428 JAMES ROLLIN SLONAKER 



and cones (fig. 37, A). Near the cell bodies these pigment 

 granules are closely grouped together and form a closely com- 

 pacted mass (fig. 37, c-c A, and C). Farther inward this mass 

 divides into from six to nine bundles of closely arranged granules 

 (d-d A, and D). As this migration continues inward these 

 bundles divide into brush-like filaments which lie between and 

 largely fill the spaces between the external segments of the rods 

 and cones so as to almost completely conceal them (e-e A, and E). 



f»~«^ 





Fig. 37 Camera-lucida semidiagrammatic drawings of the pigment cells of 

 the retina of the sparrow killed in the light. A, pigment cells from a section 

 perpendicular to the retina, showing the migration of the pigment granules from 

 the cell bodies, B-B, toward the inner surface of the retina. B, Pigment cells as 

 seen in a section cut tangential to the retina or in the plane B-B, perpendicular 

 to fig. A. Few pigment granules remain at the level of the nuclei. C, drawing 

 from a tangential section of the eye in a plane perpendicular to fig. A, along the 

 line C-C. This shows the pigment granules forming almost a solid mass. D, 

 drawing from a tangential section of the eye in a plane perpendicular to fig. A, 

 along the line D-D. At this level the pigment granules are arranged in bundles. 

 E, drawing from a tangential section of the eye in a plane perpendicular to 

 fig. A, along the line E-E. The bundles of pigment granules have further divided 

 and iiow appear as minute masses which extend inward to the region of the junc- 

 tion of the inner and outer segments of the cones. X 465. 



In the retina of a bird killed in the dark the granules show 

 little migration and are grouped in a mass in the ijiner portion 

 of the cell body. The external segments of the rods and cones 

 are now easily seen. I agree with former writers that the func- 

 tion of these cells is evidently that of protecting the rods and 

 cones from excessive light. 



