REPORT OjST THE PTEROPODA. 
25 
The figure of the nervous system of Cymbulia given by Souleyet 1 shows three 
ganglionic enlargements on the visceral commissure, whilst the text states only that “ la 
disposition du systeme nerveux est la meme que chez les autres Pteropodes testacds.” 2 
Now it has been shown that in these latter the nano-lia of the visceral commissure form 
o o 
a mass composed of two asymmetrical halves, more or less clearly separated. 
On the other hand, van Beneden 3 describes the elements of the visceral commissure 
as “ une paire de ganglions," whilst Gegenbaur 4 agrees with Souleyet in saying that the 
nervous system of Cymbulia resembles that of typical Thecosomata. Finally, von 
Jhering, the last who has studied these organs, describes and figures 5 the elements of 
the visceral commissure as fused with the pedal ganglia in such a way as to form two 
large symmetrical infracesophageal ganglionic masses, upon which the otocysts are 
placed. 
The investigation which I have made of the nervous system of Cymbulia e has shown 
that Souleyet’s figure is by no means complete with respect to the nerves which proceed 
from the visceral ganglia, but it is absolutely accurate as regards the number and dis- 
position of the ganglionic enlargements, that is to say, that there are three closely placed 
visceral ganglia, separated only by constrictions, and of which the outer are approximated 
to the cerebral ganglia (PI. IIP fig. 10, c, cl, e ). 
The two outer ganglia are symmetrical, the median is the largest (fig. 10, d ). It 
may further be seen (figs. 10 and 11) that the visceral ganglia are quite distinct from 
the pedal ganglia (b), in contradiction to what is stated by von Jhering. The central 
nervous system of Cymbulia, seen from the ventral surface, can only present the appear- 
ance attributed to it by the last-named author, before the surrounding connective-tissue 
has been removed from it. 
The nerves which arise from the visceral ganglia are four in number, as follows, — one 
springs from each lateral ganglion ( 1 and J), and two (not one only as depicted by 
Souleyet) which issue from the unpaired median ganglion (£ and 3). The stronger of 
these latter proceeds from the left of the ganglion, the more slender on the right 
side. 
The nerves of the lateral ganglia ( 1 and J) supply the mantle ; the nerves from 
the median ganglion proceed to the genital (3) and to the circulatory and excretory 
organs (£). 
The nerves from the other ganglia are distributed in the following manner : — 
From each cerebral ganglion arise three nerves (and not two as I stated formerly'); 
an incipient transverse segmentation, which recurs more clearly expressed in Gleba, may 
be observed in the cerebral ganglia (PI. III. fig. 11). From the dorsal segment proceeds 
1 Voyage de la Bonite, Zoologie, Mollusques, pi. xv. bis, fig. 38. 
2 Ibid., t. ii. p. 239. 3 Exercices Zootomiques, p. 11. 
4 Untersuchungen fiber Pteropoden und Heteropoden, p. 44. 6 Loc. cit., pi. v. fig. 19. 
6 Becherches sur le systeme nerveux des Pteropodes, Arch, de Biol., t. vii. p. 117. 7 Ibid., pi. iv. fig. 13. 
(ZOOL. CHALL. EXP. PART LXVI. — 1888.) U uu ^ 
