66 A BOOK OF INSECTS 



wings are often much reduced and useless for flight. The 

 antenna? are long, while the last segment of the abdomen 

 usually carries a pair of jointed cerci. Metamorphosis is 

 incomplete, and the nymphal stages are passed under 

 water. When full-grown, the nymph crawls out of the 

 water, the skin splits down the back, and the winged 

 adult emerges. Stone-flies, which are dull-coloured in- 

 sects, have a world-wide distribution. About twenty- 

 four species occur in Britain, the best known being Per la 

 bicaudata, which is used by anglers as a good bait for 

 trout. 



Order V. — Isoptera. 



The " white ants," which make up this order, are more 

 correctly called termites, since they are in no way con- 

 nected with ants proper. They have biting mouth-parts, 

 while the wings, when present, are all similar in form and 

 texture, and have a transverse suture, or line of weakness, 

 at the base. Most kinds of termites dwell together in 

 social communities which comprise " kings " and " queens " 

 — i.e. males and females — and a vast company of wingless 

 forms, which are known as "soldiers" and "workers." 

 Metamorphosis is always incomplete. The Isoptera are 

 confined to the tropical and warmer regions. Two 

 families are recognised : the Termitidce, to which the fore- 

 going remarks chiefly refer, and the Embiidw. The mem- 

 bers of the latter family are very peculiar insects, about 

 whose habits very little is known, except that they have 

 no workers or soldiers. The first segment of the front 

 tarsus is provided with a gland, the secretion of which 

 solidifies into a silken thread, and is used to form tunnels 

 and galleries in which the insects live. 



