Plectoptera 199 



wherein the larval and nymphal stages are passed. 

 The grubs are very unlike their parents being typical 

 campodeiform larvae perfectly adapted for an aquatic 

 life. In the younger stages, breathing takes place 

 through the skin, but about the third moult (in Cloeon 

 at least) paired abdominal gills and tracheal tubes are 

 developed. The long tail-processes of the larva also 

 serve as breathing organs, blood being driven back- 

 wards into them by a special hind chamber of the 

 heart. The grubs feed on vegetable matter and small 

 aquatic animals. After a long larval life, with many 

 moults, the nymphal stage with rudimentary wings 

 is reached, though the form of the nymph differs 

 markedly from that of the imago. The winged form 

 which emerges from the last nymphal instar is not the 

 mature Mayfly but a "sub-imago"; this, by a final 

 moult, gives rise to the true imago. Such a moult in 

 the winged state is not known to occur in any other 

 group of insects (3, 126, lyo)- 



The Plectoptera include only a single family — the 

 EpketneridcE containing about 300 known species and 

 distributed in all parts of the world (125). 



ORDER 9.— ODONATA. 



Structure. — The Dragonflies which. make up this 

 order are easily recognised by several well-marked 

 characters. The head is large and very freely movable 

 on the prothorax ; the compound eyes are large and 

 semi-globular, and there are three ocelli. The feelers 

 are short, with two stout basal, and four or five 

 slender segments, forming a bristle-like termination. 

 The mandibles are powerful; the first maxilla has the 

 hood and blade fused together, forming a spiny jaw- 

 plate, and its palp has but one segment. The palps 

 of the second maxilla have very broad and flat sub- 



