202 The Orders of Insects 



of the water. This family is distributed in all parts of the world 

 except the farthest northern regions (127)- 



Agrionidae. — The Agrionida are dragonflies of more slender build, 

 though some exotic genera (^Megatoprepus and Mecistogaster for 

 example) have longer abdomens and a wider wing-spread than any 

 other insects. The head is relatively very wide, so that the two 

 eyes are always far apart. The wings of the two pairs are exactly 

 alike, and there are nevermore than two ante-nodal cross nervules. 

 The larvae are provided with three tracheal gills at the tail-end of the 

 body, rarely also with paired gills on the abdominal segments ; rectal 

 gills are sometimes present in a rudimentary condition, and the older 

 nymphs breathe, like those of the Libellulidje, through thoracic 

 spiracles. The family has as wide a range as the Libellulidse (127). 



ORDER 10.— NEUROPTERA. 



In this order are included a number of families 

 whose members agree in the possession of biting jaws 

 and (with few exceptions) four nearly similar wings 

 with complex net-veining. They differ markedly in 

 their life-histories from those insects already described 

 which resemble them superficially, as they all undergo 

 a complete metamorphosis ; the larva is usually eruci- 

 form. As characters drawn from the life-history are 

 not available when adult insects only are before the 

 student, it may be well to point out the cardinal 

 structural distinctions between the order Neuroptera 

 as here restricted and the preceding groups formerly 

 included in it. The Plectoptera (Mayflies) and 

 Odonata (Dragonflies) are both too distinct to be 

 confused with any other insects ; their reduced feelers 

 distinguish them, at a glance, from the present Order. 

 Among the Platyptera, the Perlaria have folding hind- 

 wings which are unknown among the true Neuroptera, 

 while the winged Corrodentia are distinguished by their 

 simple neuration, and incompletely fused second maxillae. 



An adult insect then may be recognised as belong- 

 ing to the present order, by the possession of con- 

 spicuous feelers and four membranous wings with 



