4 NEUROPTERA. 



difficulties of the study of these insects, and impeded the 

 identification of described species. Pictet first rendered the 

 essential service of pointing out the characters by which the 

 sub-imago can be distinguished from the imago ; they con- 

 sist in the dull membrane of the wings, the presence of 

 delicate fringes of hair on the margins of the wings, and the 

 distinct hairs on the caudal filaments. The form of the sub- 

 imago is analocrous to that of the imao-o, but the caudal 

 filaments and le^s are shorter. The colouring^ often differs 

 essentially ; that of the body is generally paler, with a grey- 

 ish tinge, that of the opaque wings is always darker, yellow, 

 grey or even blackish, but not bright. 



The duration of the life of an Epheviera larva will in 

 general not exceed a year; Swammerdam suspected for the 

 larva of P. longicauda a duration of several years. When 

 about to change it appears that the pupa climbs to the sur- 

 face of the water, and the sub-imago swiftly escapes from the 

 pupa skin ; it then flies to some firm object and there changes 

 in a short time (sometimes not till the following day) to the 

 imago state. The name of these creatures indicates their 

 known shortness of life, but this is only correct to a limited 

 extent. Some genera, Palingenia, Ccenis, OUooneuria, ap- 

 pear towards evening, and are gone by morning ; their life 

 is but for a few hours. The males appear before the females ; 

 copulation takes place immediately whilst on the wing (the 

 male beneath the female), and directly afterwards the eggs 

 are ejected in two clusters into the water. The emission 

 of the eggs takes place with such force that, partly through 

 the disruption of the abdomen, the two ovaries appear to be 

 ejected with their entire contents : at least in P. virgo the 

 two oval bags of eggs make this credible. The circumstance 

 that the eggs are not poured out through the oviduct in a con- 

 tinuous stream, but simultaneously in two lumps one on each 



