as the moles and bats, have the molars terminated by several

sharp, conical points, (Fig. 74,) so arranged that the eleva tions of one tooth fit exactly into the depressions of the tooth opposite to it. In the true Carnivora, (Fig. 75,) on the contrary, the molars are compressed laterally, so as to have sharp, cutting edges, as in the bats; and they shut by the side of each other, like the blades of scissors, thereby dividing the food with great facility.

220. The same adaptation is observed in the teeth of herbivorous animals. Those which chew the cud, (ruminants,) many of the thick-skinned animals, (pachydermata,) like the elephant, and some of the gnawers, (rodentia,) like the hare, (Fig. 76,) have the summits of the molars flat, like mill-stones, with more or less prominent ridges, for grinding the grass and leaves on which they subsist. Finally, the omnivora, those which feed on both flesh and fruit, like man and the

monkeys, have the molars terminating in several rounded tubercles, being thus adapted to the mixed nature of their food.

221. Again, the mode in which the molars are combined with the canines and incisors furnishes excellent means of characterizing families and genera. Even the internal structure of the teeth is so peculiar in each group of animals, and yet subject to such invariable rules, that it is possible to determine with precision the general structure of an animal,

merely by investigating the fragment of a tooth under a mi

croscope.

222. Ar ther process, subsidiary to digestion, is called insalivation. Animals which masticate their food have glands, in the neighborhood of the mouth, which secrete a fluid called saliva. This fluid mingles with the food as it is chewed, and prepares it also to be more readily swallowed. The salivary glands are generally wanting, or rudimentary, or otherwise modified, in animals which swallow their food without mastication. After it has been masticated and mingled with saliva, it is moved backwards by the tongue, and passes down through the œsophagus, into the stomach. This act is called deglutition or swallowing.

223. The wisdom and skill of the Creator is strikingly illustrated in the means he has afforded to every creature for securing the means for subsistence. Some animals have no ability to move from place to place, but are fixed to the soil; as the oyster, the polyp, &c. These are dependent for subsistence upon such food as may stray or float near, and they have the means of securing it when it comes within their reach. The oyster closes its shell, and thus entraps its prey; the polyp has flexible arms, (Fig. 77,) capable of

P

m

great extension, which it throws instantly around any minute animal that comes in contact with it. The cuttle-fish, also, has elongated arms about the mouth, furnished with ranges of suckers, by which it secures its prey, (Fig. 47.)

224. Some are provided with instruments Fig. 77 for extracting food from places which would be otherwise inaccessible. Some of the mollusks, with their rasp-like tongue, (Fig. 58,) perforate the shells of other animals, and thus reach and extract the inhabitant. Insects have various piercers, suckers, or a protractile tongue for the

same purpose, (Figs. 61-64.) Many Annelides, the leeches for example, have a sucker, which enables them to produce a vacuum, and thereby draw out blood from the perforations they make in other animals. Many microscopic animals are provided with hairs or cilia around the mouth, (Fig. 65,) which by their incessant motion produce currents that bring within reach the still more minute creatures or particles on which they feed.

225. Among the Vertebrata, the herbivora generally employ their lips or their tongue, or both together, for seizing the grass or leaves they feed upon. The carnivora use their jaws, teeth, and especially their claws, which are long, sharp even movable, and admirably adapted for the purpose. The woodpeckers have long, bony tongues, barbed at the tip, with which they draw out insects from deep holes and crevices in the bark of trees. Some reptiles also use their tongue to take their prey. Thus, the chameleon obtains flies at a distance of three or four inches, by darting out his tongue, the enlarged end of which is covered with a glutinous substance to which they adhere. The elephant, whose tusks and short neck prevent him from bringing his mouth to the ground, has the nose prolonged into a trunk, which he uses with great dexterity for bringing food and drink to his mouth. Doubtless the mastodon, once so abundant in this country, was furnished with a similar organ. Man and the monkeys employ the hand exclusively, for prehension.

226. Some animals drink by suction, like the ox, others by lapping, like the dog. Birds simply fil. the beak with water, then, raising the head, allow it to run down into the crop. It is difficult to say how far aquatic animals require water with their food; it seems, however, impossible that they should swallow their prey without introducing at the same time some water into their stomach. Of many among the lowest animals, such as the Polyps it is well

known that they frequently fill the whole cavity of their body with water, through the mouth, the tentacles, and pores upon the sides, and empty it at intervals through the same openings. And thus the aquatic mollusks introduce water into special cavities of the body, or between their tissues, through various openings, while others pump it into their blood vessels, through pores at the surface of their body. This is the case with most fishes.

226 a. Besides the more conspicuous organs above described, there are among the lower animals various microscopic apparatus for securing their prey. The lassos of polypi have been already mentioned incidentally, (223.) They are minute cells, each containing a thin thread coiled up in its cavity, which may be thrown out by inversion, and extend to a considerable length beyond the sac to which it is at tached. Such lassos are grouped in clusters upon the tenacles, or scattered upon the sides of the Actinia and of most polypi. They occur also in similar clusters upon the tentacles and the disk of jelly-fishes. The nettling sensation produced by the contact of many of these animals is undoubtedly owing to the lasso cells. Upon most of the smaller animals, they act as a sudden, deadly poison. In Echinoderms, such as star-fishes, and sea-urchins, we find other microscopic organs in the form of clasps, placed upor. a movable stalk. The clasps, which may open and shut alternately, are composed of serrated or hooked branches, generally three in number, closing concentrically upon each other. With these weapons, star-fishes not more than two inches in diameter may seize and retain shrimps of half that length, notwithstanding their efforts to disentangle themselves.

CHAPTER SEVENTH.

CF THE BLOOD AND CIRCULATION.

227. THE nutritive portions of the food are poured into the general mass of fluid which pervades every part of the body, out of which every tissue is originally constructed, and from time to time renewed. This fluid, in the general acceptation of the term, is called blood; but it differs greatly in its essential constitution in the different groups of the Animal Kingdom. In polypi and medusæ, it is merely chyme, (208;) in most mollusks and articulates it is chyle, (209) but in vertebrates it is more highly organized, and constitutes what is properly called BLOOD.

228. The BLOOD, when examined by the microscope, is found to consist of a transparent fluid, the serum, consisting chiefly of albumen, fibrin, and water, in which float many rounded, somewhat compressed bodies, called blood disks.

These vary in number with the natural heat of the animal from which the blood is taken. Thus, they are more nu