“The Owls,” said Uncle Thomas, on their next meeting, “are perhaps one of the most interesting families of Birds of Prey. They are, with one or two exceptions, night birds; that is, they seek their prey during the night, or in the dim twilight when scarcely any other animal can see.” “But how, then, can they perceive their prey?” asked Jane. “By a peculiar formation,” said Uncle Thomas, “the eye of the Owl has been fitted for use just when from the habits of the bird it is most wanted. The pupil of its eye, which, when there is little light, expands to a great extent, and enables it to see distinctly the smallest objects, is of such extreme sensibility that if light is admitted it contracts, and prevents the bird from seeing at all. You will understand this better if you examine carefully the eye of a Cat, which to a certain extent has the same property as that of the Owl. When it is subjected to a moderate light, you will perceive that the pupil is of a certain size, but if a much stronger light is admitted it contracts till you scarcely perceive it, and in this state it is nearly as useless as if it was covered by the eyelid.” “But Cats can see to hunt in the sunshine,” said Mary; “I saw Puss watching some birds in the garden to-day.” “Though I used the Cat’s eye as an illustration,” said Uncle Thomas, “I did not mean you to understand that those of the Owl and it are exactly the same. From possessing less sensibility, perhaps, that of the Cat can be used in broad day-light, when the Owl is nearly blind. Accordingly, when one happens to be dislodged by any accident during sunshine, it is immediately attacked with impunity by whole flocks of small birds, who never cease their persecutions till it again finds refuge in some dark and snug retreat. “Besides this singular power of vision, which it has in common with all animals which seek their prey in the twilight,” continued Uncle Thomas, “the Owl has other peculiarities in its structure, which are in a great measure confined to itself. Its skull is larger in proportion to the size of the bird than that of most other animals, and the bone is thin and fine, so that no space is lost, nor is it troubled with more weight than is absolutely necessary. A considerable part of the interior of the skull is occupied by two large cavities, in which the nerve by which the impression of sound is conveyed to the brain is expanded to an unusual size, and thus the sense of hearing is much more acute than in most other animals.” “What can it want with this?” asked Harry. “At night, when every thing is so still there can be no difficulty in hearing, I should think.”