172 
INSECTS. 
weaker creatures inhabiting the same waters. They have strongly developed jaws, 
and rather long palpi. They breathe by means of tracheal gills, in the form of 
tufts of filaments, attached to the bases of the legs and the sides of the integument 
which joins the three thoracic and the first abdominal rings to one another. The 
two filamentous tails may have a pair of tracheal tufts at their base. In later 
stages of their life the larvae exhibit rudiments of wings. When the time for its 
transformation arrives, the full-grown larva, or nymph, leaves the water by 
climbing the stem of a plant, or crawling some distance up the bank until it finds 
a dry stone on which to stand, when the emergence of the imago takes place in the 
usual way, preceded first by a splitting of the larval skin along the middle of the 
thorax. When the insect is free, its wings dry rapidly, and it is soon ready to fly. 
A fact of importance, first noticed in the Perlidce, though it also occurs in 
some other groups, is that the tracheal gills are retained by the perfect insects, 
where they are attached in the same places as in the larva, but much reduced in 
size, and probably, in most cases, functionless. As an example of the Perlidce, one 
of the best known British species, Perla bicaudata, is figured on p. 171. 
Termites, or The termites, or white ants ( Permitidce ), differ considerably in 
White Ants. one respect from all the other groups of Pseudoneuroptera. They 
live in societies which are of a highly organised and complex nature and most 
resemble those met with among insects of the highest type, such as bees and ants. 
This is, however, the only direction in which the termites diverge to any extent 
from the rest of the Orthoptera; for, like all these, they pass from the larval to 
the adult state by a series of gradual changes; while, in the structure of their 
bodies, they show an affinity with some of the lowest groups of the order. In the 
termites the head is free and distinct, with the antennas composed of a number of 
small bead-like joints, and rather short. The perfect insects have compound eyes, 
and, as a rule, two ocelli; but the wingless individuals are generally without eyes 
of any kind. The mouth-parts, which are constructed on a clearly orthopterous 
plan, are not very unlike those of a cockroach, and consist of a distinct upper lip 
(labrum), two strong horny mandibles, a pair of two - lobed maxillse with five- 
jointed palpi, and a lower lip (labium), divided at the end into four lobes, and 
bearing tliree-jointed palpi. In the thorax the first segment is well developed, and 
its dorsal plate, or pronotum, is rather broad and flat; the other two segments being 
less strongly developed, though in the winged insects attaining a fair size. Both 
pairs of wings are much alike; they are long, narrow, not very closely veined, each 
wing being marked by a transverse suture at a short distance from the base; and in 
a state of rest they are laid flat over the back. The legs are slender, and well fitted 
for running, and their tarsi are four-jointed. The abdomen has a slightly elongated 
or oval form, and carries two very short appendages—the cerci—near its extremity. 
The common habitation of a society of white ants is known as a nest; and in 
each nest, which is divided into a number of cells or chambers communicating with 
one another, there may be found several different kinds of individuals in addition 
to the larvae. Some are provided with wings, or with the rudiments thereof, and 
are distinguished also by having eyes. These are the sexually developed males 
and females, which are capable of reproducing their kind; though this function is, 
as a rule, carried on by a single couple in each nest. The king and queen—as this 
