68 H. M. BERNARD. 



single one were absent, a blind spot would ensue as a neces- 

 sary consequence. 



The results here published, obtained solely by comparisons 

 not only of different eyes but of the same eye at different 

 ages, involve a direct contradiction to this interpretation of 

 the phenomena. If there ever were distinct cells com- 

 posing the retina, their walls were early lost.^ The func- 

 tional retina is a continuous cytoplasmic reticulum 

 in which nuclei are suspended, and the nuclei are 

 not stationary. (1) A large proportion of those which are 

 present in the young retina move outwards when it begins 

 to function to become the nuclei of the new rods required by 

 growth. (2) Their places are supplied by others migrating 

 inwards from the rim. (8) The outward movement continues 

 as long as life lasts, for in old eyes the nuclei of both the 

 innermost and the middle nuclear layers are found to have 

 largely disappeared. Whether 3 is for the supply of 

 new rods or for some regenerative process we have no 

 means yet of deciding. These migrations, and especially 

 this using up of the nuclei, in a retina which is all the while 

 functioning normally, shows clearly that some other value 

 must be assigned to its structural elements than that which 

 is needed by the neuron theory as applied to this organ. It 

 is clear that these nuclei are not the nuclei of cells taking 

 part in fixed morphological chains, every link of which 

 is essential. The nearest approach we obtain to anything 

 like a permanent cell in the retina is the rod with its nucleus; 

 that it would be inaccurate to persist in using the term 

 "visual cell" in this connection will be conclusively shown 

 in my next paper. 



With reference to the retina itself as the specific organ of 

 vision, by far the most important result obtained is the 

 discovery of some new details relating to the origin and 

 structure of the rods, that is of those structures which are 

 peculiar to the retina as the visual organ. According to the 



' Wliiit appears to be I lie <,Ma(lual dissoliiUon of cell walls may often bo 

 seen where Uie jouiig retina is passing into I he cells of the iris. 



