176 ON THE FUNCTION OF OCELLI. 



Johannes Miiller considered that the power of vision 

 of ocelli "is probably confined to the perception of 

 very near objects. This may be inferred partly from 

 their existing principally in larvae and apterous insects, 

 and partly from several observations which I have 

 made relative to the position of these simple eyes. In 

 the genus Empusa the head is so prolonged over the 

 middle inferior eye that, in the locomotion of the 

 animal, the nearest objects can only come within tlie 

 range. In the Locusfa cornuta, also, the same eye lies 

 beneath the prolongation of the head. ... In the 

 Orthoptera generally, also, the simple eyes are, in 

 consequence of the depressed position of the head, 

 directed downwards towards the surface upon which 

 the insects are moving." 



From these facts, he considers himself justified in 

 concluding that the simple eyes of insects are intended 

 principally for myopic vision. The simple eyes bear 

 a similar relation to the compound eyes, as the palpi 

 to the antennae. Both the antennae and compound 

 eyes are absent in the larvae of insects." * 



Lowne observes t that " the great convexity of the 

 lens in the ocellus of Eristalis must give it a very 

 short focus, and it is manifestly but ill adapted for 

 the formation of a picture. The comparatively small 

 number of rods must further render the production 

 of anything like a perfect picture, even of very near 

 objects, useless for purposes of vision. I strongly 

 suspect that the function of the ocelli is the perception 

 of the intensity and the direction of light rather than 

 of vision in the ordinary acceptation of the term." 



* " Physiology of the Senses," translated by Baly. 



t "On the Modification of the Eyes of Insects," Phil. Trans., 1878. 



