INTRODUCTION. 
91 
and after it has been for a short time exposed to the 
air, it is ready for flight. 
Other minute ichneumons deposit their offspring 
in the eggs, or in the pupa of butterflies, and such 
numbers are destroyed in this way, that it is evident- 
ly one of the means employed by Providence to keep 
within due limits a tribe of creatures which, if left 
to propagate without restriction, would occasion in- 
calculable mischief, by destroying almost every kind 
of vegetable produce. 
Having thus attempted to sketch the general his- 
tory of Butterflies, a subject of sufficient extent to 
admit of much further detail, we now proceed to de- 
scribe the species which have been ascertained to 
inhabit Britain, reserving such additional historical 
notices as may be necessary for the full elucidation 
of the subject, till we come to treat of the genera 
and species to which they respectively refer. 
