198 STATES OF INSECTS. (Larva.) 
than ever. When a few meals have invigorated its lan- 
guid powers, the renovated animal makes up for its long 
abstinence by eating with double voracity. 
A similar preparatory fast, and succeeding state of 
debility, accompany every change of the larva’s skin. 
Each time except the last, the old skin is succeeded by 
a new one, with few exceptions, similar to the one it 
has discarded. Previously to the final change, which 
discloses the pupa, it quits the plant or tree on which it 
had lived, and appears to be quite unsettled, wandering 
about and crossing the paths and roads, as if in quest of 
some new dwelling. It now abstains from food for a 
longer time than before a common moult, empties itself 
copiously, and as I have just said, if Swammerdam and 
Bonnet are to be depended upon, casts the skin that 
lines the stomach and intestines, as well as that of the 
Tracheee. 
I have observed above, that all larvae, with few excep- 
tions, change their skins in the manner that I have de- 
scribed. ‘These exceptions are principally found in the 
order Diptera, of which those of the Linnean genera 
Musca, Cistrus, and probably all that, like the maggot 
of the common flesh-fly, have contractile, or rather re- 
tractile, heads, never change their skin at all, not even 
preparatory to their becoming pupz. The skin of the 
pupa, though often differing greatly in shape from that 
of the larva, is the same which has covered this last 
from its birth, only modified in figure by the internal 
changes that have taken place, and to which its mem- 
branous texture readily accommodates itself. The larvee 
of the Dipterous genera T7pula, Culex, and those which 
have apparent corneous heads, like other larvae change 
