Mr. Garner on the Nervous System of Molluscous Animals. 499 
convinced, however, that there is a retina internal to this pigment. By drop- 
ping dilute nitric acid on its internal surface, after removing the hyaloid, this 
retina is made apparent. It immediately becomes white and opake, and is 
seen to be of considerable thickness, but, like the black coat itself, of the 
greatest softness and delicacy. It must, however, be confessed that no nerves 
are seen to go from the external retina to this; but their fineness may conceal 
them. The glandular mass at the bottom of the eye communicates externally 
by means of a duct which pierces the cartilage, deepening the edge of the 
orbit, and is seen to open externally beneath and behind the eye*. The ex- 
ternal opening does not, as is supposed, admit the rays of light. to the lens. 
In the living animal it is perfectly closed, and it ought to be considered as 
the excretory orifice of an anterior chamber. There is a round transparent 
part of the conjunctiva for the admittance of the light. The orifice is not in ` 
the axis of the lens; it is so small, that it is often difficult to discover; and it 
does not, in the living animal, prevent the existence of an aqueous humour 
before the lens-+. 
There are trifling differences in the nervous system of these Cephalopoda. 
Thus in Loligo the pedal ganglion is very anterior, whilst in Octopus it is 
scarcely separate from the rest of the brain. When there is no fin, as in the 
latter animal, the second division of the large nerves of the mantle is wanting. 
The author has not had an opportunity of examining Octopus, so that he 
cannot positively affirm that Cuvier has overlooked the labial, lingual{, and 
sympathetic ganglia, but he may mention that he has seen them in Sepia, 
Sepiola, and in Loligo communis and medius. 
The author needs only notice Mr. Owen's beautiful * Monograph" to ob- 
serve that the brain of the tetrabranchiate Cephalopoda must, from his de- 
seription, be little different from that of the Sepia, though less perfect. The 
superior cerebral lobe is not developed; and in this and other respects it is 
more nearly allied to the brain of the higher Gasteropoda. 
* The opening described by Blainville in the Loligo is probably the conjunctival pupil of Cuvier. 
t There is much confusion and difference in the descriptions of Cuvier, Blainville, and Carus. 
i This lingual or pharyngeal ganglion, however, though not described in the text, appears repre- 
sented by his engraver without any mark of reference being attached. The author finds no mention 
of these different parts in Scarpa, Tilesius, or Swammerdam. 
372 
