10 
THE VOYAGE OF H.M.S. CHALLENGER. 
The infraoesophageal portion of the nervous centres (PI. I. fig. 8) consists of two 
portions : an anterior, pedal, and a posterior, visceral. The pedal group (b) is composed 
of two large symmetrical ganglia, pressed one against the other and in juxtaposition with 
the corresponding cerebral ganglia. On the posterior margin of each is an otocyst (e). 
The visceral group consists of two ganglia, each of which is also approximated to the 
cerebral ganglion of its own side ; they are, however, asymmetrical, inasmuch as the 
right ganglion (c) is much larger than the left ( d ), and the groove which separates them 
does not lie in the middle line of the body, but is displaced towards the left. The rule 
of Lacaze Duthiers, 1 according to which, in sinistrorsal Gastropods, the left half of the 
visceral commissure is the more developed, does not therefore hold good in the 
present case. 
This asymmetry was unobserved by van Beneden and Souleyet, and has not since been 
recorded, although it is very striking ; van Beneden 2 figures two symmetrical ganglia, 
and Souleyet 3 a single symmetrical ganglionic mass as in Gavolinia. 
(1) Cerebral Ganglia. — From the anterior portion of these ganglia proceed the 
nerves which supply the head and tentacles (PI. I. fig. 7, i). They probably 
also give origin to the auditory nerves which proceed to the octocysts, as 
is observed in all other Mollusca, and as I have also seen in certain 
Thecosomatous and Gymnosomatous Pteropocls, as I shall show further 
on ; I have not, however, been able to make out this nerve in Limacina. 
(2) Pedal Ganglia. — These give origin at their anterior aspect to large nerves 
passing to the foot and the fins (PI. I. fig. 8 ,f); a branch of the nerve to 
each fin goes to the little lobe which is found on its anterior border in 
certain Limacinse. 
(3) Visceral Ganglia. — These ganglia are asymmetrical not only in point of size 
but also in the nerves which proceed from them ; from the large ganglion 
on the right proceed three nerves, only one from that on the left. 
(i.) Right Ganglion. — The outer nerve (1) passes to the right side of the 
mantle and to the osphradium, and is probably homologous with the 
branchial nerve of Gastropods ; the two median nerves ( % , 3) supply the 
viscera (heart, kidney, and generative organs). 
(ii.) Left Ganglion. — The single nerve (4) goes to the left side of the 
mantle. 
The preceding description relates to Limacina helicina. In the small forms 
(“ Spirialis” of Souleyet) the disposition of the nerve centres is the same. Souleyet 4 
1 Du systeme ri erveux des Gastdropodes pulmones aquatiques, Arch, de Zool. Exper., ser. 1, t. i. p. 494, No. 13. 
2 M4moire sur la Limacina arctica, MAm. Acad. Sci. Bruxelles, t. xiv. pi. v. figs. 7, 13. 
3 Voyage dela Bonite, Zoologie, Mollusques, pi. xi. fig. 21. 
4 Ibid., t. ii. p. 213. 
