120 THE BUTTERFLY VIVARIUM. 



and by the action of the pectoral legs swims to the 

 surface. 



The escaping insect, as he emerges, uses the 

 pupa case as a kind of raft, on which it puts forth its 

 wings without injury from wet ; and by the time it 

 has completed its toilet, all traces of the mandibles, 

 by means of which the silken door of the prison was 

 cut open, have disappeared. This pretty Moth-like 

 insect undergoes yet another change, or extraordi- 

 nary kind of moult, before it is ready to pass in full 

 costume the two or three hours of existence assigned 

 to its winged state. This consists in divesting it- 

 self of an extra skin which covers the wings 

 and every other member, and which, when left on 

 the branch where the operation was performed, seems 

 so like the fly itself which has just quitted it, that a 

 careless observer would certainly be deceived, for 

 the deserted sheath is still an entire, unbroken piece. 



The Gnat is enabled to emerge from its chrysalis 

 without wetting, in consequence of a portion of the 

 corslet being covered with a greasy secretion, which 

 keeps it dry, and prevents the whole from sinking 

 while the Gnat escapes. It floats, though heavier 

 than the water, upon the same principle that a dry 

 needle does, for a short time. "When the shell first 

 opens and shows an interior skin still, which enve- 



