174 ANDREWS. [Vol. VII. 



the end near the rod, but extending in some cells and in some 

 eyes a very variable distance out towards the nucleus. The 

 two kinds of pigment retain their natural colors, except that the 

 blue granules tend to turn red in sulphuric acid macerations. 



When properly stained, a large nucleus is found in the periphe- 

 ral end of each cell (Fig. 14) near the cell process. These 

 processes are nerve fibres and can be traced for some distance 

 in a large nerve, the optic nerve, passing from the retina to the 

 brain. 



All the retinal cells are essentially alike : the swollen vacuo- 

 lated form seen in Fig. 14, a, is common in poorly preserved 

 sections as well as in some macerations, but is to be regarded as 

 an artificially changed cell. 



The layer of retinal rods forms a clear refracting lining to the 

 pigmented part of the retina (Fig. 8), and is sharply defined on 

 one side by the dense pigment zone, while on the central aspect 

 it is but dimly 1 marked off from the clear central mass that I 

 shall speak of as the lens. These rods are short near the pupil 

 and largest at the bottom of the optic cup opposite the pupil. 

 They are not all straight, but variously bent to fit into the 

 curved space they occupy. In macerations they readily break 

 off from the retinal cells and appear as clear rods in side view 

 or as polygonal masses in end view (Fig. 12). Their actual con- 

 tinuity with the retinal cells may, however, be made out in some 

 preparations (Fig. 9), each being partly abstricted from the end 

 of the cell by the groove full of dark pigment surrounding the 

 clear axial stalk. This is evident also in radial sections (Figs. 

 22, 23) where each rod is a continuation of a cell. Moreover, 

 each rod has a granular axial part continued by the slender 

 stalk of the rod into the granular, yellow, axial part of the cell, 

 and a clearer superficial part or cell wall continuous with the 

 part of the cell containing blue pigment. 



Tangential sections of the rods near the pigment zone (Fig. 

 24) show the granular axes as rounded areas imbedded in a clear 

 matrix, in which polygonal cell boundaries about each axis may 

 also be brought out (Fig. 25). 



In other stains the axes may appear light in a dark homoge- 

 neous matrix. 



The axes are thick near the pigment zone, but diminish so 



1 The distinctness of this boundary is exaggerated in Fig. 8. 



