essive abdominal segments, as far as
the seventh or eighth, can be readily made out. The ninth and tenth
segments are at most times retracted within the eighth. The female can
protrude a long flexible tube in connexion with the eighth segment,
carrying the sclerites of the ninth at its extremity, and these
sclerites may carry short hairy processes--the stylets. This flexible
tube is the functional ovipositor, the typical insectan ovipositor with
its three pairs of processes (see HEXAPODA) being undeveloped among the
Coleoptera. In male beetles, however, the two pairs of genital processes
(paramera) belonging to the ninth abdominal segment are always present,
though sometimes reduced. Between them is situated, sometimes
asymmetrically, the prominent intromittent organ.

In the structure of the digestive system, beetles resemble most other
mandibulate insects, the food-canal consisting of gullet, crop, gizzard,
mid-gut or stomach, intestine and rectum. The stomach is beset
throughout its length with numerous small, finger-like caecal tubes. The
excretory (malpighian) tubes are few in number, either four or six. Many
beetles have, in connexion with the anus, glands which secrete a
repellent acid fluid, serving as a defence for the insect when attacked.
The "bombardier" ground beetles (fig. 5) have this habit. Oil-beetles
(figs. 23 and 24) and ladybirds (fig. 32) defend themselves by ejecting
drops of fluid from the knee-joints. The nervous system is remarkably
concentrated in some beetles, the abdominal ganglia showing a tendency
to become shifted forward and crowded together, and in certain chafers
all the thoracic and abdominal ganglia are fused into a single
nerve-centre situated in the thorax,--a degree of specialization only
matched in the insectan class among the Hemiptera and some muscid flies.

_Development._--The embryonic development (see HEXAPODA) has been
carefully studied in several genera of beetles. As regards growth
after hatching, all beetles undergo a "complete" metamorphosis, the
wing-rudiments developing beneath the cuticle throughout the larval
stages, and a resting pupal stage intervening between the last larval
instar[1] and the imago. The coleopterous pupa (figs. 2d, 3c) is
always "free," the legs, wings and other appendages not being fixed
to the body as in the pupa of a moth, and the likeness of pupa to
perfect insect is very close.

The most striking feature in the developme