STUDIES TN THE RETINA. 385 



vital phenomena; and lastly, its startling movements during 

 cell division, have forced the more passive cytoplasm into 

 the background. It has even been somewhat prematurely 

 called '■ the hereditary " substance. 



What the relations are in their entirety between this 

 important substance and the protomitomic system remain 

 still to be discovered, but we are able here to describe 

 certain suggestive phenomena. The bare description of the 

 structure of the latter system would have been sufficient to 

 guarantee its fundamental importance for the proper under- 

 standing of organic life, did we not know at the same time 

 that its threads are the paths along which the nerve-stimuli 

 tivavel. Such a system clearly rivals the claim of the chro- 

 matin to the first place, and their mutual relations become 

 a matter of supreme interest. 



The most important result arrived at is that the chro- 

 matin, like the granular cytoplasm, is an unstable 

 quantity in the retina, in that it also streams outward towards 

 the rod-layei". Unlike the granular cytoplasm, which seems to 

 travel freely among the strands of the syncytium (although the 

 exact nature of the movements have still to be made out), 

 the chromatin only travels along the protomi- 

 tomic filaments. Its morphological value, therefore, like 

 that of the cytoplasm, is small, depending solely upon the 

 fact that it tends to accumulate within the nuclear nodes and 

 in varying forms and quantities. 



The evidence for the streaming of the chromatin from 

 nucleus to nucleus is of two kinds, direct and indirect. 



The direct evidence is not abundant, but, taken together 

 with the indirect, it is very significant. As already described, 

 the protomitomic filaments, as they run from nucleus to 

 nucleus, are usually made visible when coated or beaded 

 with staining matter. In young, developing rods, continuous 

 streams of such matter can sometimes be seen (Part II, figs. 

 15 a, 27 c and d) ; at other times a string of beads (see Part II, 

 figs. 3 a, 27 h). In fig. 18 c of this paper, the staining 

 matter is irregularly clotted on the connecting filaments, 



