112 LECTURE 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 white, with a yellowish 

 body, and the larva is of a pale brown. 



The Insects of this genus have one particu- 



