132 
THE VOYAGE OF H.M.S. CHALLENGER. 
connective. 1 Tlie lower half was connected with the upper on either side by two connectives ; 
it consisted of two pairs of ganglia lying upon each other, whose wide, broad commissure 
was about as long as the greatest diameter of the ganglia ; they were separated by the 
strong arteria bulbi pharyngei. The (three ?) pleural ganglia were somewhat smaller 
than the others, less flattened, and of transversely oval form ; in front of their 
commissure was the thin sub-cerebral commissure. From each ganglion four nerves, 
partly united at the base, were given off to supply the side walls of the body and 
the back ; one of these was especially thick, and extended backwards along the sides of 
the back. From each ganglion were given off two nerves, running along the sides of the 
posterior aorta as far as the anterior genital mass, giving off to it several branches, and 
finally reaching the hermaphrodite gland ; from one of the left nerves a strong branch 
went to the region of the anterior bile duct. From the right side of the visceral com- 
missure, near the ganglion, two nervi genitales arose, and were distributed to the vas 
deferens and the glandula hastatoria. The pedal ganglia , rather larger than the others, 
were of a rounded contour ; they gave off a short nervus pediaeus anterior, a nervus pediaeus 
medius externus, and a nervus pediaeus posterior longus, which entered the sole of the 
foot about the middle of its length, dividing into a superficial and deep branch ; from 
the latter arose numerous twigs directed obliquely inwards. A rope-ladder-like system, 
as first described by Semper 2 in opposition to v. Jhering 3 cannot, however, be dissected 
in situ. The buccal ganglia are of a rounded contour, and lie within a wide, but still 
rather adherent capsule united by a commissure (PI. Y. fig. 3, b), about double as long as 
the diameter of the ganglia ; the two nerves going off from them supply the salivary 
glands, the oesophagus, and the hinder portion of the bulbus ; upon them were ganglionic 
swellings ; from the middle of the commissure a strong dichotomously branching nerve was 
given off, running backwards. Sympathetic ganglia 4 were found here and there upon 
the viscera ; on the spot, where the arteria genitalis divides on the under surface of 
the anterior genital mass, there was a large white ganglion of oval contour and '3 mm. 
diameter. 5 
The summit of the rhinophore was invaginated about 1 '2 mm., and at the bottom of 
this depression was the eye; its greatest diameter was about '28 mm.; the lens was 
yellowish, the pigment blackish-brown. The fine optic nerve was given off as a branch 
from the upper part of the rhinophorial nerve. At the base of the eye, enveloping it, 
1 It would be of high interest to examine whether the Onchidia possess the mouth-lobe-ganglion of the 
Pulmonnta. 
2 Loc. cit.,j>. 481. 
3 IT. v. Jhering, Ueber die system. Stell. von Peronia, 1877, pp. 8, 9. 
4 According to Semper, the buccal commissure with its ganglia in the Gasteropoda represents the vagus of the 
Annrdides. Cf. P. E. Sarasin, Entwicklungsgesch. d. Bithynia tentaculata, 1882, pp. 56, 57. 
<■ Owing to the state of hardening of the central nervous system, it was impossible to investigate it fully. There 
appeared to be three pleural ganglia, of which the smaller right one and the median one were more nearly 
approximate. . i 
