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MALL. 



nuclear layer are rod-and-conc bearing cells, and we can not 

 admit that when they multiply that they can return to their 

 embryonic type and regenerate all the retina structures. They 

 must produce their kind only, i.e., form rods and cones. 



The above discussion shows us clearly, I think, that the 

 histogenesis of the retina is after the plan of histogenesis of 

 nerve tissue in general. The original growing point is on the 

 side which was the outer border of the ectoderm. This state- 

 ment applies to the central nervous system as well as the sense 



organs. 



The optic nerve arises in great part from the dorsal end of the 

 ganglion cells and grows into the brain. In general we can 

 view nerve cells as having receiving and transmitting ends. 

 The receiving end is the side which was directed originally 

 towards the outside of the body. In the retina the receiving 

 end is most highly modified in the rods and cones ; the trans- 

 mitting end in the ganglion cells ; and an intermediate stage 

 with both equally modified in the bipolar cells of the inner 

 nuclear layer. 



After the retina is fully formed just behind the lens, its 

 further growth is by addition to the periphery. This secondary 

 growth is a continuation of the primary and is in no way a 

 modification of it. 



The University of Chicago, 

 Feb. 24, 1893 



