Stonsy—Limitation of Insect Vision. 237 
ness and colour, but not of position. Now this can manifestly be 
effected by distributing the points of an image of the object over 
an apparatus such as the layer of rods and cones, consisting of 
closely packed individuals, each of which is capable of acting on its 
own nervelet ; or through an intermediate apparatus, which con- 
sists of channels for transmitting light as numerous as the rods and 
cones, each of which conducts the light from a specific point of the 
image to its own rod or cone, which latter may, in this case, be 
situated at a distance from the place where the image is formed. 
The first of these is the arrangement which we find in our own 
eyes; the other seems to be that which we find in the compound 
eyes of insects. Now it is doubtful whether any other machinery 
for bringing about the result than one or other of these two can be 
devised. These, at all events, are the waysin which nature attains 
the end ; so that neither man or nature seem to have found out any 
other. But the position of the images, whether erect, inverted, or 
any other, is obviously immaterial. It is the ultimate effect within 
the occipital lobe of the brain that is alone essential. 
Sxcrion II1.—O/f Vision with compound Eyes. 
After these preliminary remarks on vision in general, we seem 
to be in a position to deal intelligently with the inquiry—How is 
the retinal image formed in insects? and what kind of vision do 
they enjoy through the instrumentality of the compound eyes with 
which they are furnished? These questions may be most con- 
veniently dealt with by describing a rough model of an insect’s 
eye. Imagine a hemispherical shell of some transparent material, 
e.g. half of a sixteen-inch globe of glass, that is, a globe of which 
the diameter is sixteen inches. Place your eye at its centre, and 
look through it at the objects of nature around you. Next, let an 
accurate picture of these objects be painted on the outside of the 
globe, so that when you place your eye at the centre you still see 
the same scene as before. Now let a network of scratches be 
made all over the painting, dividing it into patches, each of 
which is the size of a square quarter of an inch. This is about the 
size of the cross-section of a lead pencil. ‘There will be about 
6400 of these patches on the hemisphere. Next, let the paint of 
