DORIS. 



in D. repanda and D.pilosa (fig. \p, p), it is also very extensive; but in D. tuberculata (PI. 2, 

 fig. 1 q,.q) the arrangement of these vessels is probably much simpler, little more than the 

 main trunks being visible. The cavity, too, in this species is more branched than usual. 



The nervous system of Doris comprises two portions : — a cephalic or cerebral, and a 

 sympathetic or organic. The cephalic, in D. tuberculata, is of an orange colour, and is made 

 up of two series of ganglia, supra- and infra- oesophageal, with their commissures and 

 numerous nerves. The supra-cesophageal ganglia are five pairs, and a single ganglion ; the 

 pairs being symmetrically placed with regard to the median line. Three pairs predominate 

 in size. The anterior or sensorial (PI. 2, fig. 13 a, a), the cerebroid of M. Blanchard, lie next 

 the median line, across which they are connected ; they are pyriform, with the broad end 

 forward. Springing from about the middle of the anterior border, and from the upper surface 

 of these, is a pair of ganglia (d, d), corresponding to the pedunculated pair of Eolis, — the 

 olfactory. In Boris they are nearly sessile; and though in size much inferior to the cerebroid, 

 are nevertheless of notable dimensions. They give off each a large nerve to supply the dorsal 

 tentacles, which constitute the first pair. The next three pairs come off from the under 

 surface of the anterior border of the cerebroid ganglia, external to the attachment of the first 

 pair ; the second and fourth run forward and supply the muscles and skin at the side of the 

 channel of the mouth and the lips. The third passes to the oral tentacles. The fifth pair comes 

 off close to the fourth, and soon divides into two branches ; one goes on to the under part of 

 the channel of the mouth and lip, the other courses round under the buccal mass, and unites 

 with the corresponding nerve of the opposite side to form the anterior collar (y), which is 

 slender and wide. External and close to the fifth pair, comes off on each side a nervous 

 trunk, which, curving under the oesophagus, joins the principal infra-cesophageal ganglia. 

 This trunk constitutes the second collar (h). The nerves of the sixth pair are generally very 

 short, and come off from two minute elliptical ganglia, almost sessile, upon the external border 

 of the cerebroid ganglia ; these are the optic nerves and ganglia. The seventh pair of nerves 

 appear to have no trunks, for the auditory capsules are sessile upon the same ganglia 

 immediately behind the eyes. 



The posterior or branchial ganglia (b, b) are, when distinct, broadly ovate, and connected 

 with both the cerebroid and pedial ganglia. The eighth, ninth, and tenth pairs of nerves 

 belong to the branchial ganglia, and are distributed to the whole of the mantle ; the tenth 

 sending a branch of communication to the branchial ganglia of the sympathetic system. 



The lateral or pedial ganglia (<?, c) lie on a plane beneath the others, with both of which 

 they are connected; and are generally in shape and size like the branchial. Three large 

 nerves, the eleventh, twelfth, and thirteenth pairs, pass off from these centres, and are for the 

 supply of the whole foot. Two small ones, the fourteenth and fifteenth pairs, appear to emerge 

 also from the same, and go to the sides of the body, between the mantle and foot. 



The single supra-cesophageal ganglion, which we propose to term visceral, on account of 

 its nerves being in connexion with the ganglia of the viscera, is round, scarcely so large as 

 the olfactory, and sessile on the under surface and anterior border of the right branchial 

 ganglion, where it is in contact with the pedial. Four nerves (j,k,l,m) issue from this 

 ganglion ; these go to the organs of reproduction, to the stomach, to the two hearts, and to 

 the branchiae, and can be traced, as has been just pointed out, into ganglia of the sympathetic 

 system belonging to these several organs. The only other nervous trunk in connexion with 



