females, are considered blind. Even the males of one species (Termes fatalis) are said by Dr. König *, who observed them at Tranquebar, to have only an obscure spot near the antennæ; and he could not perceive the gold-coloured point in the forehead, described by Fabricius t. The seinsects, it mus thowever be remarked, like Latreille's blind French ants, are impatient of light, and always, even in foraging, walk under cover. If we turn to insects which are admitted by all to possess vision, we shall find that authors are by no means agreed respecting its nature and extent, as is most strikingly the case in the instance of bees. "How great," exclaims the elder Huber, "is their perfection of sight, as if to compensate the defects of their hearing. The bee, from this cause, recognises its habitation amidst an apiary of numerous others resembling it, and returns in a straight line with great velocity: we must suppose that it is distinguished by marks escaping our notice. The bee departs, and flies straight to the most flowery field; and having ascertained its course, it is seen traversing it as directly as the flight of a cannon or musket ball. When it has made its collection, it rises aloft in the air to reconnoitre its hive, and returns with the rapidity of lightning §." Wildman, on the other hand, tells us that he has observed them go up and down, seeking the door of the hive, and be obliged after alighting to rise again in order to find it. He conceived that they see better when flying than when alighted||; not, however, as Dr. Bevan remarks, because their vision is improved by the act of flying, but from objects being placed at a greater distance, and better adapted to the focus of * Beschäftigungen der Berlin, iv. 1. + Bestimmung des Geschlechts, i. 179.1 See page 73. § Huber on Bees, p. 221.1 Wildman on Bees. M their eyes*. The observations of Dr. Evans corro. borate those of Wildman. "We frequently observe bees," he says, "flying straight homeward through the trackless air, as if in full view of the hive; then running their heads against it, and seeming to feel their way to the door, with their antennæ, as if totally blind t." The experiments of Sir C. S. Mackenzie support the same doctrine, for he remarked the imperfect vision of bees, and how much they are sometimes puzzled to find their way, if the hives were removed two or three yards from the place where they usually stood; and he found that, for the first day or so, they did not venture to fly to a distance, till they had visited and recognised neighbouring objects. The author of "The Pleasures of Memory," upon the authority of Prevost, adopts the notion of bees being near-sighted: "Hark! the bee winds her small but mellow horn, Who guides the patient pilgrim to her cell? Of varied scents that charm'd her as she flew ? Hail! Memory, hail! thy universal reign Guards the least link of being's glorious chain." But unfortunately for this poetical fancy, it does not accord with the facts; for independently of *The Honey-Bee, p. 311. The Bees, a Poem. Bevan on the Honey-Bee, p. 314. the practice of bees flying, as Huber has stated, straight to and from the hive, we have in numerous instances seen a bee search the same blossom two or three times in the course of a few minutes, in utter forgetfulness of having already plundered it of its honey *. If Réaumur, however, be correct in his opinion, as we are inclined to think he is, these apparent discrepancies may be easily reconciled; for he attempts to show, that bees and most other insects are endowed with two sorts of eyes, one for distant, and another for near vision; instead of having the power as we have of adapting the eye to various distances, the nature of which adaptation is not well understood t. In order to understand this more precisely, it will be necessary to enter into a few details as to the number and structure of the eyes of insects. It may at first appear not a little puzzling to con. ceive how a spider with eight eyes, a centipede with twenty, and a butterfly with thirty-five thousand facets in its two eyes, can perceive only one object; yet the difficulty is not of a very different kind from that of our own two eyes representing only a single object and not two,-a subject which has exercised the ingenuity of many a philosopher. Vandermonde ‡, for example, supposed that children at first see double, and correct the error by experience; an opinion adopted by Blumenbach: Dr. Reid referred it to an original and inexplicable law of human nature §, confessing thereby his inability to explain it ; and some of the old philosophers satisfied themselves that it was because the nerve from each eye meets * J. R. + Des Cartes, Mariotte, Jurine, Dr. T. Young, Mr. C. Bell, Mr. Travers, &c. have given various opinions on this subject. Apud Haller, Physiol. Inquiry into the Human Mind. before reaching the brain. The latter would have perhaps been satisfactory, had it not been refuted by the simple experiment of pushing one of the eyes a little aside, when objects will be seen double, though this cannot alter the meeting of the nerves. Dr. Wells explains it by the coincidence of what he calls the visible direction *. Whatever opinion be adopted, it is evident that most creatures can see an object by using one eye only, sometimes better than when both are employed. The celebrated painter, Leonardo da Vinci, upon this principle recommended his pupils always to look at distant objects with one eye only †, and we have frequently observed in birds, particularly those which feed on insects (Sylviada, Merulidæ, &c.), that on looking out for prey, they most commonly turn their head on one side, so as to bring only one eye to bear on the object. A thrush always does so when he examines a snail-shell that he means to attack, and a red-breast before he pounces upon a worm. It is no doubt for this very reason that the wryneck (Yunx torquilla) is enabled to move its head in the manner from which it derives its popular name; and many insects, such as the dragon-flies (Libellulina), can turn their heads nearly round about; though, from the great volume of their eyes, this might almost be considered superfluous. Most spiders have eight, though some only six eyes, and these are so variously arranged, that their positions have been employed by systematic writers for distinguishing the genera and species; and as it may not only be useful for this purpose, but illustrative of the subject immediately before us, we shall here give figures of the position of the eyes of a number of spiders. Phil. Trans. for 1792 and 1811. † Mem. d'Acad., Berlin, 1768, p. 80. 0 a, Eyes of Mygale avicularia. Ο 00 b, Eyes of Mygale cœmentaria-and c, Lycosa vorax. م d, Eyes of Dolomedes marginatus—and e, Ctenus dubius. h f, Eyes of Sphasus indianus-and g, Attus parus. 9 h, Eyes of Eresus cinnaberinus—and i, Thomisus citreus. k, Eyes of Clubiona accentuata-and 1, Dysdera erythrina. |