54 THE AMERICAN MONTHLY [Apr. 



whicli lias a single layer of transparent pavement epithe- 

 lium on the surface. 



The shape of the interior of the eye which includes the 

 organs of vision is nearly oval. It is longer in the equa- 

 torial than in the polar diameter, measuring 1-40 by 1-50 

 of an inch and it is surrounded by a choroid coat which 

 becomes continuous with the cornea. On polar section 

 the interior of the eye is seen to be divided into two 

 nearly equal parts by a beautifully curved line formed 

 by the expansion of the optic nerve. Fig. I, e. 



The anterior portion or chamber contains nothing but 

 the lens which occupies nearly the whole of it. The pos- 

 terior chamber contains the complex structure of the 

 retina, tapetum and pigment and all these collectively 

 are situated in the end of a tentacular portion of the 

 mantle. I shall now give the details of the several parts 

 separately as the result of my observation. 



The Cornea. — The tissues of the cornea are arranged 

 in two layers ; an outer pavement epithelium and an 

 inner or true fibrous layer of the cornea. The membrane 

 of Descemet and the internal epithelium or endothelium, 

 are wanting. The cornea simply resting upon the lens 

 without the intervention of aqueous humor. In shape it 

 is circular and at the periphery or margin it is continuous 

 with the choroid coat and tentacular portion of the eye. 



It measures 1-80 inch in diameter. (These measure- 

 ments are for average eyes). The external or outer 

 layer consists of a single layer of nucleated pavement 

 epithelial cells elongated in a direction perpendicular to 

 the surface and situated directly upon the corneal tissue. 

 In a stained section it appears like a row of beaded cells 

 ^s a margin to the cornea. The cornea seems to be made 

 up of a fibrous structure with very fine conmmunicating 

 channels which may be seen upon cross-section of eyes 

 treated with Osmic Acid also by gently scraping the 

 epithelium from the surface and impregnating with Grold 



