STUDIES IN THE RETINA. 341 



Haviiigf traced the outward movemeut of chromatin from 

 tlie innermost layer of nuclei through the retina and ulti- 

 mately into the rods, we come to the last question : is it 

 formed in situ in this innermost '' ganglionic " layer of 

 nucleij or derived from without ? lu this layer we find a 

 rich blood-supply in all the higher vertebrates, while, in the 

 Amphibia, vessels run close to it though they may not 

 actually penetrate it. But whether the "ganglionic nuclei" 

 receive chromatin from the blood circulation or not, I should 

 like to venture on a somewhat daring suggestion in favour 

 of at least part of it being derived from a source unconnected 

 with these blood-vessels. My suggestion is based upon the 

 following observations. 



The minute staining clumps or beads upon the proto- 

 mitomic threads which run down the rods receive their 

 explanation from the fact that chromatin is travelling 

 along their threads from the nuclei into the rods. Other 

 phenomena confirm this conclusion. But we occasionally 

 find similar staining clumps upon the filaments which 

 connect the ganglionic nuclei with primitive nerve-fibrils 

 (tigs. 7 and 11). In fig. 11 these beads of staining matter 

 are only seen on those portions of the fibrils which run 

 within the cytoplasm, while the portions between the cyto- 

 plasm and the nerve-strand are the usual exquisitely delicate 

 filaments devoid of any beads of staining matter. But these 

 delicate filaments are in startling contrast with the primitive 

 nerve-fibrils, which are comparatively thick and deeply 

 stained, as shown in figs. 6, 7, 8, 9, 11. What is the meaning 

 of the sudden contrast in thickness and colour? How comes 

 it that the filamentous continuations into the nuclei of thick 

 staining fibrils suddenly become exquisitely fine and perfectly 

 hyaline? I cannot refrain from suggesting (1) that in life 

 there is a stream of chromatin along each nerve-fibril ; 

 (2) that this stream would hardly be travelling from the 

 nucleus, where, according to our previous argument, it is 

 greatly needed; and (3) that the sudden action of the fixing 

 reagent causes this stream to contract partly back into the 



