EPHEMERA. 
373 
The larva, which is supposed to continue two years 
at the bottom of the water, is about an inch long, 
and is furnished with several lateral appendages 
like fins ; it has likewise three bristles at the tail, 
which are equal in length to the whole body. The 
change from the larva to the perfect insect, which 
in many of the tribe is both a painful and laborious 
operation, is effected by this little animal with the 
greatest ease. When the time approaches for the 
change to take place, the inhabitant of the water 
rises to the surface, its skin bursts, and from the 
cavity thus formed issues the fly, whose wings are 
immediately unfolded, and the new insect launches 
into the air, quitting for ever an element which is 
no longer congenial to its nature. After this it 
quits a second skin, and becomes a perfect ephe- 
mera. Myriads are thus produced, who sport about 
the banks of the river for a short time, and then fall 
to the ground. Their numbers are so incredible 
that they form a thick crust upon the earth where 
they fall, and we are told by Scopoli that the coun- 
trymen in the duchy of Carniola carry them into 
the fields for the purpose of manure. 
The larvse of this, as well as of others of this 
genus, form tubular hollows in the banks of rivers. 
These are so numerous, that the banks of some 
rivers are quite studded with them, and they are 
made like syphons, with two holes, through which 
the insect has free admission. As it is necessary 
that these habitations should be always under the 
