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-f-. 



There are trifling diflferences 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, lingualj, 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- 

 scription, be little different from that of the Sepia, though less perfect. The 

 superior cei-ebral 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. 



X 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. 



3 T 2 



