306 JAMES ROLLIN SLONAKER 



The pigment layer is reduced somewhat in thickness and the 

 granules are confined within the cell bodies, showing no tendency 

 to migrate. 



The retina at the age of hatching, about the twelfth or thir- 

 teenth day of incubation, has greatly increased in thickness, 

 both in the axial region and at the ora serrata (tables 4 and 5). 

 The different layers have become more sharply defined and the 

 differentiation has extended farther toward the periphery. 



At this age is noticed for the first time the early beginning 

 of the fovea centraUs. This is not any special modification of 

 the retina itself, but a thickening of the chorioid coat, caused 

 by an increase in the blood-vessels in this region. A more 

 complete discussion of the development of the fovea will be given 

 under a separate heading. 



The modification into the pars ciliaris retinae is more pro- 

 nounced and lengthened. The pigment layer and a thin portion 

 of the retinal layer have pushed farther forw^ard over the front 

 of the lens, forming the posterior part of the developing iris 

 (figs. 41 and 42). This is described in detail in deahng with the 

 development of the cornea, iris, and aqueous chamber. The 

 ora serrata is now 0.748 mm. from the lens. 



The ganglion-cell layer in the axial region is now two to three 

 cells deep. Some processes extend from these cells into the 

 nerve-fiber layer. These are the nerve fibers which also extend 

 along the nerve-fiber layer. A few can also be demonstrated 

 in the optic nerve, but the bulk of the nerve is still composed 

 of numerous elongated, spindle-like cells, characteristic of the 

 earlier ages. 



Light, faintly stained, radial bodies occur in the rod-and- 

 cone layer. They are not closely arranged and are of various 

 lengths. Many of these developing rods and cones reach almost 

 to the pigment layer. There is no migration of the pigment 

 granules toward these processes. 



Two days after hatching the retinal layers are rather sharply 

 defined throughout the whole extent of the retina (figs. 82, 83, 

 and 84). In the axial region there is a general increase in the 

 total thickness of the retina. The layers which show a notice- 



