, Audouin, distinguished two 
parts in them, and illustrated them by dissections of the Great 
Water Beetle, Dylicus circumflexus. They are an anterior por- 
tion, the episternum, and a posterior portion, the epimeron. 
The former portion it is difficult to recognise at all in the Stag 
Beetle ; and the latter is the narrow piece, which, in PI. II. 
fig. 2, epim , is seen extending behind the coxa. On careful 
* See note to p. 21. 
