﻿AMPHISB^NA. 



45 



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 of the 

 layers are still present (fig. 15 a). It measures 78 ju. in thickness. In Anolis 

 about half-way between the anterior and posterior parts of the eye it is 179 /a 

 in thickness. If the macula lutea is still present, the preparations do not show it. 



The Pigment Layer. — The pigment layer (i, fig. 14), which bounds the retina 

 externally, consists of a single stratum of rectangular 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 part of 

 the eye, where the pigment layer measures 8 ju,, the transverse diameter of the cells 



Fig. 



(a) Horizontal Seclion of Retina of Amphisbmna putKlata, showing Different Layers. 

 (6) Horizontal Section of Retina of A iwiis. 



is greater than the radial diameter, but toward the anterior part, where the layer 

 becomes thicker, the radial diameter becomes much the greater. The greatest 

 thickness of this layer is near the lens, where it measures 68 /x. The outer surface 

 of the pigment cells — that which lies next to the choroid — is smooth and slightly 

 convex. The inner surface, on the other hand, is very irregular. The cells at this 

 place are very densely laden with pigment and prolonged into filamentous pro- 

 cesses which extend between and amongst the cones. In fact, the cones may be 

 said to be embedded in the pigment cells. This layer differs but little from that of 

 Anolis, except at the anterior part of the eye, where it becomes much thicker. 



The Cones. — No rods are present. The cones (2, fig. 15 a) consist of an upper 

 and a basal part. The basal part is elliptical in shape and stains uniformly through- 



