824 CLASS xin. 



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 oesophagus a considerable nerve-mass is situ- 

 ated, which in Nautilus 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 oesopha- 

 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 d'oie 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 oesophagus nerves arise for the mus- 

 cular mass that surrounds the jaws, or these come from the ganglion 

 of the sympathetic system placed above the oesophagus (ganglion 

 pharyngeurti) 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 oesophagus, 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 oesophagus, 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 1 . 



1 Compare R. WAGNER in OKEN'S Isis, 1833, pp. 159 161, WIEGMANN und ERICH- 

 SON'S Archivf. Naturgesch. 1841, s. 35 38. 



