70 
INTRODUCTION TO 
Insecta, differ from them, in regard to external parts, 
in having a greater number of legs, the head soldered 
to the trunk, four antennae, (in the great majority) 
and the composite eyes usually raised on moveable 
footstalks ; and, in reference to internal structure, in 
possessing a complete circulation, and branchiae for 
respiration analogous to those of fishes. The only 
connection which the Annelides have with the pre- 
ceding classes, arises from their simulated structure, 
'the want of an internal skeleton, a similar nervous 
system, and in being oviparous ; in all other respects 
they are widely removed from them. Their blood 
is red, like that of the vertebrata ; the head is scarcely 
distinct, and there are no antennae properly so called ; 
none of them possess proper feet, and the majority 
are hermaphrodite. 
Besides these distinctions, special to each indivi- 
dual class of the articulatn, they all have this common 
difference from insecta, that they are destitute of 
wings, and do not undergo metamorphosis.* Their 
growth is gradual and insensible, during which many 
of them change their skins, but they preserve, with 
few exceptions, the same form they had at birth. 
Insects, on the contrary, pass through a variety of 
changes, during which they assume such dissimilar 
forms, that it is often impossible to recognise the same 
individual at different periods of its existence. The 
* This assertion, however, must not in one instance be made 
absolute, for in regard to the Crustacea, a certain kind of 
metamorphosis may be assumed as having been recently de- 
monstrated. 
