MAMMALIA 79 the elephant, the goat, and the horse ; 4 in the cow, the stag, and the lion ; 8 in the cat ; 10 in the hog, rabbit, and rat ; and 12 or 14 in the agouti. The position also varies; in monkeys and bats they are on the chest, in most carnivora on the chest and abdomen, and in the ruminants far back between the pos- terior limbs ; in marsupials they are concealed within the abdominal pouch. Some mammals are born with the eyes open, and are at once able to run in search of food ; many, however, are born with the eyes closed and in a very weak condition ; and a few, as the marsupials, leave the uterus in such an imperfect state that they would perish did not the parent place them in her pouch, where they complete their development, each suspended to a teat. In the monotremata (ornithorhynchus, &c.), which seem to form the connecting link between the mammals and birds, in addition to the horny bill, cloaca, and bird-like ovaries, there are the form, external covering, skeleton, and milk- secreting glands of the mammals. As to phys- ical distribution, some mammals dwell entirely in the sea, as the cetaceans and most seals ; some of the latter and the sirenoid pachyderms (manatee, &c.), live chiefly in fresh water ; others, beavers, muskrats, the ornithorhyn- chus, &c., frequent rivers and lakes ; but most live upon the land, some on mountains like the chamois and ibex, some on plains like the antelopes and bison, some on trees like the apes, squirrels, and sloths ; others sail or fly in the air like the flying lemur and the bats, and others live under ground like the moles. For these different methods of progression and habits of life, the limbs are variously adapted by modifications of the same few osseous ele- ments, and the study of fossil mammals de- velops the same order in past geological ages. The study of the geographical distribution of mammals shows that the number of genera and species increases from the poles to the equator, with the exception of the whales and seals, which are most numerous in the polar regions ; within the northern arctic circle there are spe- cies common to both hemispheres, as the arc- tic fox, white bear, reindeer, and ermine ; in temperate North America the species are dif- ferent from those of the eastern hemisphere, and in South America even the genera from those of the old world, as those including the peccary, llama, armadillo, ant-eater, sloth, cavy, agouti, vampire bat, marmoset, the howling and prehensile-tailed monkeys ; the raccoon and muskrat are exclusively American; the hog, horse, camel, rhinoceros, elephant, lion, tiger, lemurs, and anthropoid apes belong now to the eastern world ; the giraffe, hippopotamus, chimpanzee, and most of the antelopes, are African ; all the marsupials (except the Ameri- can opossums) and the monotremata are Aus- tralian, while the stags, squirrels, cats, bears, dogs, and bats are absent from this region. The marsupials, though forming scarcely one fifteenth of the land mammals in the world, 527 VOL. xi. 6 constitute three fourths of the mammalian fauna of Australia ; exclusive of cetaceans and seals, the rodents form one third of the entire number of species of the world, the bats and carnivora one third, the remaining third being chiefly the monkeys, ruminants, marsupials, and insectivora, according to Van der Hoeven ; in Europe, wanting marsupials and monkeys, the rodents are one third, bats one sixth, and insectivora about one thirteenth; in North America the species of rodents form perhaps half the entire number of land mammals ; the large pachyderms, edentates, and the apes be- long to the warm regions, most of the latter being African ; the insectivora are almost pe- culiar to the northern hemisphere, and the le- murs are most common in the southern. Ex- cepting the whales and bats, mammals do not migrate, but spend the summer and winter in the same locality ; the whales pass the summer in the polar regions, and come southward in winter into the lower Atlantic. The phenom- ena of hibernation or winter-sleep in mammals have been described under the former title. MAMMALOGY includes the classification of mam- malia. The mammalia were first separated from other four-footed animals by Aristotle, who called them zootoca or viviparous animals ; he divided them into three sections according to their locomotive organs : 1, dipoda, or bipeds; 2, tetrapoda, or quadrupeds ; 3, apoda, impeds or whales. The quadrupeds, including all but man and the cetaceans, he subdivided into two great groups according to the modifications of the organs of touch, in the first of which the ends of the digits are left free for the sense of feeling, the nail being on the upper surface only, and in the second the feet ending in hoofs, corresponding respectively to the un- guiculata and ungulata of Ray. The unguicu- lates he divided by the teeth into three fami- lies : 1, those with cutting incisors and tritu- rating or flattened molars, like the apes (pithe- coida) and the bats (dermaptera) ; 2, those with canine or carnivorous teeth, carcharo- donta or gampsonucha ; 3, those correspond- ing to the rodents, with the negative character of the absence of canine teeth. The ungulate or hoofed quadrupeds he divided, according to the organs of motion, into : 1, polysckida or multungulates, like the elephant ; 2, dischidcs or bisulcates, including the ruminants (mery- cizonta) and the hogs ; and 3, aschidce, or so- lidungulates, like the horse. The apodal quad- rupeds included the cetaceans or cetoda. It thus appears that Aristotle clearly perceived the principles upon which mammals are classi- fied by the best modern naturalists. This ar- rangement was not improved upon until John Ray published his Synopsis in 1693 in London, and his improvements relate to the four-foot- ed mammals. In his ungulate quadrupeds he places the solipedous (as the horse), the bisul- cate ruminants (like the ox and stag) or non- ruminants (as the hog), and the quadrisulcate (rhinoceros and hippopotamus) ; in the un-
