261 
Fig. 4 is taken from a dissection of the nervous system 
of Eledone cirrosa * Lamarck. The three principal pairs of 
nerve ganglia, namely, the cerebral, pedal, and parieto 
splanchnic, occur, as in the rest of the true Mollusca, but, 
being aggregated together, their connecting threads (com- 
missures) are not easily made out. 
In Fig. 4 are displayed the nerves of the arms (A A a), 
&c. ; the auditory nerves (b) ; the nerves of the funnel (c) ; 
the accessory nerve of the mouth (d) ; the pallial nerves (f) 
terminating in the singular bird-foot-shaped ganglia ; the 
branch of the visceral nerve to the muscles of the body (g) ; 
the ganglia of the branchial hearts (h) ; and the branchial 
ganglia (i). The nerves of the eye (optic) are largely developed. 
The Cephalopoda are divided into two orders : the Di- 
hranchiata furnished with two gills, and the Tetrahranchiata 
having four gills ; the Dihranchiata are divided into two 
groups : the Odopoda, including Cuttle Fish, with eight 
arms only, and the Decapoda, provided with eight brachia 
and two tentacles — ten arms. 
Having briefly enumerated the salient structural char- 
acters common to the class, we proceed to note some of tlie 
variations which occur in the lesser groups : — 
The Mantle. — This is the external skin which protects 
the viscera ; in the naked forms it is usually tolerably thick 
and tough, but in the shell-bearing Nautilus, it is soft and 
membranous. 
Chromatophores. — The Cuttles, Squids, and Argonauta have 
the skin provided with singular bodies called chromatophores: 
these are cells filled with pigment which, by means of 
radiating muscles, can be made to contract or expand at will, 
and thus blushes of varying hues may be made to play over 
the skin's surface ; the most general colour is that of the ink 
* For this and several other spocies of ]'ritish Cephalopoda a\ hich ndoru my 
collection, I am iudobted to tho dibintcrosted liberality of T. Moore, Esq. , LivorpooL 
