336 H. M. BERNARD. 



while in figs. 10, 11, it is again beaded on the filaments as 

 they run through the cytoplasm. The evidence shows, then, 

 that whereas one normally finds the chromatin massed in 

 and confined to the nuclei, there are times when it is found 

 travelling beyond the usual nuclear limits on to the connect- 

 insr filaments. That the chromatin can leave the nucleus 

 and wander into the cytoplasm surrounding it has long been 

 a recognised fact. The discovery of the protomitomic 

 filaments throws a new light upon this Avandering. Whether 

 there is any cytoplasm or not, the chromatin travels along 

 the protomitomic filaments. 



The most conclusive evidence that this chromatin, seen in 

 clumps and beads upon the connectiug filaments, is actually 

 travelling from nucleus to nucleus outward, is gathered from 

 a study of the whole retina. 



In very young eyes, before they have commenced to 

 function, the chromatin is fairly evenly distributed among 

 all the nuclei alike, but sooner or later this condition changes, 

 and the bulk of the chromatin is seen in the outermost nuclei. 

 Fig. 25 is from a kitten two days old ; it shows nearly all the 

 proximal nuclei as clear, almost empty vesicles, but a most 

 striking accumulation of the chromatin in the nuclei along 

 the distal edge of the retina, i.e. in the rod-nuclei. I have 

 no embryonic cats' eyes, but, judging from other embryos, 

 we may assume that this accumulation of the chromatin is 

 secondaiy. It is evidently preparatory to rod-formation. 



The first great structural change in the retina after birth is 

 the production of the rods as a compact mass of vesicles 

 protruded from its distal surface. Into each of these rods a 

 staining reticulum grows out from its nucleus, the distribution 

 of which within the rod has already been described. A 

 general migration of nuclei towards the place where new rods 

 are to be protruded can be seen, a migration which reminds 

 us of the movements of the nuclei in vegetable filaments 

 towards the spots where growth is about to take place.^ 



' See Haberlaiidt, ' Ueber die Bezieliungen zwischeii Function und Lage 

 des Zellkerns,' Fischer, 1887. 



