EYE IN VERTEBRATES. Passing now to the con sideration of the vertebrate eye, we find that the structure is in all eases essentially similar to that of the human eye, though many cases of degenerate eyes are known. associated with some peculiarities of habit, as, in the hagfish, with a parasitic mode of life: or. as in the cave salaman ders and fishes, with living in the dark. (See CAPE ANIMALS.) In fishes the eyes have little power of movement, the cornea is very flat, and the lens is globular; the eyes are thus accom modated. when at rest, for seeing near objects. The sclerotic is frequently calcified or ossified, and there is no eiliary muscle. In amphibians the eyes are somewhat simpler than in fishes, but the eiliary muscle is present as in all higher vertebrates. In both fishes and amphibians we find examples of angular pupils. In reptiles the eye shows slight advance in structure, in respect to some special peculiarities; thus. in lizards there is a ring of bony sclerotic plates and a curious structure, the 'pecten' (also present in snakes, crocodilians. and especially in birds), the
function of which is in dispute, some saying, it is concerned solely with the nutrition of the eye, others that it aids in accommodation. In birds the eyeball is not nearly spherical (as in other vertebrates), but is elongated so that it is m nob deeper than high. This is most marked in owls. In mammals the sclerotic is entirely librous, the external surface of the lens is less convex than the internal, and there is 110 pecten. The pupil may be round, transversely oval, or have the form of a vertical slit. In aquatic mammals the cornea is flattened as in fishes.
Boni OGRAPII Y. 'Lang, Text-Book of ('ompara tive Anatomy (New York, 1896) ; Wiedersheim, Comparative Anatomy of Vertebrates (Now York, 1886) ; Carriere, Die Sehoryane der Thiere (Mun ich and Leipzig, 1885).