STONE-FLIES, MAY-FLIES, DRAGON-FLIES, ETC. 257 



are of the biting kind, but are weak, sometimes even 

 membranous. The coxse are small, and wide apart. 



The eggs are extremely numerous and are shed in water. 

 The larva (Fig. ii6) much resembles the adult, except for 

 the absence of wings and for the presence, in many cases, 

 of three pairs of filamentous gill-tufts, one tuft behind the 

 base of each leg. The larvae are usually found in rapid- 

 flowing water, under stones, and they are carnivorous ; from 

 their usual situation they are not to be regarded as at all 

 common enemies of mosquito-larva;, though the question 

 whether they may be inimical to Simulium larvae, which also 

 live in coursing water, deserves attention. In an aquarium — 

 where of course the larva of Simulium is rather impotent — 

 Perlid larvae certainly feed on Simulium larvae. 



Order Ephemerida : May -flies. 

 (Gr. e^)5/xe/30? = living but a day.) 



This order contains a single family, the Ephemeridce — 

 delicate insects that in the adult winged phase exist but 

 a few hours, a day or two at the utmost ; but which have, as 

 aquatic larvae, a life of considerable duration. 



The adult Ephemerid has filmy net-veined wings, of 

 which the hind pair are very much smaller than the front 

 pair, or may even be absent. The eyes are large, especially 

 in the male, in which sex, in some species, each eye may be 

 divided into two distinct organs. The antennae are short, 

 and are composed of i or 2 stoutish segments and a slender 

 style. The mouth-parts are vestigial and functionless, since 

 the transient existence is devoted entirely to reproduction, 

 and no food is taken ; but the digestive tube is present and, 

 being filled with air, acts as a balloon. The mesothorax, as 

 in other insects of sustained flight, is the chief component of 

 the thorax. The front pair of legs are particularly long, 

 especially in the male. The abdomen consists of lo seg- 

 ments, and ends in two or three extremely long filamentous 

 cerci, which at sight distinguishes these insects from midges. 

 The adult Ephemerid shortly after it has flitted from its 

 pupal tube casts its skin, even the skin covering the wings, 



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