VIII MAY-FLIES 317 



are liberated, can be thus fertilised.^ Again, how is 

 it that I never saw the males fertilise the egg-clusters, 

 which had been laid on a cloth or napkin ? If the 

 female could be so mistaken as to lay her eggs where 

 they could not possibly be hatched, why should not 

 the males fertilise them in such situations ? 



" I prefer to suppose that the males unite with the 

 females, but that the act of union is very brief 

 Indeed, I have seen something of the sort, though 

 only by the help of lights held near the surface of the 

 water. I with others caught pairs of the Insects 

 which appeared to be attached. When holding a 

 napkin over my knees, I saw the males mount upon 

 the females and apparently unite with them. Lastly, 

 the male is provided with appendages near the 

 extremity of the abdomen which seem to be suitable 

 for grasping the female. 



" I do not know how long it takes for the eggs to 

 hatch, for those which I saved were put into a vessel 

 of water, which was not changed. Running water is 

 probably necessary. 



" The great fecundity of the females and the 

 sheltered situation in which the larvae dwell, explain 

 the extraordinary numbers of the winged flies. 

 Every year is not, however, equally prolific in swarms 

 of Ephemerae. The short duration of the winged 

 state requires the assemblage of great numbers of the 

 same species. If these Insects emerged a few at a 

 time and on many successive days, the males and 



Mt is pretty certain from subsequent observations that the 

 eggs of Ephemera; are fertilised in the body of the female 

 before thev are laid. 



