358 SALMON AND TROUT. 



some solid body, such as a wall, or post, or bough of a tree ; 

 its outer skin is then distended and splits up the back, the head 

 and legs are drawn out, then. the abdomen and setae, and lastly 

 the wings. As the wings of the imago are withdrawn from the 

 outer skin which formed the exterior surface of the subimago 

 wings, these latter collapse at once, so that the exuvium left by 

 the imago has, to a certain extent, the same outward appear- 

 ance as the nymph-shuck, the most apparent distinction be- 

 tween them being the presence on 

 the nymph-shuck of the branchiae, 

 arranged on each side of the back 

 of the abdomen at the joints. 



The hairs with which the surface 

 and margins of the sub -imago wings 

 were covered are absent from the 

 imago ; the setae and forelegs in this 

 last metamorphosis have become 

 much longer, and this increase is 

 more marked in the males than in 

 the females. Thus, according to 

 the dimensions given in the Rev. 

 A. E. Eaton's * Revisional Mono- 

 graph of Recent Ephemeridae or 

 May-flies,' the most modern and re- 

 liable entomological work on the 

 subject, the setae of the female in- 

 crease from about 16-19 mm - i n tne subimago to 24-26 mm. 

 in the imago, while in the case of the male the setae, in the 

 subimago measuring from about 17-21 mm., extend to as much 

 as 36 or even 41 mm. in the imago. 



The male imagines are seen dancing up and down in the 

 air in clouds, and the moment a female appears a number of 

 them start in pursuit of her. Sexual intercourse takes place in 

 the air during flight, the male lowermost. To quote the words 

 the Rev. A. E, Eaton : 



' Darting at his mate from below, and clasping her prothorax 



