18 
INTRODUCTION. 
selves in the winged state, deposit their eggs among plant-liee, 
upon the blood of which their young afterwards subsist. Many 
{^Conopidce, excluding Stomoxys, Tachince, Ocypterce, Phorce, &c.) 
lay their eggs on caterpillars, and on various other larvae, within 
the bodies of which the maggots hatched from these eggs live till 
they destroy their victims. And finally others {Anthracidce and 
Volucellce) drop their eggs in the nests of insects, whose offspring 
are starved to death, by being robbed of their food by the off¬ 
spring of these cuckoo-flies. Besides performing their various 
appointed tasks in the economy of nature, flies, and other insects, 
subserve another highly important purpose, for which an all-wise 
Providence has designed them, namely, that of furnishing food 
to numerous other animals. Not to mention the various kinds of 
insect-eating quadrupeds, such as bats, moles, and the like, many 
birds live partly or entirely on insects. The finest song-birds, 
nightingales and thrushes, feast with the highest relish on maggots 
of all kinds, as well as on flies and other insects, while the warblers, 
vireos, and especially the fly-catchers and swallows, devour these 
two-winged insects in great numbers. 
The seven foregoing orders constitute very natural groups, 
relatively of nearly equal importance, and sufficiently distinct 
fi’om each other, but connected at different points by various 
resemblances. It is impossible to show the mutual relations 
of these orders, when thev are arranged in a continuous se- 
ries, but these can be better expressed and understood by 
grouping the orders together in a cluster, so that each order 
shall come in contact with several others. 
Besides these seven orders, there are several smaller 
groups, which some naturalists have thought proper to raise 
to the rank of independent orders. Upon the principal of 
these a few remarks will now be made. 
The little order Strepsiptera of Kirbv, or Rhipiptera of 
Latreille, consists of certain minute insects, which undergo 
their transfoiTnations within the bodies of bees and wasps. 
One of them, the Xenos Peckii. was discovered bv Professor 
Peck in the common brown wasp (^Polistes fascata) of this 
