MAMMALIA. 397 
Jn others, again, they assume diverse degrees of development, more or less 
elongated, as, for instance, in those which are used for clasping or seizing. 
They are longer and thinner when destined only to walk or to dig. In 
some mammals, the thumb is opposed to the other fingers or toes, so that it 
works with the latter as a pincer. Jn this case, the feet are called hands. 
The use of the thumb is sometimes also very much reduced. 
Generally, the extremities of the toes terminate by horny bodies, which 
are called hoofs, when they surround all the toes at once; nails, when they 
present themselves as mere plates on the upper surface and extremity of the 
toes ; and finally claws, when they are compressed, pointed, curved, seldom 
straight, and inserted above at the extremity of the toes. When the claws 
approach nearer to the nature of the hoof, they are then called hoof-nails. 
Sloths and ant-eaters, when at rest, can bend backwards their long claws 
under the sole of the foot, whilst most of the cats and carnivora retract 
them into a fold of the skin. The two- -hoofed mammals, and the hogs and 
the allied genera, besides the developed toes which are surrounded by the 
hoof, have usually two small rudimentary ones, provided with hoofs, which 
are called posterior hoofs, placed above and posterior to the true hoofs. 
The males of Ornithorhynchus and of Echidna possess, on the heels of the 
hind feet, a horny spur. The horny envelope sometimes is wanting to 
many toes, and this is especially the case for the thumb of a few genera. 
Sometimes, also, the toes are partly or entirely soldered together, or they 
are united into a membrane fitted for swimming. This membrane some- 
times extends beyond the tips of the toes, and sometimes reaches only half 
their length (semi-palmated feet). The fore feet of Cetacea are in a very 
rudimentary state, and the hind feet are completely wanting. 
For their protection and their defence, the mammals are provided with 
teeth, claws, or hoofs, and with antlers or horns. The elephant defends 
itself not only by means of the tusks, but also with its proboscis ; the skunk 
discharges at its enemy a fetid fluid, secreted by special anal glands: 
others attempt to escape by flight, or by feigned death; still others have 
spines, scales, or bony cuirasses, as means of defence. The quadrumana, 
or monkeys, make use of surrounding objects, as stones and sticks, to keep 
off their enemies. 
The male lives either with one female alone or with several. The female 
brings forth young either once only or several times a year; and in the 
colder regions, this takes place during the warmest season. The female of 
most genera prepares for its young a don bed; those only whose young can 
see a walk, or swim, immediately after birth, as is the case with the hoofed 
mammals, the seals and cetacea, &c., do not provide such a litter, nor do 
those which carry about their young. The young of other mammals are 
very weak when just born, and are often unable to see before nine or four- 
teen days. ‘he number of young at a birth varies; usually less as the 
animal is greater. The hog, however, constitutes an exception. Dogs, 
foxes, and cats bring forth three to six at a birth. The young are first 
suckled by the mother, and as long as she feeds them she displays towards 
them the warmest affection, exposing herself to every danger in protecting 
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