MESSRS. HANCOCK AND EMBLETON ON THE ANATOMY OF DORIS. 231 
The first division corresponds to the excito-motor, or indeed to the cerebro-spinal 
system, the second to the sympathetic system, of the Vertebrata. These two systems 
in Doris are at several points distinctly in connection with each other, and all the 
ganglia of the two systems are in D. tuberculata at least, from which the principal 
description of the nervous system is taken, of a bright orange colour. 
The supra-oesophageal ganglia* of the first system are five pairs and a single 
ganglion, the pairs being symmetrically placed with regard to each other, and to the 
median line; and the single ganglion, not hitherto described, and which we shall call 
the visceral, lies on the right side. Of these, three pairs predominate in size, the 
anterior of which, or sensorial, the cerebroid of M. Blanchard, lie next the median 
line, across which they are connected, and are of a somewhat conical shape, the base 
forwards. Springing from about the middle of the anterior border, and from the 
upper surface of these, is a pair of ganglia corresponding to the pedunculate pair, 
which in EoUs we have called olfactory. In Doris they are almost sessile, and 
though in size much inferior to the cerebroid, are nevertheless of notable dimen- 
sions. They give off each a large nerve to supply the dorsal tentacles, the first pair. 
The next three pairs of nerves come off from the under surface of the anterior border 
of the cerebroid ganglia, external to the attachment of the first pair. They run 
forward and supply the muscles and the skin at the side of the channel of the mouth 
and the lips : the second of these pass to the oral tentacles. The fifth pair comes off 
close after the fourth, passes forwards and downwards, and soon divides into two 
branches ; one goes on to the under part of the channel of the mouth and lips, the 
other courses round under the buccal mass, and unites with the corresponding nerve 
of the opposite side, to form the first or anterior collar {k), which is slender and 
wide. External and close to, and of about the same size as the fifth pair, comes off 
a nervous trunk, which curving round the top of the oesophagus, joins the principal 
infra-oesophageal ganglion. This trunk, instead of being an ordinary nerve, consti- 
tutes with its fellow of the opposite side the second or middle collar (/) or commis- 
sure between the anterior supra-oesophageal and the larger infra-oesophageal ganglia, 
and for this reason we omit it in the enumeration of the nerves. The sixth pair are 
very short, and come off from two minute elliptical ganglia, almost sessile upon the 
external border of the anterior or cerebroid ganglia near their posterior end : these 
are the optic nerves and ganglia. The seventh pair of nerves appear to have no 
trunk, for the auditory capsule is sessile on the ganglia directly behind the optic 
nerve. 
The posterior or branchial ganglia are broadly ovate, and connected in front with 
both the cerebroid and the other pair. The eighth, ninth and tenth pairs arise from 
these ganglia, and are distributed to the whole of the mantle ; the two first of these 
pairs go to the anterior, and the last to the posterior portion, sending a branch of 
communication (10') to the branchial ganglia of the sympathetic system. The 
* Plate XVI. fig. 8. 
2 H 
MDCCCLII. 
