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yet obtain definite conceptions of the outer world, would certainly 

 be very remarkable. 



With this fundamental difference between the ocellus and the 

 compound eye, it does not seem possible that either the ocellus 

 should be derived from the compound eye, or the compound eye 

 from the ocellus. On the contrary, both seem to point back to a 

 less developed ancestral type. Starting from such an origin, an 

 increase of the separate elements and an improvement of the 

 lens would lead to the ocellus, while 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 Limidus, according to Grenadier, is 

 formed on a plan quite unlike that of other Crustacea. Again, 

 the development of the eye in Musca, to judge from Weismann's 

 observations, is very dissimilar from that of other insects. The 

 varied position of the eye in different groujps, as, for instance, in 

 Peeten, Spondylus, Euphansia, Onchidium, &c., point to the same 

 conclusion. 



The old opinion was that the compound eyes were intended 

 for distant, the ocelli for near, vision, but Claparede long ago 

 attempted to show that the reverse was the case. 



Mr. Lowne, who has contributed to the ' Philosophical Trans- 

 actions ' for 1878 an interesting memoir on the "Eyes of Insects," 

 agrees with Grenacher in leaning towards Miiller's view, which, 

 indeed, he considers to be the only theory yet advanced capable 

 of explaining the phenomenon, "when we bear in mind the 

 relation of the recipient structures of the compound eye to the 

 nerve elements beneath them." The ocelli, on the other hand, 

 he regards as incapable of producing "anything worthy the 

 name of an image," and he suspects that their function "is the 

 perception of the intensity in the direction of light rather than 

 vision." 



In opposition to Miiller's statement that no portion of the com- 

 pound eye in any of the insects he examined corresponded in the 

 direction of the axis of the facets with the eye of the opposite side, 

 Mr. Lowne states that "in most insects the field of vision in the two 

 eyes has a common portion in the peripheral region in the 

 vicinity of the mouth ; in this region the radius of curvature of 

 the cornea is very short. It is, therefore, only adapted for the 



