Stonry— Limitation of Insect Vision. 233 
the objects of the world around us exactly as we now do. For 
the direct physical adjunct of a visual perception in our mind of a 
point of the object is not any event in the eye or along the optic 
nerve, but in a more deep-seated part of the brain, probably in its 
occipital lobes which lie in the back of the head, over the cere- 
bellum. Now [speaking from the physical standpoint] the way in 
which this event in the occipital lobe is usually evoked is by light 
from the point of the object being guided through the eye to one 
of the rods or cones, after which some event travels along one of 
those nervelets with attendant nerve-cells which penetrate the retinal 
layer from the expansion of the optic nerve, and each of which 
is associated with one individual rod or cone. This is succeeded 
by some event along one fibril of the optic nerve, after which 
there seem to follow other events within the brain, which finally 
lead up to that particular event which, and which alone, is the 
true physical adjunct of the visual perception in our mind—our 
perception of that point of the object from which the light set out 
to enter the eye. I, for convenience, speak of this event as 
situated in the occipital lobe, although its location can hardly be 
_ said to be ascertained. 
Now it is evident that the image on the retina is only one 
link in this long chain of physical causes and effects, and that the 
image might be erect as it is in the compound eyes of insects, or 
inverted as in our eyes, or might have any other orientation, and 
that nevertheless the positions of the rod or cone, nervelet, fibril of 
optic nerve, etc., could be so disposed as to produce precisely the 
same final event within the occipital lobe of the brain as now 
occurs. Now it is this last alone which is essential, the others 
being only instrumental in bringing it about: it alone is the true 
physical adjunct of the visual perception which becomes part of 
the mind. 
Again, although the train of causes and effects described above 
are the usual process by which this adjunct of perception is 
evoked, it is not by any means the only way in which it can be 
brought about, as is conspicuously manifested by dreams, and 
may be detected by a careful introspective study of the memory 
of visual perceptions. I am of opinion that in all cases when 
remembering a past scene there is some dim, usually a very dim, 
recurrence of the perception, or of parts of it: at all events, under 
