Slonaker, Eye of the Mole. 353 



nucleus and every cell which leads to the concentric fiber for- 

 mation. It is just the beginning of the nuclear formation, to 

 which the first fibers are grouped. The cells are bent round, 

 concave toward the middle. The cells extend in two opposite 

 directions toward the front and back. In this state of develop- 

 ment the frog lens shows a later development. The mole lens 

 does not follow this proceedure. In its complete freedom in 

 the position of the cells there is also a great increase and flat- 

 tening of the cells." In regard to the capability of the lens of 

 Talpa europaea functioning as a normal lens Ritter says, "The 

 concentric structure is lacking and there can exist no mathe- 

 matical picture. The lens is transparent and allows the light 

 to penetrate to the retina. The perception of light and dark 

 could take place at the retina. The image of an object must 

 consist of distorted lines and a knowledge of the object does 

 not seem possible." 



The choroid and pigment layers of the adult eye present 

 the same general characteristics as described in the young. 

 These two layers are so closely attached and so densely pig- 

 mented that it is almost impossible to determine the boundary 

 of each. In specimens where it is possible to distinguish the 

 boundary between the choroid and pigment layers the choroid 

 has an average thickness of .0041 mm. and the pigment layer 

 of .0251 mm. They have a combined average thickness of 

 .0298 mm. This thickness is nearly uniform throughout their 

 extent. In cross sections of the eye these layers are seen to 

 run forward to the outer margin of the lens where they termi- 

 nate abruptly (Figs. 13 and 14). A small portion which 

 usually does not possess pigment is sometimes found projecting 

 forward slightly over the front of the lens. This portion cor- 

 responds to the iris. Figure 13, i shows the most perfect 

 development of the iris which I have found. One readily per- 

 ceives that the size of the pupil is about the same as the equa- 

 torial diameter of the lens. One can see the processes of the 

 pigment cells projecting into the rod and cone layer. These 

 processes are more easily demonstrated in regions where the 

 retincf has .separated from the pigment layer (Fig. 15). 



