70 INTBODUCTION TO 



Insecta, differ from them, in regard to external parts, 

 in having a greater numher 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 fop 

 respiration analogous to those of fishes. The only 

 connection which the Annelides have with the pre- 

 ceding classes, arises from their annulated 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 articulata, 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. 



