40 THE DURATION OF LIFE. [1. 



of September to the end of the month. In captivity they die 

 after depositing their eggs : the males are probably more 

 short-lived, for towards the middle and end of September they 

 are much less plentiful than the females. 



Acridium inigratorimn ' 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. 



Ephemeridae. Rosel, speaking of Ephemera vulgata (' In- 

 sektenbelustigungen,' Bd. II. der Wasserinsekten, 2*^ 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 insects 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.' 



Libellida. 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 saccharina. An individual lived for two years in a 

 pill-box, without any food except perhaps a little Lycopodiuui 

 dust ^ 



1 < 



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



