THE OPTIC LOBES OE THE CUTTLE-EISH. 
159 
nervous cords, has also a composite structure. Its superficial, smooth, and convex 
portion consists of two comparatively thin caps or shells, joined in the middle line, but 
separated in front by a notch (see fig. 10, cc). It is composed of a very close inter- 
lacement or network of the finest fibres, interspersed with fine granules, with nuclei, and 
with small cells of different shapes ; and in these respects bears a strong resemblance to 
the cerebral lobes of fishes. Beneath the convex caps is a large mass of an entirely 
different structure. This consists of a kind of plexus, or interlacement of coarser fibres 
in every direction, with intervening but irregular and coalescing groups of nucleated 
cells and nuclei. It has some resemblance to that of the central parts of the optic 
lobes, but is finer. At its base, where it overlays the canal for the oesophagus, it presents 
a somewhat diversified appearance, and projects in front ( 3, fig. 10) and behind (fig. 1, 3) 
in the form of a kind of collar, as already stated. Whether this central portion of the 
ganglion constitutes any part of the nervous apparatus for vision, or whether it should 
be considered as a cerebellum, is not easy to determine. It is certainly in connexion 
both in front and behind with the optic peduncles and lobes ; but then so is the cere- 
bellum in vertebrate animals, especially in fishes ; and it can scarcely be expected that 
a distinct cerebellum would be wanting in an animal whose cerebral development 
approaches so closely to that of fishes in which that organ is very large. 
-The posterior part of the suboesophageal mass, as already stated, gives off nerves which 
supply the branchiae, some of the viscera, and the auditory apparatus, and may therefore 
be considered as homologous with the medulla oblongata ; while the anterior part, which 
supplies nerves to the feet and tentacles, may be regarded as the spinal cord, concentrated, 
like those organs, in the neighbourhood of the head. 
