314 NATURAL HISTORY OF AQUATIC INSECTS CH. 



" The Ephemerae issue from the water in order to 

 perpetuate the species. As soon as they emerge, the 

 females are ready to lay their eggs, and actually do 

 so. The rapidity with which they cast the larval 

 skin is truly wonderful. We cannot take our arm 

 from the sleeve of a coat more readily than the 

 Ephemeras extricates its abdomen, wings, legs, and its 

 long tail-filaments from their sheaths. During the 

 operation they rest upon objects standing out of the 

 water or upon the water itself The thorax splits 

 lengthwise, and the rest of the business of extrication 

 is over in a moment. I have often tried to stop it 

 half-way, in order to see how the wings are folded in 

 their sheaths. But though I crushed the head as soon 

 as it appeared, the act of emergence went on all the 

 same. So also when I plunged emerging Ephemeras 

 into spirits of wine, they completed their moult before 

 perishing. The long tail-filaments are often broken 

 durins: extrication. The cast skin is sometimes 

 carried up into the air, clinging to the tail-filaments, 

 and an Ephemera in this state seems twice as long as 

 usual. 



" The fly of Polymitarcys virgo is about three- 

 quarters of an inch long, not counting the long tail- 

 filaments. The hind wings are very small in com- 

 parison with the fore wings, which are in outline like 

 those of many Butterflies, though they are not scaly, 

 but transparent. The fore legs are very long and 

 directed forwards,^ the others short, perhaps too short, 

 for the fly cannot readily rise from a flat surface and 



1 Probably, as in other Ephemerae, these long fore legs are 

 used bv the male to seize the female. 



