MESSRS. HANCOCK AND EMBLETON ON THE ANATOMY OF DORIS. 
233 
pair which passes off backwards to the base of the tongue, and is joined by buccal 
filaments of the sympathetic. To the front of the buccal are attached the gastro- 
oesophageal ganglia, which are very small and give off three pairs of nerves. The 
smallest of these, the nineteenth pair, is given to the salivary gland. The twentieth 
supplies the top of the oesophagus, round which it curves on each side, communi- 
cating with the oesophageal sympathetic plexus. Lastly, the two nerves constituting 
the twenty-first pair, by far the largest of the three, are continued down on the 
under surface of the oesophagus, on each side of the median line, nearly parallel with 
each other, communicating by slender filaments with a fine open network of nerves 
and ganglia upon that tube, and unite with two of the largest ganglia of the sympa- 
thetic system of the stomach. This pair is the counterpart of the gastric portion of 
the par vagum of the higher animals, and is analogous to the nerves which in insects 
have been named stomato-gastric. 
The principal varieties that have been observed in the cerebro-spinal nervous 
centres are as follows ; in D. pilosa* and D. repanda^, the first three pairs of 
ganglia are very distinct, and only slightly altered in relative position from those in 
D. tuherculata, the pedial becoming quite lateral as regards the oesophagus, and 
indeed almost meeting under that tube, the third collar being consequently of ex- 
treme brevity. In Z). tlohnstoni'^, D. verrucosa^, D. coccinea, D. hilamellata\^ and 
D. aspera, the cerebroid and branchial are more or less fused into one mass, which 
in some of the species is elongated in the antero-posterior direction, and in others 
obliquely. In D. Johnstoni^ the visceral ganglion is pedunculate; no material 
variation in the origin and distribution of the nerves has been observed. The visceral 
ganglion is present in all. 
The two pairs of infra-oesophageal ganglia just described, have been noticed in 
the Annales des Sciences Naturelles for 1848, by M. Emile Blanchard, in an article 
on the Opisthobranchiate Mollusks ; the larger pair he names oesophageal, and gives 
all their branches to the alimentary apparatus ; the smaller he calls angeiens or 
aortiques ; these latter he announces as a new discovery, and states that they are 
placed on ^each side of the aorta to which they give filaments. The corresponding 
ganglia in Eolis were discovered by us in 1846, and are to be found described and 
figured in the third part of the Monograph on the Nudibranchiate Mollusca, pub- 
lished by the Ray Society in tiie following year. These branches have now been so 
often verified by us, both in Eolis and Doris, that we are quite satisfied of the truth 
of the account we have given of them. We cannot therefore see the propriety of the 
names that M. Blanchard has imposed upon these ganglia. Further, M. Blanchard 
looks upon the infra-oesophageal ganglia and nerves as the representatives of the 
splanchnic or sympathetic nervous system of the higher animals ; and anatomists in 
general seem to have a confused idea that the oesophageal ganglia of the Mollusca, 
* Plate XVII. fig. 8. f Plate XVII. fig. 9. t Plate XVII. fig. 2. 
§ Plate XVII. fig. 4. y Plate XVII. fig. 6. II Plate XVII. fig. 3. 
2 H 2 
