FLAT-WINGED GROUP 3137 



terminal joints, and the labial palpi three jointed. The thorax is square or oblong, 

 with its three segments almost equally developed. The tarsi are three jointed, and 

 have their claws separated by a bilobed pad. The species of this family are not 

 numerous, though some are almost world wide in their distribution. The adults 

 appear about the same time as dragon flies and alder flies, and frequent nearly the 

 same places. Though they have large enough wings, they fly heavily, and not for 

 any considerable distance at a stretch, and are generally most active in the evening. 

 The female fastens her eggs loosely together, and drops them in masses as she flies 

 over water. The larvae are mostly found in rapid streams, where they keep under 

 stones, or among broken pieces of wood, and live by preying actively upon the 

 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 larvae, or nymph, leaves the water by climb- 

 ing 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 the opposite page. 



The termites or white ants ( Termitidce} differ considerably in one 

 Wh't A t res P ect fr m a ll the other groups of Pseud oneuroptera. They live in 

 societies which are of a highly organized 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 maxillae with five-jointed 

 palpi, and a lower lip (labium), divided at the end into four lobes, and bearing 

 three-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; the}' are long, narrow, not very closely veined, each wing 

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