No. 383.] BASIS FOR A THEORY OF COLOR VISION. 855 
But what is the disposition of the impulses after leaving the 
retina? They, of course, follow the optic nerve fibres to the 
optic ganglion and pass from there to the cerebral hemispheres. 
But why should we have these two internal centres? The con- 
ditions in Acilius furnish a partial answer, I believe, to the 
question. In the larvæ of this insect there are six pairs of 
ocelli, and each ocellus happens to have a characteristic size, 
shape, and arrangement of retinal cells. The nerves to the 
ocelli unite to form a common nerve, which near the optic 
ganglion again separates into six nerves, each one ending in a 
distinct mass of fibrillated substance. These masses of “ Punct- 
Substanz” present such a striking resemblance in relative posi- 
tion, size, form, and structural details to the corresponding 
retinas that there cannot be the slightest doubt as to which 
ocellus each medullary core belongs. It is not claimed that 
there is absolute agreement between the retina and its mass 
of Punct-Substanz, but the resemblance goes so far that 
the singular appendage to retina I, the median furrows in 
retinas I to V, and the absence of this furrow in the circular 
retina of ocellus VI, together with the presence of a peculiar 
patch of inverted cells, are all represented in the corresponding 
part of the optic ganglion by some change in the number or 
arrangement of the fibrils. This is a fact of fundamental 
importance, and while it has been observed only in this instance 
where the conditions are especially favorable, the principle 
probably holds good for other animals as well. This similarity 
between the inner and outer extremities of the visual apparatus 
indicates that the Pumnct-Sudbstanz of the optic ganglia con- 
sists of a series of fibrils which in their numbers and general 
arrangement agree with the retinidial fibrils to which they are 
united ; and it also indicates that a series of changes initiated 
by light in the retina are re-presented in the optic ganglion by 
another sequence of changes having time and spacial relations 
similar to those in the retina. The whole apparatus is com- 
parable with a telephone, or with a Marconi transmitter and 
receiver. As the structure of such end organs must be to a 
certain extent created by the ether waves that rouse them to 
activity, so the structure and adjustments in the optic ganglion 
