ORGANS of Menem.
Tun organs of motion differ considerably in the va rious classes of animals. In many they are as distinct as in man, and much more powerful in proportion ; while in others, though the phenomena of motion are very apparent, the organs by which it is produced, can not be with certainty ascertained.
The general differences of the bony system which constitute the distinguishing marks between the verte bral and invertebral animals need not be here repeated. The composition and structure of the bony system are extremely various. In the MAMM ALIA, the texture of the bones is seldom so fine and delicate as in man, though it is for the most part proportionally stronger. In some species, the fibres are much more loose, and the cellular texture more distinct than in man. This is particularly the case with the CETACEA. The bones of BIRDS have much larger cavities than those of all other animals ; but these cavities are filled with air instead of marrow. The hones of REPTILES and FISHES have a very homogeneous appearance ; the gelatinous and earthy parts being uniformly mixed. The bones of fishes have a large proportion of gelatinous matter, and in some tribes they are wholly cartilaginous. The horns of some animals, as the various species of deer, very nearly resemble the bones of the rest of the body, but those of other animals ; as the cow, the sheep, Sec. have a superabundance of gelatinous and albuminous matter, and are formed of plates lying over each other, not being of a reticulated structure as in the former. The shel ly covering of the turtle tribe nearly resembles these latter horns. The shells of the testacea have a great proportion of earthy matter, but this is chiefly carbonate of lime, while the earthy part of the bones of vertebral animals is cciefly phosphate of lime.
Many of the ZOOPHYTES are attached to a stem that is composed partly of animal matter, but chiefly of a concrete earthy substance, resembling the matter of the testaceous shells. This is the case with all those marine productions called corallines, 7nadrepores, pores, Sec.
In the muscular system there is a striking difference with respect to the colour of the fibres. In all the AlAmmALIA, in CETACEA, and in BIRDS, the muscular fibres are red, while in all the other classes they are white. The muscles of the MA MM A L IA differ but little from those of man, except in being proportionally stronger in beasts of prey, and others that are accustom ed to great exertions. In birds that fly, the muscles attached to the wings are most remarkable for their size and strength. The fleshy part of the muscles of BIRDS is said to lose its irritability sooner than in those of other animals, and the tendons are more disposed to become bony. In REPTILES, the muscles are fewer in number than in other vertebral animals ; but some of them are of prodigious strength. In SERPENTS, on the other hand, they are proportionally more numerous, but more thin and uniform. In most FISHES the muscles are dis posed in layers, producing those flakes which we ob serve in the flesh of these animals when cooked. They are very numerous and large, of a uniform texture, and in general destitute of tendinous fibres. In the CRUS TA c EA, the muscles are seldom very numerous, but those which move the large claws in the crabs and lob sters, are particularly strong and fleshy. INSECTS have generally a great number of muscular fibres, but these are not collected into fleshy bundles, as in other animals. The lary of insects are endowed with a much greater number of muscles than even serpents; some minute naturalists having counted in one larva above 4000; and these in several individuals appear to be possessed of immense strength.
Most of the MOLLUSC A have numerous and very strong muscles. In those which crawl or swim, there is a very compact tissue of fleshy fibres, below the skin, which adapts them to these motions. In the testacea there are particular muscles for fastening the animals to their shelly covering ; and in some of the naked acephala, there is a peculiar fleshy body surrounding the animal, called its cloak.