THE EPHEMERIDZ. 353 
This is curious enough, for it is not often that the degraded 
condition so commonly observable in the wings of female insects 
is to be found in the males, and it is very interesting that such 
closely-allied insects should have such remarkable differences of 
structure, 
The Ephemeride exist in enormous numbers, and last for the 
shortest time imaginable in their perfect state. They are the 
lightest, the most fragile, and the most delicate creatures in the 
world. They float away in the air from off the water, in which 
they have lived during the early stages of their existence, flutter 
in the sunshine, dance about with every breeze, and they grow 
faint as the sun gets low, and sink and die with the night. 
They are truly ephemeral beings. They can be easily dis- 
tinguished. They have very short antenna, ending with an 
extremely delicate silk-like thread ; their wings are very fine, the 
front ones are the largest, the hind ones being very small; the 
body is terminated by two or three long-jointed bristles; the 
structures of the mouth are soft, and cannot receive food, and 
indeed the perfect insects, living as they do only a few hours, 
never think of wasting their lives in eating and drinking. They 
all exist for love, and they spend their short day in a constant 
and active courtship. The eggs are laid in little packets upon 
the water. As soon as the larve escape from the egg they take 
to the water, and grow more or less rapidly, according to the 
species. These larve are essentially aquatic insects, and are 
organised so that they can respire in water, for there are gills, or 
delicate folds of skin, which are traversed by numerous tracheze 
fixed on to their bodies. The larve of all the species of the 
genus L:phemera are very similar, and they are believed to live 
two or three years before they begin their transformations. They 
reside beneath stones or in burrows at the bottom of running 
streams, and they undergo an incomplete metamorphosis. They 
have very strong jaws covered with spines, and mandibles with 
sharp points to them. They begin to be nymphs when the rudi- 
ments of wings appear. When the nymph is full grown, it crawls 
out of the water on to plants or stones, and its skin cracks 
down the back and the adult emerges from it into the air. But 
this perfect insect is covered over and entirely enclosed in a 
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