1884.] NATURAL SCIENCES OF PHILADELPHIA. .305 



the lens. The anterior chamber is divided from the posterior by 

 the iris, the latter being a flattened projection of the vascular 

 layer of the chordidea. The hole in its centre is called the pupil. 

 These two chambers are filled with a fluid called the humor 

 aqueus. Back of the lens and iris is the largest chamber of the 

 eye-ball, called the vitreous chamber, and contains a semi-fluid 

 mass, known as the corpus vitreum. 



The lens is a cellular body, suspended from the process ciliaris 

 by the suspensory ligament; the process ciliaris of the iris, is an 

 extension of the vascular layer. 



The retina is composed of many layers ; one of the most 

 external, that which is directed toward the chordidea, is called the 

 laj'er of the rods and cones. The innermost layer, that next to 

 the corpus vitreum, is the layer of fibres of 

 the optic nerve ; between these two are several 

 ganglionic layers. The whole retina is practi- 

 cally transparent, and the light passes through 

 it unchanged to the point of contact of the 

 rods and cones with the pigmented layer. Here 

 the light-motion is transferred into a " nerve- 

 energy," which is transmitted to the perceptive 

 centres of the brain, ^ no light-motion, of course, 

 passes beyond the receiving sensory fibres 

 internally. The optic nerve pierces the retina fig 3'— Diagram rep- 

 a little on the nasal side of the optic axis. of'S T inTbl 

 It will thus be seen that the extraneous color- and ''" nenl^ne^r^ " 

 waves have, in their impinging upon the sen- the°bfiln,%' 'f "cier" 

 sory tips of the rods and cones, passed through ?eunl ; VS^V'; 

 the entire thickness of the retina, before it has The'r^ina o^tVJ'nervx^. 

 been put in a position to give a proper sensory ^^^''sy- 

 impression. In fig. 3, I have given a diagrammatical repre- 

 sentation. B is a. ray of light passing through the retina, and 

 impinging on the point of a rod or cone, n representing the 

 return through the cells of the retina (r) to the nerve-fibres, and 

 then passing by them to the brain, B. 



Now, to consider the development of the eye, we find that in 



' For a detailed account of this, see the forthcoming paper of Oliver, 

 Charles A., "A Correlation Theory of Color Perception," Amer. Jour. 

 Med. Sci., Jan., 1885. Dr. Oliver has kindly allowed me access to the 

 manuscript of this article. 



R 



