The complete retractility of the claws is a very distinctive feature of the true Cats. It is brought about in this way: the terminal joint of the toe, which is clad with the claw, folds back into a sheath by the outer side of or above the middle phalanx. It is held in this position by a strong ligament. The flexor muscles straighten the phalanx which bears the claw, so that the natural position for the animal is to be in a state of retracted claws, which of course preserves them from friction; when wanted for aggressive purposes, they are pulled into sight by the action of the muscles already mentioned. [Illustration] FIG. 194.--The phalanges of the middle digit of the manus of the Lion (_Felis leo_). x 1/2. _a_, The central portion forming the internal support to the horny claw; _b_, the bony lamina reflected around the base of the claw; _ph_^1, proximal phalanx; _ph_^2, middle phalanx; _ph_^3, ungual phalanx. (From Flower's _Osteology_.) Much has been written as to the shape of the pupil of the Cat's eye. Some careful observations upon the matter have been {392} made by Dr. Lindsay Johnson,[269] who found that out of 180 Domestic Cats 111 had round pupils, and that in 19 the shape was a pointed oval, intermediate conditions being offered by the rest. These 180 comprised males and females of many varieties. When the pupil of the Cat's eye contracts, it forms a vertical slit with two pin holes, one at each end, through which alone light appears to enter. In the Genet and the Civet the contraction of the pupil is as in the Cat. In the Lion, Tiger--in fact apparently in all the large Cats--the pupil retains its circular shape even when contraction is fully effected. Dr. Johnson has, furthermore,[270] made some interesting experiments upon the Seal's eye--a creature which has, of course, to exert its powers of vision in two media, and from one to the other. This is effected by dilatation of the pupil when in the water, and its contraction to a vertical slit with parallel margins and rounded ends when in the air, the contraction being to some extent at least under the influence of the animal's will.