854 THE AMERICAN NATURALIST.  [Vou. XXXII. 
complicate the processes going on within the retina, but rather to 
simplify them, in that they make it possible for the fibrils of the 
same length in many adjacent rods or cones to deliver their 
impulses into gradually converging channels. 
Many questions arise in this connection that it is as yet 
hardly profitable to discuss, as, for example : How large an 
area of rods and cones is tributary to a single optic nerve 
fibre? Are these areas distinct or do they overlap each other? 
And, further, to what extent is there a qualitative analysis of 
impulses previous to convergence; that is, are all the sensa- 
tions initiated in the long red fibrils of, say, three hundred 
cones transmitted by a single axis cylinder of the optic, nerve, 
and if something of this kind takes place, is it true only for the 
red, green, and blue sensations or for ten, or twenty, or more 
different sensations? But whatever the answer to these ques- 
tions may be, that there must be, on any theory, some kind of 
convergence of impulses from the rods and cones towards the 
optic nerve, is decisively demonstrated by the numerical rela- 
tions between the rods and cones in the ganglionic cells and 
the fibres of the optic nerve. 
Certain facts appear to indicate that there is a qualitative 
as well as a quantitative convergence. It is well known, for 
example, that the stimulation of an area as small as the base of 
a single cone may produce the sensation of light, but that a con- 
siderably larger area must be stimulated before the sensation 
of any distinct color is produced. This fact is apparently cor- 
related with the distribution of the large ganglion cells of the 
inner layer, because these cells are more numerous around the 
fovea than on the periphery of the retina, indicating that there 
should be less convergence of impulses there than at the outer 
margin, where one ganglion cell of the inner layer must collect 
the impulses from a very large number of rods and cones. 
This appears to be the case, for we can distinguish the colors of 
small objects better with the centre of the retina than with the 
periphery ; or, rather, small objects which barely produce the nen 
sation of a distinct color when seen with the centre of the retina 
must be considerably increased in size in order to produce this 
effect when seen with the periphery. 
