TWO KINDS OF EYES. 183 
an increase of the number of eyes would bring us to 
the compound eye. 
On the other hand, it must be admitted that there 
are reasons for considering the different kinds of eyes 
to be of perfectly distinct origin. The eye of Limulus, 
according to Grenacher, is formed on a plan quite 
unlike that of other Crustacea. Again, the develop- 
ment of the eye in Musca, to judge from Weismann’s 
observations, is very dissimiliar from that of other 
insects. The varied position of the eye in different 
groups, as, for instance, in Pecten, Spondylus, 
Luphausia, Onchidium, &e., point to the same con- 
clusion. 
It seems clear that the image produced by the 
ocelli must be altogether different from the picture 
given by the compound eyes; and we may therefore 
reasonably conclude that the two organs have distinct 
functions. It used formerly to be supposed that the 
compound eyes were intended for distant, the ocelli for 
near vision. Claparéde, however, has maintained the 
opposite theory, while Mr. Lowne regards the ocelli as 
incapable of producing ‘ anything worthy the name of 
an image,’ and suspects that their function ‘is the 
perception of the intensity in the direction of light, 
rather than vision.” 
The ocelli, or simple eyes, probably see in the same 
manner as ours do. That is to say, the lens throws an 
image on the back of the eye, which we call the retina. 
In that case they would see everything really reversed, 
