376 Mr. Robert Garner's Malacological Notes. 



below. The organs of siglit and smell, when tlicj exist, are 

 supplied by the labial or oral ganglia, which unite above in 

 the higher forms into what may be called, in this case, the 

 cerebrum or cerebral ganglion, whilst the acoustic sacs are 

 connected with the loAver ganglia. As we ascend, other gan- 

 glia, or centi'cs of nervous action, are formed; thus a sym- 

 pathetic system appears, of which the principal centre is a 

 large ganglion {Sepia), or several smaller ones {Doris), on or 

 near the stomach (gastric), connected through nerves running 

 along the alimentary canal with two or more (six in Doris) 

 small pharyngeal ganglia, situated on the buccal mass, and 

 through them witii the cerebral ganglia, and also having 

 branches connected with internal respiratory nerves, these last 

 forming one or more branchial ganglia at the root of the 

 branchiffi, and descending from the respiratory or lower and 

 hindmost part of the cerebral ring. Probably the small 

 pharyngeal or buccal ganglia exist in all Gastropods and 

 Cephalopods. Pallial or external respiratory nerves also 

 originate a little outside the internal ones, superadded to them, 

 and es])ecially belonging to the mantle, the inhalant and 

 expelling sac, and foniaing the remarkable star-like ganglia so 

 plainly seen on each side within the mantle in all dibranchiate 

 Cephalopods. This pallial nerve in the Sepia thus reminds 

 one somewhat of a spinal nerve, as it has ganglionic branches 

 for the sac and non-ganglionic ones for the fin. There are 

 special nerves from the same part of the cerebral centre for 

 the siphon. In the Cephalopoda these nerves, which supply 

 the branchiae and respiratory sac or mantle, internal and ex- 

 ternal respiratory, descend symmetrically from the cephalic 

 ganglion on either side the vent in front, and at an equal dis- 

 tance from the middle line. Bivalves, as well as Chiton and 

 Doris, agree in this symmetrical an-angement ; but in the 

 ordinary spiral Gastropods {Natica or Neritina for instance), 

 owing to the torsion of the mantle, the vent has risen to the 

 right side above the neck, the left pallial or external respira- 

 tory nerve has followed in the same direction under the oeso- 

 phagus, and the pallial ganglion, which it forms, is on the 

 right side, whilst the right nerve crosses over the digestive 

 canal to the left side preceding the right branchial appen- 

 dage, the left (often atrophied) remaining in position, as in 

 Nerita, or dwindled away. The pallial opening and also 

 the siphon are correspondingly displaced. Two branchial 

 nerves and ganglia (internal respiratory) exist, as already 

 mentioned, in the dibranchiate argonaut and cuttlefish^ with 

 two ganglia in the course of each nerve in the first ; but there 

 is but a single nerve for the single gill in many Gastro- 



