290 STATES OF INSECTS. 



bottom, — the thorax, which belongs to the heaviest half, 

 being the lowest ; and if the pupa be again brought to the 

 surface, so that the fluid is repelled from its disk, it re- 

 mains suspended there without effort, as before. Just 

 previously to the exclusion of the fly, the dry part of the 

 thorax is seen to split in the middle. The air enters, and 

 forms a brilliant stratum resembling quicksilver, between 

 the body of the insect and its puparium ; and the former 

 pushing forth its head and forelegs, like the gnat, rests 

 the latter upon the water, and in a few seconds extricates 

 itself wholly from its envelope. 



Before I close this letter, I must state a fact connected 

 with the subject of it that deserves jto be recorded. It is 

 a general rule, that one pupa-case incloses only one insect; 

 but Kleesius, a German entomologist, asserts that he 

 had once two specimens of Gastropacha quercifolia pro- 

 duced from owe pupa; which was large, being full two 

 inches long, and one thick. 



