Behind the horny covering, or cornea, which consists of two plano-convex lenses, is a layer of dark pigment, which gives the characteristic colour to these eyes. This is pointed like the neck of a vase, and serves the purpose of the iris in the higher animals. This is traversed by a minute aperture or pupil, through which the rays pass by a longer conical lens to the optic nerve. A vertical section shows that each ocellus (or _little eye_) is the frustum of a pyramid, the large end or base of which is bounded by the cornea, while the other and pointed end terminates against an expansion of the optic nerve. The eminent physiologist, Dr. W. B. Carpenter, says, in describing the minute structure of these organs: "The interior of this pyramid is occupied by a transparent substance, which represents the vitreous humour (of the eyes of vertebrates), and the pyramids are separated from each other by a layer of dark pigment, which completely incloses them, save at the pupillary apertures, and also at a corresponding set of apertures at their smaller ends, where the pigment is perforated by the fibres of the optic nerve, of which one proceeds to each separate eye. [Illustration: Fig. 26.--Facets of Eye of a Bee.] "Each facet, or 'corneule' of the common cornea, is convex on both its surfaces, and thus acts as a lens, the focus of which has been ascertained, by experiment, to be equivalent to the length of the transparent pyramid behind it; so that the image produced by the lens will fall upon the extremity of the filament of the optic nerve, which passes to its truncated end. The rays which have passed through the several 'corneules' are prevented from mixing with each other by means of the layer of black pigment which surrounds each cone; and thus, no rays, except those which correspond with the axis of the cone, can reach the fibres of the optic nerve. Hence it is evident that each separate eye must have an extremely limited range of vision, being adapted to receive but a very small pencil of rays proceeding from a single point in any object; and as these eyes are immovable, they would afford but very imperfect information of the position of surrounding objects, were it not for their enormous multiplication, by which a separate eye, so to speak, is provided for each point to be viewed. No two of these, save those upon the opposite sides of the head, which are directed exactly forwards, can form an image of the same point at the same time; but the combined action of all of them may give to the insect, it may be imagined, as distinct a picture as that we obtain by a very different organisation." We venture to suggest that another reason for the vast multiplication of the numbers of "ocelli" is to enable the insects to see in what would be to us darkness. Nearly all the operations carried on in the interior of the hives are done, during the day-time, in very dim light; and in the night-time,