As to the second sub-order, it contains some very curious forms. The typical lemurs (which inhabit Madagascar) have long fox-like snouts and long tails. Certain African forms (the genus _Galago_) are very active in their movements, and great leapers. A tailless group (the slender loris) is interesting, as presenting a diminutive quasi-human form, reflected, as it were, through a Lemurine prism, just as the rat-mole shows us a mole-form reflected through a rodent prism. A little animal, the Tarsier, which is found on the islands of Celebes and Borneo, is very exceptional in its structure. Still more so is the aye-aye (_Cheiromys_). This very remarkable species was discovered by Sonnerat in Madagascar in 1770, and was never again seen till 1844, when a specimen was forwarded to Paris. It has now, however, become well known. Inhabiting the sea are many beasts, which are, by mistake, popularly spoken of as "fishes." Such are the whales and the porpoises--animals which, in spite of their form and habit, suckle their young, and have hot blood, as all other mammals have. These creatures form an order by themselves, called _Cetacea_. Another order of aquatic beasts is termed _Sirenia_, and the animals which compose it were long confounded with the _Cetacea_, from which, however, they are widely divergent in structure, in spite of the general similarity which exists between them in external appearance. The order _Sirenia_ contains but two existing genera. One of these is the now well-known manatee (_Manatus_), the other is the dugong (_Halicore_)--an animal very similar to the manatee, and found in the rivers of regions about the Indian Ocean. A third form, the _Rhytina_, existed in the Aleutian Isles till recent times, but was extirpated almost as soon as discovered, from its incapacity for flight or defence, and from its flesh affording a welcome change of diet to hungry sailors. The _Cetacea_ and _Sirenia_ are examples of creatures organized for a completely aquatic life--for never coming to land. The forest-regions of South America offer to animal life so enormous a mass of foliage that it may not unjustly be termed a sea of verdure, and creatures there exist which are specially organized for a completely arboreal life--for never coming to the ground. Such creatures are the sloths, which pass their lives hanging back-downwards, suspended to the branches by their huge claws. Thus, they sleep without effort (from the peculiar mechanism of their limbs), and they move slowly from tree to tree, having no need to hurry after food, since they live suspended in the midst of a perennial banquet.