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IX. On the Structure of the Optic Lobes of the Cuttle-Fish. 
By J. Lockhart Clarke, F.B.S., &c. 
Received September 26, — Read November 15, 1866. 
The brain of the Cuttle-fish is enclosed in a cartilaginous case or skull, which is pierced 
by foramina for the passage of the nerves which it gives off. It consists of several ganglia 
closely aggregated and united around the upper end of the oesophagus, as shown in 
fig. 1, Plate X. Above the oesophagus,- the foremost or pharyngeal ganglion (a), which 
is much the smallest, is bilobed, somewhat heart-shaped, and closely applied, at the 
central line, to the junction of that tube with the large globular and powerful pharynx 
(b, b, h). Behind this ganglion, and joined to it by two nervous cords, is a large bilobed 
ganglion (c c), which is broader above than below. It rests on a kind of disk or collar- 
like layer of nerve-substance, which forms the roof of the ring or short canal (d) through 
which the oesophagus is transmitted. 
Below the oesophagus, and forming the floor of the canal (d) that transmits it, is a 
large and broad ganglion (e) which extends forward and is partially divided into an 
anterior and a posterior portion. The latter portion is connected along the sides of the 
oesophagus with the sz^ra-oesophageal ganglia, by means of bands which complete the 
oesophageal ring. It gives off nerves to the branchiae, to the viscera, to the mantle, &c. 
The anterior portion of -the suboesophageal mass supplies nerves to the feet and 
tentacles, and a connecting branch to the pharyngeal ganglion («). 
From each side of these cephalic masses, and connected as much, apparently, with 
the ganglia beneath the oesophagus as with those above it, springs the optic peduncle 
(/) which unites them with the large optic ganglion (g g). On its upper surface is a 
small pyriform tubercle attached to it by a short pedicle or neck. Each optic lobe is 
as large as the rest of the cephalic ganglia on both sides taken together, and bears a 
striking resemblance in shape to the human kidney. Fig. 2 represents the left one 
freed from the nerves in which it is enclosed. It is very convex on its outer side, with 
a deep notch on its inner side where the peduncle is attached. Its upper surface also 
is a little concave, and its under surface is convex in a corresponding degree. Every- 
where it is covered and entirely concealed by a thick stratum of optic nerve's disposed 
in flattened bands, which issue from all parts of its substance and proceed at once to 
the back of the eye (h), in a layer or kind of fan-shaped expansion (i i), which, like the 
optic lobe itself, is somewhat concave at its upper surface and a little convex below. 
As they enter the back of the eye the bands of the layer decussate ; those proceeding- 
form the upper surface (i 1 , right side of figure) sloping downward over the convex border 
