THE ANATOMY OF THE STAG BEETLE. 
17 
in the other orders ; and the extent of the changes which they 
undergo in order to reach maturity is in a corresponding degree 
more marked.* 
In PL II. figs. 6 and 7, will be found drawings of the Blow- 
fly and Cockroach, as illustrations of the highest and lowest types 
of insect structure. In both will be clearly seen the character- 
istics just alluded to, and in the latter especially the similarity 
of the thoracic segments to each other and to those of the abdo- 
men should be noted as evidences of a low grade of develop- 
ment. The place which the Coleoptera occupy in the scale will 
be rendered more clear when we describe the thorax, of the/ 
Stag Beetle. 
Commencing our description with the mouth-organs, we/ 
observe that the great horny mandibles, which so conspicuously 
adorn the head of the insect, are the exclusive property of the 
male sex, those of the female being small in comparison. They 
are situated immediately beneath the clypeus and labrum, to be 
presently mentioned, and are united to the upper and under 
surface of the head by a hinge-like joint, so as to work back- 
wards and forwards in a horizontal plane. They are capable of 
biting with very great force. Notwithstanding the heavy ap- 
pearance they give to the head of the insect, they are lighter 
than their bulk would indicate, being quite hollow, and" the 
cavities occupied only by a cellular mesh containing air, pro- 
bably a modification of the tracheal vessels distributed to this 
part. A strong, horny plate is seen between the mandibles on 
the upper surface, bent downwards, and constituting the labrum 
or upper lip. PI. II. fig. 1, Ir. This in most insects is articulated 
to the portion of the head immediately behind it, but in the 
Stag Beetle the two parts are immovably soldered together. 
Immediately beneath the labrum and mandibles are found the 
maxillae, or lesser jaws, PI. II. fig. 15, with which insects are 
always provided. They are partially concealed by the mentum, 
beyond which they project as two fringed lobes ; they carry a 
pair of four- jointed palpi. Their motion, like that of the man- 
dibles, is in a horizontal plane. In many beetles the office of 
the maxillae appears to be the retention of the prey within the 
mouth, and assisting the action of the mandibles. As the Stag 
Beetle, however, is a vegetable feeder, subsisting upon the 
juices of trees which it has wounded with its mandibles, these 
organs are adapted to lap up the juices thus obtained. 
Beneath these, and closing the mouth from below, are found 
the parts composing the labium, or lower lip. They consist of 
a broad, horny plate, the mentum, PI. II. fig. 2, m, immediately 
* It has been observed that as a rule the degree of perfection of an or- 
ganism or an organ is the greater the more numerous the grades of develop- 
ment are which it must traverse to attain its full perfection. 
NEW SERIES, VOL. V. NO. XVII. 
C 
