824 
1 
CLASS XIII. 
The nervous system is largely developed in the Cephalopoda, and 
in most of the genera the central mass for the head (the cerebral 
mass) is enclosed in the cartilaginous ring, which we have already 
noticed. Beneath the cesophagus a considerable nerve-mass is situ- 
ated, which in Maztilus is divided into two transverse bands, one in 
front of the other. From the anterior portion of this central mass 
(or from the first of the two half-rings, situated under the cesopha- 
gus in Nautilus) the nervous trunks for the arms arise, or for the 
tentacles surrounding the head. In Octopus, Sepia, and Loligo, 
these anterior portions form on each side a large, flat ganglion, from 
the anterior margin of which the brachial nerves of that side radiate 
(ganglions en patte doie Cuvier), From the posterior portion arise 
at the side thick nervous stems for the mantle, which in Loligo, 
Sepia, Octopus, &c, terminate in two large ganglia, from which the 
nerves radiate at acute angles; in Nautilus these lateral ganglia 
stellata are wanting. In addition there arise from the middle of 
the posterior margin of this portion two nervous trunks, at first laid 
close together, from which the nerves for the viscera arise. From 
the portion situated above the cesophagus nerves arise for the mus- 
cular mass that surrounds the jaws, or these come from the ganglion 
of the sympathetic system placed above the cesophagus (ganglion 
pharyngeum) as in Sepia and Loligo. From the lateral commissures 
of this portion, by which it is connected with the central mass situ- 
ated beneath the cesophagus, the two remarkable optic nerves arise, 
which terminate in kidney-shaped ganglia; lower down arise the 
two short auditory nerves which penetrate into the cartilaginous 
ring of the head. The sympathetic nervous system has a ganglion 
(ganglion labiale) seated under the cesophagus, and one on the sto- 
mach formed by the union of two nervous stems. 
On the organs of sense in this order, what we have stated above 
(pp. 766—768) may be referred to. The skin of the Cephalopods is 
distinguished by a change of colour exhibited during the life of the 
animal, and depending upon a peculiar stratum of saccules filled 
with pigment-granules (chromatophores of SANGIOVANNI and WaG- 
NER), which are connected by a delicate, elastic, membranous tissue. 
These organs lie immediately under the cuticle, and by alternate 
contraction of the vesicles, containing red, blue, or yellow colouring 
matter, a lively play of colour arises in definite situations, especially 
in Loligo and Argonauta'. 
Compare R. WAGNER in OxKeEn’s Jsis, 1833, pp. 159—161, WIEGMANN und ERICcH- 
son’s Archiv f. Naturgesch. 1841, s. 35—38. 
