rat-mole (Spalax). The jerboa has very long hind legs, and a habit of jumping, so that it resembles superficially (but not really) a small kangaroo. The Spalax is quite blind, and has the burrowing habit, and somewhat the shape of the common mole. Some rodents are fitted to flit through the air in long jumps, by means of the wide extensibility of the skin of their flanks, which, when stretched out, acts as a parachute. Such forms are the flying squirrels, and a curious rodent called Anomalurus, from the exceptional clothing of the base of its tail, which is furnished with large scales at its under part.

Another order of beasts may here be referred to, because it affords interesting examples of the co-existence of external resemblance without any real affinity. This order includes the insect-eating beasts, or Insectivora, and comprises the moles, hedgehogs, shrew-mice (which are not really "mice" at all), and their allies. The Insectivora and Rodentia present us with a singular parallelism in the respective modifications of structure, which are found in these two very distinct orders. But the insectivorous forms (as might perhaps be expected from their less abundant food) are always smaller in size than are the parallel vegetable-eating groups of rodents. Indeed, one insectivore of the genus Sorex (the shrew-mouse genus) is the absolutely smallest mammal which is known to exist.

As examples of the parallelism referred to may be mentioned the moles (which resemble the rat-moles), the shrew-mice (which resemble true mice), the hedgehogs, and the less known spiny tanrec of Madagascar (which resemble porcupines in their clothing); certain graceful and active tree-frequenting insectivores of the Indian Archipelago, Tupaia (which resemble squirrels); an aquatic African form, Potomogale (which resembles the musk-rat); certain elephant shrews—long-legged, jumping, African insectivores (which resemble the jerboa amongst rodents); and, lastly, the so-called flying lemur of the Philippine Islands, or Galeopithecus, which resembles the flying squirrel, and the curious rodent Anomalurus before referred to.

The only beasts, however, which truly fly are the bats, which form an order by themselves, well-named, from the structure of their wings, Cheiroptera. The bats which fly about in the twilight in this country, or sometimes in the afternoon of a warm day in winter, are all insect-eating forms. But in the warm regions of the Old World, and of Australia, there are large fruit-eating kinds, called "flying foxes;" while in South America there are blood-sucking bats, or vampires, some of which, as we shall hereafter see, present the most curious and interesting modifications of structure in harmony with their peculiar habits.

The creatures which are in some respects the most interesting to us, because they are the most like ourselves in form, are the apes. Moreover, not only are they so like us in form, but they are so widely marked-off from all other creatures except ourselves, that it seems impossible they can have any real affinity to one more than to another group of mammals below man. Apes and man then together form one order, which as ranking first was named by Linnæus, Primates. With the apes are commonly associated certain animals called Lemurs, which inhabit the vicinity of the Indian Ocean, especially Madagascar. They have not, however, any real affinity to apes; and if they are to be placed in the same order at all, they must be well distinguished from its other members. It has therefore been proposed[12] to divide the order Primates into two sub-orders (as the hoofed order is divided into the "odd-toed" and "even-toed" sub-orders), one of these to include man and apes, and to be called, from the resemblance to the human form pervading it, "Anthropoidea;" the other sub-order to be termed "Lemuroidea."

The first "sub-order" is divisible into three "families." One of these (Hominidæ) contains man (forming the genus Homo), the second (Simiadæ) contains all the apes of the Old World only, while a third (Cebidæ) contains all those of America.

Amongst the Simiadæ are the orang, the chimpanzee, the gorilla, and the long-armed apes (or Gibbons), which are the most man-like of all the apes; and there can be no question but that there is very much less difference in structure between these four kinds of apes and man, than there is between them and the lowest of the apes—i.e., the marmosets.

Concerning this resemblance, Buffon has observed, when speaking of the ape, the most man-like (and so man-like) as to brain:[13] "Il ne pense pas: y a-t-il une preuve plus évidente que la matière seule, quoique parfaitement organisée, ne peut produire ni la pensée, ni la parole qui en est le signe, à moins qu'elle ne soit animée par un principe supérieur?"

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