112 
LECTUUE IX. 
of about half an hour the change is complete, 
and the same animal which before that time would 
have been killed by any long exposure to the 
air, would now be as effectually destroyed by 
submersion under water. 
The celebrated Insect called the Ephemera 
belongs to this Order, and proceeds likewise from 
an aquatic larve. The common May-Fly or 
Trout-Fly is a species of Ephemera, which 
emerges from its chrysalis chiefly in the month 
of May. But the most celebrated animal of the 
genus is that described by the famous Swammer- 
dam and held up as the most curious instance 
of the brevity of animal life, since, when one 
arrived at its complete or perfect form, it lives 
only about six hours. It must be recollected 
however that the animal has lived three years in 
its former or lava state, so that its brevity of life is 
only to be referred to that of its complete or 
perfect form. The size of this remarkable animal, 
which is not a native of England, but is common 
in many parts of Europe, is given on the plate we 
are viewing. Its colour is wdiite, with a yellowish 
body, and the larva is of a pale brown. 
The Insects of tliis genus have one particu- 
