EYES OF BLIND VERTEBRATES OF NORTH AMERICA. 63 



diameter. In most of the sections an outer layer of cells extends 

 around the anterior surface of the lens. The interior in nearly 

 every case stained as a structureless mass, but in a few sections 

 it appeared to be made up of large irregularly shaped cells with 

 small nuclei. If any fibrous cells still persist, they did not show. 

 No capsule is present. 



The Vitreous Body.- -The vitreous body (fit. cat>., Fig. 6) 

 occupies the greater part of the eye-ball and has certainly 

 undergone but little change. The aqueous cavity has entirely 

 disappeared. 



77/6' Iris. Only the uveal part of the iris remains. It is con- 

 tinuous with the pigment epithelium of the retina and has the 

 same structure. In the thickest part it measures 68 //. The 

 cells are similar to those of the pigment layer, except that their 

 radial diameter is much greater. The ciliary processes are no 

 longer present. 



The Optic Nerve. - - The optic nerve can be traced from the 

 eye, through and along the side of Harder's gland. While the 

 nerve could be traced no further on account of an incomplete 

 series of sections, there is no doubt that the connection with 

 the brain still exists. The nerve fibers enter the eye in a com- 

 pact mass, pass through the layers of the retina until they reach 

 the nerve fiber layer, where they spread out and connect with 

 the nerve cells of the ganglionic layer in the usual manner. 



THE RETINA. 



While the retina has undergone considerable change, all the 

 layers are still present (Fig. 3). It measures 78 ;* in thickness. 

 In Aiiolis about half way between the anterior and posterior 

 parts of the eye it is 179;-* in thickness. If the macula lutea is 

 still present, the preparations do not show it. 



The Pigment Layer.- -The pigment layer (i, Fig. 6) which 

 bounds the retina externally, consists of a single stratum of rec- 

 tangular cells separated by a small amount of clear intercellular 

 substance. These cells have large oval nuclei free from pigment, 

 almost transparent and with small nucleoli. At the back portion 

 of the eye where the pigment layer measures 8 it., the transverse 

 diameter of the cells is greater than the radial diameter, but 



