No. 2.] 



HISTOGENESIS OF THE RETINA. 



423 



At this time the whole eye has advanced in its development, 

 and in its centre the complete thickness of the retina is filled 

 with cells. Cells arising from the germinal layer have moved 

 through the fine net-work of the prolongation of the spongio- 

 blasts and are now immediately behind the lens. This is 

 the third migration of nuclei. In Fig. 7 we have a retina 

 representing all of the various stages in its development. 

 In the m.iddle it is the most advanced, and at the periphery it 

 is just beginning. In fact this is what we have in all growing 



Fig. 8. — Section through the eye of Amblystoma (lo mm. long) five days before 

 hatching. X 300 times. G, germinating cell ; S, spongioblast ; N, neuroblast. 



retinas, the periphery always being the growing point. Fol- 

 lowing Fig. 7 from its center to the periphery, we find in the 

 center the whole retina filled with cells; on either side the large 

 spongioblasts completely formed ; and farther towards the peri- 

 phery the development of the spongioblasts. Viewed from the 

 lens side we have in the various stages of the development of 

 the retina, at first a central spot indicating the free ends of the 

 spongioblasts, which in the successive stages move as a zone 



