300 JAMES ROLLIN SLONAKER 



the granules are distributed rather unformly throughout the 

 cells. From this region back over the main portion of the retina 

 the granules are either at the outer ends or along the sides of the 

 pigment cells. Pigmentation is more dense and conspicuous in 

 the cells near the lens than in the other regions of this layer. 



The retinal layer shows a further differentiation of its cells 

 in regard to location and form. A number of large, well-stained 

 nuclei in the axial region, close to the pigment layer, are arranged 

 in a row one cell deep. The cells are not always continuous, as 

 they often have wide gaps intervening between them. This 

 row of cells can be traced well forward, almost to the equator 

 of the eye, where it blends with the main mass of nuclei. This 

 is evidently the beginning of the outer nuclear layer which will 

 later form the rods and cones (KolHker, '83; Babuchin, '63; 

 Max Schu^tze, 66; W. TNIiiller, '74). 



In the axial region another row of well-stained nuclei lies at 

 the inner edge of the retina. This row is one cell deep and shows 

 frequent wide spaces between the cells. A slight indication of 

 nerve fibers is seen in this region. Toward the periphery of the 

 retina this row of cells becomes less and less conspicuous until 

 it disappears by blending with the main mass. This is the early 

 differentiation of the ganglion cell laj^er. These two layers of 

 cells are being formed by cells migrating from the main mass 

 of cells. 



Separating these two single-celled layers from the main mass 

 of nuclei are two indefinite band-like regions with few nuclei. 

 These are destined to become the inner and outer molecular 

 layers. These two layers become indistinct and disappear 

 toward the equator as the nuclear laj^ers blend with the main 

 mass of cells. At all points they show cells migrating inward 

 and outward to form the ganglion cell and outer nuclear layers. 

 The main mass of cells from which the above cells have migrated 

 will become the inner nuclear layer. 



Although this early differentiation can be made out by careful 

 manipulation of the microscope, it is still too indistinct to show 

 in the microphotographs (figs. 53 and 54). 



