40 THE DURATION OF LIFE. 



towards the middle and end of September they are much less 

 plentiful than the females. 



Acridium migratorium 'dies after the eggs are laid' (Oken, 

 ' Naturgeschichte '). 



The male Termes probably live for a short time only, although 

 exact observations upon the point are wanting. The females ' seem 

 sometimes to live four or five years,' as I gather from a letter from 

 Dr. Hagen, of Cambridge, Mass., U.S.A. 



JSpkemeridae. Rosel, speaking of Ephemera vulgata (' Insekten- 

 belustigungen,' Bd. II. der Wasserinsekten, 2 te Klasse, p. 60 et seq.), 

 says: 'Their flight commences at sunset, and comes to an end before 

 midnight, when the dew begins to fall.' ' The pairing generally 

 takes place at night and lasts but a short time. As soon as the in- 

 sects have shed their last skin, in the afternoon or evening, they fly 

 about in thousands, and pair almost immediately ; but by the next 

 day they are all dead. They continue to emerge for many days, so 

 that when yesterday's swarm is dead, to-day a new swarm is seen 

 emerging from the water towards the evening.' ' They not only drop 

 their eggs in the water, but wherever they may happen to be, on 

 trees, bushes, or the earth. Birds, trout and other fish lie in wait 

 for them.' 



Dr. Hagen writes to me ' It is only in certain species that 

 life is so short. The female Palingenia does not live long enough 

 to complete the last moult of the sub-imago. I believe that a 

 female imago has never been seen. The male imago, often half in its 

 sub-imago skin, fertilizes the female sub-imago and immediately 

 the contents of both ovaries are extruded, and the insect dies. It 

 is quite possible that the eggs pass out by rupturing the abdominal 

 segments.' 



Libellula. All dragon-flies live in the imago condition for some 

 weeks ; at first they are not capable of reproduction, but after a few 

 days they pair. 



Lepisma saccfiarina. An individual lived for two years in a pill- 

 box, without any food except perhaps a little Lycopodium dust 1 . 



,' 

 II. NEUROPTLKA. 



Phryganids ' live in the imago stage for at least a week and prob- 

 ably longer, apparently without taking food ' (letter from Dr. Hagen). 



1 'Entomolog. Mag.,' vol. i. p. 527, 1833. 



