kinds, depends also upon peculiar structures. The ankle-bones are very long in these, so long, indeed, as to make the foot resemble that of a Frog when jumping more than that of any other animal. The long ankle-bone acts as part of a lever, and enables the muscles of the back of the leg to act on the foot so as to project the creature high in the air, or for many feet from one bough to another, or along the ground. There is nothing like this in the Monkeys. Now, the woolly fur of the Lemuroids, and their cylindrical woolly tails, at first sight appear to be encumbrances to an active animal which lives in the tropics, but they are all extremely chilly creatures, and love heat; moreover, it is possible that severe falls may be rendered less injurious by the deadening influence of a soft fur. The tail is a wonderful apparatus in some kinds, and barely exists in others, being, however, never prehensile even when longest and strongest. Probably it is used as a kind of adjuster of movements in rapid exercise, and certainly it is a great comfort to many, for several kinds like to curl it over their backs, or round their necks, like a sable boa, whilst they are asleep, or basking in the sun. In one kind it is supplied with a marvellous set of tendons, and, indeed, to such an extent of complexity, that it would appear that Nature had lavished mechanical appliances to every joint without any very definite use. It is remarkable that in those Lemuroida which have no tail, or barely a trace, there is a curious arrangement of the blood-vessels. The limbs in these kinds are not supplied with main arteries, and veins with long branches, but the blood-vessels form a closely-packed set of tubes of very small size. This network, in the language of science, is called a _rete mirabile_, “a wonderful network,” for such it is. Curiously enough this arrangement of the blood-vessels is found in some totally different animals, whose movements are very slow and cautious, such as the Sloths, for instance. Equally slow are the movements of some of the kinds of Lemuroida which possess this interesting structure. It has been suggested that this novel division and subdivision of the blood-vessels tends to produce slowness of movement, and it may be said in a general way that the active Lemuroida and active animals of other orders do not have a _rete mirabile_. [Illustration: HEAD OF INDRIS (PROPITHECUS) VERRAUXII, TO SHOW LEMUROID NOSTRILS. (_After Grandidier._)]