'ni the Eye of ' the Sepia Loligo. 195 



is altogether peculiar. It is well known, that shortly after 

 the optic nerve has escaped from the cartilaginous cranium of 

 the cuttle-fish, it expands into a ganglion or medullary mass 

 of great magnitude, much exceeding the brain in size. This 

 ganglion divides as it were into two before reaching the pos- 

 terior part of the sclerotic, and from each of these two masses 

 of nervous matter arises a set of nerves, which, penetrating the 

 sclerotic, pass into the eye-ball to form, or at least to be 

 connected with, the retina. At the point where they pene- 

 trate the eye-ball, they cross each other very distinctly. The 

 reason of this is apparent on laying open the eye-ball, for we 

 then find that the retina is a double membrane, the interior 

 being of a brown colour, (probably from a very thin mem- 

 brane expanded over the inner surface,) and the exterior of a 

 white, opaque, medullary structure. The retina thus formed 

 covers a great portion of the inner surface of the sclerotic. 

 Anteriorly, i. e. a few lines behind the fixed or equatorial 

 margin of the lens, it seems to terminate in a very fine radiat- 

 ed circle, composed of .innumerable straight and parallel 

 fibres, which have been compared not inaptly to the ciliary 

 processes of vertebral animals, and are inserted into the fis- 

 sure, dividing the lens into two hemispheres. The view, 

 however, I have adopted of these fibres, is somewhat differ- 

 ent ; they have appeared to me constantly to arise from the 

 sclerotic, but to be intimately connected with one of the lay- 

 ers or membranes of which the retina is composed. At a 

 short distance, behind the margin of the lens alluded to, I 

 have found, in the larger specimen examined, viz. the Sepia lo- 

 ligo, that the white, opaque, medullary portion of the retina 

 seems to cease, and, at this point, the whole membrane is 

 firmly attached all round the eye-ball to the sclerotic. The 

 brownish coloured membrane is continued forward to unite 

 very firmly with the ciliary fibres ; to form, as it were, a part 

 of them, and to accompany them as far as the crystalline hu- 

 mour. 



It was now an object of considerable interest to ascertain 

 the precise nature of the terminating edge of the white, opaque, 

 and external layer of the retina. The specimen I examined 

 did not permit of the investigation to the extent I could have 



