No. 2.] 



HISTOGENESIS OF THE RETINA. 



421 



adult retina. By means of Golgi's method he succeeded in 

 outlining large cells extending from the rods and cones to 

 the nerve fibers of the retina. There are no anastomoses 

 between the prolongations and in general their outline corre- 

 sponds with my Figs. 4, 5 and 6. In every respect they 

 correspond with the Miiller's fibers of the inner nuclear layer 

 and I shall speak of them as such. 



A day later the nuclei have all moved to the basal end of 

 the cells, leaving on the free side of the retina a zone com- 

 posed wholly of the prolongations of the spongioblasts. This 

 free zone or peripheral veil of His {Randschlcier) is not only 



Fig. 6. — Section through the eye of Amblystoma (7 mm. long) twelve days 

 before hatching. X 133 times. G, germinating cell ; S, spongioblast. 



present in the retinas of all classes of vertebrates but extends 

 throughout the central nervous system, and is in all cases on 

 the basal side of the ectoderm. Without demonstrating the 

 point absolutely the embryological evidence is that the spongi- 

 oblasts throughout the nervous system are much the same — 

 forming Muller's fibres and the retina, and Deiter's cells in the 

 brain and spinal cord. And as the evidence is gradually 

 accumulating we must admit that the prolongations of the 

 spongioblasts do not communicate directly but only come in. 



