353 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 sete, 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 As the wings of the imago are withdrawn from the 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 branchiz, 
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 sete 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 Ephemeride or 
May-flies,’ the most modern and re- 
liable entomological work on the 
subject, the sete of the female in- 
crease from about 16-19 mm. in the subimago to 24-26 mm. 
in the imago, while in the case of the male the sete, 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 
IMAGO. 
