AND DISTRIBUTION OF THE FIROLIDA. 261 
and tunic, the majority running from behind forward, and doubtless derived principally 
from the cephalic ganglion. i . 
2nd. The cephalic ganglion (Plate XLIII. figs. 1 & 8, f), situated between the eyes 
about the anterior third or fourth of the body, is the most distinctly bilobed, each half 
(fig. 8) being oval, prolonged, and pointed anteriorly, at least thrice the size of the entire 
buccal ganglion, and united with its fellow by a thick commissure. The cords given off 
are symmetrical, and distributed in three ways, viz :— 
€. Nerves for the organs of special sense, the eye, auditory vesicle, tongue, and 
tentacles. - : 
6. Intercommunicating cords, which unite the ganglion with the buccal in front, 
and the pedal behind. 
c. Ordinary nerves, for the cesophagus, muscular envelope, tunic, &c. 
The optic nerves (fig. 8,7) are short but thick, and originate in the outer and pos- 
terior part of each lobe by a broad base, which soon tapers into a cylindrical cord that 
runs outward, swells, and forms a cup-shaped cavity (fig. 8, Æ), which embraces, before 
entering, the eye posteriorly, to expand into the retina. Well-marked constrictions 
separate these protuberances (from which the optic nerves arise, fig. 8, A) from the prin- 
cipal mass of the ganglion; and we may regard them as distinct “optic lobes," both on 
aecount of their size and their containing nerve-cells like those seen in the main mass, of 
which they are in fact mere prolongations or appendages. 
The auditory, like the optic nerves, are large in comparison with the organs to which 
they are sent, and arise on either side (Plate XLIII. fig. 8, m) from the posterior part of 
the optie lobe by a single cord, which runs outward and backward to enter and become 
expanded on the capsule of the auditory vesicle (fig. 8, a k) ; but the mode of its ultimate 
distribution requires elucidation. It occasionally gives twigs to surrounding tissues 
(fig. 8). The minute structure of the optic and auditory nerves shows merely the usual 
hyaline interior, enveloped in a cylindrical sheath ; and in neither can any peculiarity be 
observed to mark their special character, or distinguish them from the ordinary motor 
Or sensory nerves of the body. | 
A. smaller nerve (Plate XLITI. fig. 5, e) usually arises on either side from the front of 
the cerebral lobes and inside the cerebro-buccal cords, runs a distinct course along the 
esophagus without communicating, and is lost apparently in the salivary glands, but 
possibly ends in the tongue as the nerve of taste. The specially endowed tactile organs, or 
tentacles, are each supplied with a comparatively large branching nerve (Plate XLIII. 
figs. 1 & 8, ah) from the outer and anterior aspect of the cephalic ganglion, which sends 
off lateral filaments and finally ends near the tip. 
The lobes of the cephalie are united to the buccal ganglion in front, and to the pedal 
behind, by large nerves, viz. :— ic : 
. a. The cephalo-buccal (Plate XLIII. fig. 5,7) arise on either side from. the anterior 
prolonged part of the cephalie lobe as a single cord (fig. 8, b) which runs along the ali- 
mentary canal, giving off side branches to it and adjacent tissues of the muscular and 
external coats, till near the buccal mass, where they bend upward to embrace the ceso- 
phagus, and then divide close to the ganglion into two, the larger of which, as already 
