On the whole, we are rather inclined to agree with Lubbock and Forel, that the ocelli are useful in dark places and for near vision. They are, as Lubbock states, especially developed in insects, such as ants, bees, and wasps, which live partly in the open light and partly in the dark recesses of nests. Moreover, the night-flying moths nearly all possess ocelli, while with one known exception (Pamphila) they are wanting in butterflies. Finally, remarks Lubbock, “Whatever the special function of ocelli may be, it seems clear that they must see in the same manner as our eyes do—that is to say, the image must be reversed. On the other hand, in the case of compound eyes, it seems probable that the vision is direct, and the difficulty of accounting for the existence in the same animal of two such different kinds of eyes is certainly enhanced by the fact that, as it would seem, the image given by the medial eyes is reversed, while that of the lateral ones is direct” (p. 181). =Mode of vision by facetted eyes.=—The complexity of the facetted eyes of insects is amazing, and difficult to account for unless we accept the mosaic theory of Müller, who maintained that the distinctness of the image formed by such an eye will be greater in proportion to the number of separate cones. His famous theory is thus stated: “An image formed by several thousand separate points, of which each corresponds to a distinct field of vision in the external world, will resemble a piece of mosaic work, and a better idea cannot be conceived of the image of external objects which will be depicted on the retina of beings endowed with such organs of vision, than by comparing it with perfect work of that kind.” [Illustration: FIG. 267.—From Lubbock. ] How vision is effected by a many-facetted eye is thus explained by Lubbock: “Let a number of transparent tubes, or cones with opaque walls, be ranged side by side in front of the retina, and separated from one another by black pigment. In this case the only light which can reach the optic nerve will be that which falls on any given tube in the direction of its axis.” For instance, in Fig. 267, the light from _a_ will pass to _a′_, that from _b_ to _b′_, that from _c_ to _c′_, and so on. The light from _c_, which falls on the other tubes, will not reach the nerve, but will impinge on the sides and be absorbed by the pigment. Thus, though the light from _c_ will illuminate the whole surface of the eye, it will only affect the nerve at _c′_. According to this view those rays of light only which pass directly through the crystalline cones, or are reflected from their sides, can reach the corresponding nerve-fibres. The others fall on, and are absorbed by, the pigment which separates the different facets. Hence each cone receives light only from a very small portion of the field of vision, and the rays so received are collected into one spot of light.