166 EYE OF THE NAUTILUS. 



will enable the reader to understand this description : 

 much, however, remains to be ascertained. 



According to Professor Owen, the eye of the nautilus 

 is far more simple, the light being admitted through an 

 anterior transparent membrane into a chamber lined 

 with black pigment, which covers a nervous expansion 

 of the optic ganglion, and has an anterior or pre-pig- 

 mental retina, as in the octopus ; but no crystalline lens 

 has been found. Excepting in the nautilus, (Na^ttilus 

 pompilius,) all the cephalopods appear to be endowed 

 with organs of hearing ; but these organs, the first steps, 

 as it were, to the complex auditory apparatus of birds 

 and mammalia, are in their lowest condition — in their 

 simplest structure. In the anterior part of the carti- 

 laginous cranion are two separate cavities, and in each 

 of these is a membraneous vesicle, of a rounded or some- 

 what oval figure, suspended by means of numerous mi- 

 nute filaments, regarded by some anatomists as vessels ; 

 over the vesicle, delicate branches of an auditory nerve 

 ramify. Internally, the vesicle contains a gelatinous 

 fluid ; and, externally to its posterior part, a small cal- 

 careous body is attached. Such is the ear of the cepha- 

 lopods, an organ useless for the appreciation of the vi- 

 brations of the air, but no doubt qualified for receiving 

 or being affected by the oscillations of the aqueous 



