50 
THE VOYAGE OF H.M.S. CHALLENGER. 
1. Of the three first named the one nearest the middle line is directed forwards and 
divides into two principal branches which innervate the dorsal and middle 
cones. 
2. The middle nerve as soon as it issues from the ganglion gives origin to a strong 
thread passing to the anterior tentacle. Farther on a more slender branch 
springs from this nerve and gives off two branches, which innervate the lateral 
parts of the head and the retractor muscles of the buccal cones and of the 
anterior tentacle. 
The main trunk further gives off a branch distributed to the hood covering 
the head, to the lips, and finally to the ventral cone ; before entering which it 
exhibits an anastomosis with the nerve to the middle cone. 
Yon Jhering describes the nerves of the buccal cones as having each a 
ganglion united by commissure with the nerves of the two neighbouring cones ; 
that is to say, they have a disposition identical with that observed in the brachial 
nerves of the Cephalopoda. This is, however, quite erroneous ; not one of the 
nerves to the cones presents a ganglion on its course. As for the “ commissures ” 
said to exist between these ganglia, I have never been able to observe anything 
more than the anastomosis indicated above between the ventral and middle 
cones ; this is oblique and has none of the characters of a regular commissure. 
« 
3. The lateral nerve, more slender than the preceding, passes round the buccal mass, 
and innervates the false lips, a pair of swollen pads situated at the base of the 
buccal cones. 
4 and 5. The two nerves which arise from the dorsal surface of the cerebral ganglion 
and pass to the posterior tentacle, behave like the corresponding nerves of other 
Gymnosomata ; that is, they are optic and olfactory nerves, each ending in an 
enlargement. 
Wagner 1 regards the terminal enlargement of the optic nerve as the olfactory 
ganglion. Now the constitution of the swelling at the end of the other nerve 
shows that it is the olfactory ganglion or rhinophore ; in fact it gives rise to a 
rather large number of small nerves which become -lost in the extremity of the 
nuchal tentacle ; this is well known to be a character of the olfactory ganglion 
of the Gastropoda. On the other hand, the other swelling is comparable with 
the corresponding enlargement in the other Gymnosomata, in which, especially 
in Pneumonoderma, may be recognised the component parts of a rudi- 
mentary eye. 2 
The pedal ganglia are constituted as in the preceding Gymnosomata. Their second 
1 Die Wirbellosen des weissen Meeres, Bd. i. pi. xii. fig. 2, gn.2. 
2 Pelseneer, The Cephalic Appendages of the Gymnosomatous Pteropoda, Quart. Journ. Micr. Sci., 1885, pp. 
494, 495. 
