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, when work is by no means intermitted, there would, to our eyes, be absolute darkness. To the bees, however, the scanty rays received by so many sensitive points may be sufficient to enable them to see with considerable clearness. If the simple enlargement of a single pupil, such as takes place in us on emerging from a strong into a dim light, makes so great a difference in our power of vision a fact with which we are all familiar on going from a well-lighted room into what seems for the first few seconds complete darkness we may well believe that the permanent means of entry into the sensorium of an immense number of separate rays may give greatly enlarged powers of seeing scantily illuminated objects.

Still, an opposite view is held by many naturalists, for it seems very doubtful whether there is any power in the bee of focusing these eyes, so as to adapt their range to different distances. The probability is that no such faculty of adjustment exists in them. We should expect this from the structure of the visual apparatus. Yet it seems possible that the compound eyes act as telescopes, and serve for great range of vision, but not for near objects. For, while bees dart homewards from far-off fields with the directness of an arrow, they will frequently fly against persons or things in the direct line of their course, without apparently having seen them at a little distance off. Moreover, when they have alighted within an inch or two of the entrance to their hives, they often fail to perceive its position, and constantly wander to one side or the other, searching for their way in. We might conclude, therefore, that these compound eyes confer distinctness of vision afar, and possibly ability to use up scanty light, rather than any great discernment of objects near at hand.

In addition to these "facetted" eyes, bees have, on the top of the head, three simple ones, called by some writers "coronets," by others "stemmata." Their position and arrangement are shown at g in [Fig. 27, p. 98]. The focal length of their lens is said to be short, and they are supplied with numerous filaments from the optic ganglia. The special purpose of these simple organs is not well ascertained. If their focal length is short, this would seem to imply that their range of vision is also very limited. But it is very possible they may possess a focusing power, which would adapt them for seeing at all distances. Réaumur thinks they may, with their hemispherical lens, act as microscopes. This point needs further investigation, as the subject of the uses of these two kinds of visual apparatus is, at present, very far from satisfactorily elucidated. One remarkable fact relating to the "stemmata" must be mentioned. It is that, if they be covered with a little opaque paint, the bee, on being let go, will fly continually upwards. Dr. W. B. Carpenter considers this curious fact due to automatic movements initiated by the ganglia connected with flight, uncontrolled by the visual impressions which the simple eyes convey in their natural condition. Neither kind of eye has a lid, but both are protected from dust by numerous small hairs growing round them, and in the points of junction of the facets.

How far the eyes of bees enable them to distinguish colours is still a moot point. On a priori grounds we should expect that one very definite object in the hues of flowers is to attract the notice of insects, just as we have strong reason to believe that odours exhaled in the vegetable world serve this purpose. Sir John Lubbock has detailed a series of experiments on this point, the following summary of which is abstracted from his work on Ants, Bees, and Wasps. He says, p. 304: "In recording the results I marked down successively the order in which the bee went to the different-coloured glasses (on which honey was placed). For instance, in the first journey from the nest, as recorded below, the bee lit first on the blue, which accordingly I marked I; when the blue was removed, she flew about a little, and then lit on the white; when the white was removed she settled on the green; and so on successively on the orange, yellow, plain, and red. I repeated the experiment a hundred times, using two different hives one in Kent, and one in Middlesex and spreading the observations over some time, so as to experiment with different bees, and under varied circumstances. Adding the numbers together, it, of course, follows that the greater the preference shown for each colour, the lower will be the number standing against it.

"The following table gives the first day's observations in extenso:—

Journeys.Blue.Green.Plain
Glass.		Orange.Red.White.Yellow.
11364725
25476123
31476532
42467513
51472653
61236547
72147356
83462751
95174632
101675324
114652731
26396551553537

"In the next series of experiments the bees had been trained for three weeks to come to a particular spot on a large lawn, by placing from time to time honey on a piece of plain glass. This naturally gave the plain glass an advantage; nevertheless, as will be seen, the blue still retained its pre-eminence. It seems hardly necessary to give the observations in detail. The following table shows the general result:—

Series.No. of
Exp.		Blue.Green.Orange.Plain.Red. White.Yellow.
1st.1126395165553537
2nd.May301538575972665870
3rd.July21644768273535367
4th."41543616480665056
5th."51036473940403642
6th."62289101467
7th."201133395047494149
8th."231031464852373531
9th."251022543852333546
100275427440491413349405