138 Mr. J. W. Duiiiiing on 



discovered to be very easy to separate the female pup^ * 

 from those of the male, by the external characters." I 

 think, therefore, that we must take it to be a fact, that 

 the wingless or stumpy- winged female is a natural form. 



The mode of coition of the winged female does not 

 appear to have been observed ; but Reutti, as recorded 

 by Heineraann, reports that the wingless female swims 

 on her back under the water by night, that coition takes 

 place in the water, the female laying hold of the male, 

 and drawing him down with her. 



Milliere and Peyerimhoff (Mill. Iconog. iii. 161) are 

 sceptical as to this, and, no doubt, it is, at first sight, 

 improbable. But let us see if there be not some corro- 

 borative evidence. 



In the first place, be it remembered, that the pupa is 

 under water, so that the moths, both male and female, 

 are born in the water. Then Kolenati says, " I saw one 

 female dive, and crawl down the stem of the Potamo- 

 (jetun," and I shall, hereafter, have occasion to show that 

 this was, in all probability, a winged female. Ritsema 

 expressly mentions that the males settled on the water, 

 " or on floating plants below." Brown saw the male " on 

 one occasion deliberately enter the water, and after 

 creeping down a pond-weed stem for an inch or two, it 

 emerged again with unwetted wings ; this act was pro- 

 bably done in pursuit of the virgin female ; " and again, 

 referring probably to this same occasion. Brown writes 

 (m Liu., 5th Oct., 1871) " I have also seen the male deli- 

 berately enter the water, which must, I should think, be 

 for no other purpose than that of searching for the apter- 

 ous female." M'Lachlan infoi-ms me, that at Hampstead 

 (where the only females captured were winged females) , he 

 frequently noticed that specimens drawn below the surface, 

 either on the net, or on patches of floating weeds, came 

 up again none the worse for their submersion. Barrett 

 reports that, if accidentally immersed, they " took no 

 notice whatever of the ducking." And Corbin says " it 

 is truly a water insect, as often only its head is above the 

 surface." It seems, indeed, to be common ground with 

 all who have had frequent opportunities of observing it, 

 that the male is constantly on, or (at least partially) in, the 



* Westwood's drawings (mentioned at p. 130, n.) corroborate this. 



