INHABITING MULTILOCULAR SHELLS. 35 
second provided with a muscular gizzard somewhat resembling in 
structure that of the crocodilean reptiles and rapacious birds. 
The nervous system of cephalopods shows more clearly than any 
thing else the near approach of the class to the vertebrata. We find 
a distinct brain, sometimes divided into lobes, enclosed in an organ- 
ized cranial cavity ; numerous symmetrical ganglia are developed on 
the great nervous axis, both before and behind that organ, and sym- 
pathetical ganglia are observed in the abdominal cavity. “ So that, 
although the brain of the cephalopods is still perforated by the ceso- 
phagus, as in all the inferior classes, we find all the principal parts 
of the nervous system of the vertebrata already developed in this 
class ; and after undergoing a series of changes of form and position 
in the inferior tribes of animals, regulated by the general develope- 
ment and form of the body, they have here acquired the form and 
situation which they preserve throughout all the higher classes.”* 
Having thus given a kind of outline of the most important points 
in the comparative anatomy of these animals, we now proceed to cou- 
sider the structure and importance of those shells, whether external 
or internal, which are, in most cases, the only means left us to deter- 
mine the nature of the animal once their possessor. In this part of 
the subject great caution is necessary; for there is danger both of 
giving undue importance to minor points, and also of neglecting some 
of those minutiz which sometimes really indicate a change of struc- 
ture to a considerable extent. 
The parts of cephalopodous animals found fossil consist of the 
shell, the jaws, and occasionally a kind of bag, or pen as it is called, 
which once contained a thick black fluid, to serve as a defence to its 
possessor, just as in our own seas the Squid, or Cuttle-fish, darkens 
the water about it, by a similar fluid, when it is desirous of escaping 
from an enemy. Of these remains it will be necessary to consider 
carefully the nature of the first—the shell, as it is by far the most 
commonly preserved, and seems to be, in many respects, the most 
clearly indicative of the nature of the animal inhabitant. In the ab- 
sence, also, of a more definite knowledge of the habits and appear- 
ance of this inhabitant, the shell remains the only means of classifi- 
cation. 
The structure of all the shells of this class of animals is always 
more or less cellular. In some, as the Cuttle-fish, the internal cal- 
careous skeleton (employed in the composition of tooth-powder and 
“ Qutlines of Comparative Anatomy, by Dy. Grant, p. 221. 
1 Y, YY } 
