118 MOLLUSCA. 
CHAPTER III. 
SYSTEMATICAL DISTRIBUTION OF THE MOLLUSCA.- 
Tue successful methodical disposition of molluscous ani- 
mals, could not have been accomplished previous to labours 
similar to those of Cuvier and Lamark; or until the shell 
and the contained animal were studied as connected objects. 
When thus contemplated, molluscous animals admit of ar- 
rangement into two great classes, or divisions, which may 
be distinguished from each other by well-defined characters. 
In the one, the presence of a head may be recognised, to- 
gether with eyes, and even ears in some of the groups. In 
the other, containing animals much less perfect in their or- 
ganization, there is no head, neither vestige of eyes or ears 
in any of the species. The former have been termed Mol- 
lusca Cephala, the latter Mollusca Acephala. This ar- 
rangement was first employed by Baron Cuvier, and after- 
wards by Lamark and other modern systematical writers. 
In the last work of the former naturalist, this method is de- 
parted from, and the six classes to which we have already 
referred, are constituted of equal rank, instead of being 
placed in subordination to the two primary divisions under 
which they can be suitably distributed. 
