148 ELEMENTARY BIOLOGY. [XII. 



great number of minute square areas or facets, 

 each of which shews faint signs of furrows crossing 

 it diagonally from corner to corner. 



6. Imbed the eye and cut a number of sections from 

 it perpendicular to its surface : mount in glycerine 

 and examine with one inch objective. 



a. If the section has passed through the middle of 

 the eye it will be seen to present a central mass 

 (optic ganglion) from which a number of lines 

 appear to radiate to the facets on the surface. 

 These radiating lines (which are obscured here 

 and there by pigmented layers) are indications 

 of the striated spindles, connective rods and 

 crystalline cones. 



c. Examine your thinnest section with a high power, 

 or tease out one of your thicker ones in gly- 

 cerine. Beginning at the exterior make out suc- 

 cessively 



cc. The cornea, answering to one of the superficial 

 facets. Its flat outer and slightly convex inner 

 surface. Immediately beneath the cornea there 

 will be seen (in good specimens) a slightly 

 granular layer. 



yS. The crystalline cone, an angular transparent 

 body which is usually obscured by pigment. If 

 this is the case, another section must be mounted 

 in dilute caustic potash, which removes the 

 pigment. 



7. Behind the crystalline cone comes the con- 

 nective rod. It is widest in front where 

 it joins the cone but narrows posteriorly 

 where it is continuous with the striated 



