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[Vol. VIII. 



towards the periphery and is gradually lost. It is lost as soon 

 as it has once overstepped the border of the optic stem or point 

 of the future optic nerve. Up to the present the layer of 

 tapetum contains no pigment, but now the condition of things is 

 reversed; the retina contains pigment only at its periphery, 

 and the tapetum is pigmented all around as indicated in Fig. 7. 

 Following this stage closely it is quite easy to find the origin 

 ■of the first optic nerve fibers. Using the lens and inner 

 granular layer as guides, we locate the beginning of the optic 

 nerve in a stage between the first growth of the lens fibers, 

 and just before the formation of the inner granular layer. 



Up to the present I have been able to find some two dozen 

 specimens in which the ootic nerve is already partly formed, 



Fig. 9. — Reconstruction of the eye of Amblystoma just after hatching. X 100 

 times. X, inner granular layer. 



but communicates only with the retina and not with the brain. 

 In its growth from the retina the nerve has not yet reached the 

 brain. Fig. 8 is from a specimen in which eight or nine bundles 

 of two to three fibers each form the beginning of the optic nerve. 

 These bundles arise from about two dozen cells, all of which 

 are located in what is to be the future ganglion-cell layer of 

 the retina. The first ganglionic cell always grows toward the 

 optic stalk, as indicated in the figure. At the point of union, 

 between the optic stalk and retina, there is always a triangular 

 space, and frequently the optic nerve grows through this. 

 Along the growth of the nerve the cells are spindle shaped, 

 and as it passes through the triangular space these cells sur- 



