ut having the opposing inner
edges furnished with interlocking serrations. The whole of this
apparatus is commonly termed the mask. In a state of repose it is
applied closely against the face, the elongated mentum directed backward
and lying between the anterior pair of legs; but when an approaching
victim is seen the whole apparatus is suddenly projected, and the prey
caught by the raptorial palpi; in some large species it is capable of
being projected fully half an inch in front of the head. The prey, once
caught and held by this apparatus, is devoured in the usual manner.
There are two pairs of thoracic spiracles, through which the nymph
breathes during its later life by thrusting the anterior end of the body
into the air; but respiration is mostly effected by a peculiar apparatus
at the tail end, and there are two different methods. In the
_Agrionidae_ there are three elongate flattened plates, or false gills,
full of tracheal ramifications, which extract the air from the water,
and convey it to the internal tracheae (in _Calopteryx_ these plates are
excessively long, nearly equalling the abdomen), the plates also serving
as means of locomotion. But in the other groups these external false
gills are absent, and in their place are five valves, which by their
sudden opening and closing force in the water to the rectum, the walls
of which are furnished with branchial lamellae. The alternate opening
and closing of these valves enables the creature to make quick jerks or
rushes (incorrectly termed "leaps") through the water,[1] and, in
conjunction with its mouth parts, to make sudden attacks upon prey from
a considerable distance. Well-developed Aeschnid larvae have been
observed to take atmospheric air into the rectum. The lateral angles of
the terminal abdominal segments are sometimes produced into long curved
spines. In colour these larvae are generally muddy, and they frequently
have a coating of muddy particles, and hence are less likely to be
observed by their victims. If among insects the perfect dragon-fly may be
termed the tyrant of the air, so may its larva be styled that of the
water. Aquatic insects and larvae form the principal food, but there can
be no doubt that worms, the fry of fish, and even younger larvae of
their own species, form part of the bill of fare. The "nymph" when
arrived at its full growth sallies forth from the water, and often
crawls a considerable distance (frequently many feet up the trunk