THE ANATOMY OF THE STAG BEETLE. 
23 
folded transversely beneath the elytra, the fold taking place at 
the point a in the drawing of the wing (PL II. fig. 11). 
The legs exhibit the joints usually observable in insects, viz. 
the coxa, femur, tibia, and tarsus. The coxae, or basal joints of 
the legs, are sunk in suitable cavities between the plates of the 
segments to which they belong,* so as to secure freedom from 
all possibility of dislocation, with a limited motion of revolution 
in an antero-posterior direction. The motion of the femora 
upon the coxae, is in a direction at right angles to this ; as is 
also that of the tibiae upon the femora. The tarsal joints (Pl. 
II. fig. 17) are five in number, and are connected with each 
other by a ball and socket- joint, allowing of a limited motion in 
every direction. The last tarsal joint is considerably longer 
than the preceding, and is hollowed out at its extremity to re- 
ceive the enlarged bases of the terminal claws with which it is 
armed, which lie side by side within it, and are free, like the 
joints of the tarsi themselves, to move, with certain restrictions, 
in every direction. Between the claws there is a small ap- 
pendage, terminating in two minute pencils of hairs. The ex- 
quisite finish of the tarsi of this insect is well calculated to 
excite our admiration, though this may perhaps be said of every 
part of the organization of living beings in general. 
The structure of the spiracles, perhaps, more properly belongs 
to a review of the respiratory system ; a description of the ex- 
ternal structure, however, would seem to be somewhat incom- 
plete without them. They are the external orifices of the 
respiratory tubes, by means of ^ which air is conveyed to every 
portion of the body of the insect. They occur in pairs, one on 
each side of the body, from the second to the twelfth segment 
inclusive, with the exception of the metathorax, which is un- 
provided with a spiracle. There are thus ten pairs of them, 
those of the thorax being larger than those of the abdomen. 
The former can only be observed by separating the segments be- 
tween which they occur, — one pair between the pro- and mesotho- 
rax, and the other between the latter and the metathorax. They 
really belong to the posterior region of the segment in front of 
them. The abdominal series commence with a pair on the dorsal 
surface of the fifth or thoracico- abdominal segment, and are 
rendered visible by the removal of the elytra and wings. Each 
consists of a thickened oval chitinous ring (Pl. II. figs. 12, 13, 
14, and 19), within which is a more delicate, horny margin, 
fringed with branching processes (fig. 18), serving as a kind of 
sieve to exclude foreign matter. Within this, there is a valvu- 
lar aperture (figs. 12 and 13), one valve of which is provided 
with a handle-like process, into which is inserted a muscle aris- 
* The intermediate coxae are inserted between the sterna of the meso- 
and meta-thorax. 
