CHAPTER VIII. 
ON THE SENSES OF ANTS. 
The Sense of Vision. 
Ir is, I think, generally assumed not only that the world 
really exists as we see it, but that it appears to other 
animals pretty much as it does to us. A little con- 
sideration, however, is sufficient to show that this is 
very far from being certain, or even probable. 
In the case of insects, moreover, the mode of vision 
is stillan enigma. They have, at least many of them 
have, a large compound eye on each side; and ocelli, 
generally three in number, situated on the summit of 
the head. The compound eyes consist of a number of 
facets, each situated at the summit of a tube, to the 
base of which runs a fibre of the optic nerve: 
The structure of the ocellus and that of the com- 
pound eye are essentially different, and it does not seem 
possible that either the ocellus should be derived from 
the compound eye, or the compound eye from the ocel- 
lus. On the contrary, both seem to point back tc 
a less developed ancestral type. Starting from such an 
origin, an increase of the separate elements and an im- 
provement of the lens would Jead to the ocellus, while 
