Oct. 12, 1883 



* KNOWLEDGE 



231 



S: 



trunk of a tree, or to the stem of some water plant, and 

 cast oil' a thin membranous skin, which has enveloped the 

 body and wings ; and fly quickly away before the eyes of 

 the observer, leaving this skin resting upon the stem, look- 

 ing at first like a dead insect. After this operation the 

 wings are much brighter. The state between leaving 

 the water and casting oU'the skin is called "pseudimago." 

 These day flies were known to the ancients. Aristotle 



says " that about the time of the summer equinox lie ob 

 served on the shore of one of the rivers which empties 

 into the Bosphorus, little sacs, from which insects would 

 creep out and liy about until evening, then grow weary and 

 ilie at the setting of the sun. They were called on this 

 account day flies." 



On a quiet Jlay or June evening these insects may be 

 seen flying about, sometimes in great numbers, their gauze- 



