Animal
2 of the 7 encyclopedias on this shelf carry an entry for Animal. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
ordinarily an organism that grows, lives, and feels. It is difficult to give a definition that will separate all animals from all plants. It is easy to point out the difference between the higher animals and higher plants. The horse and the cow, for instance, are different from the elm and the rose; but it is difficult to distinguish between the lower animals and the lower plants. Scientists have long been in doubt whether to call bacteria plants or animals. It is only of late that the decision has been given that they are plants. Both animals and plants grow, so growth does not help us out. It will hardly do to say that an animal feels and that a plant does not, for certain plants seem to be as sensitive as some animals. The sundew and other insect-catching plants are extremely sensitive. Most animals move about, yet a sponge remains fixed. Some large aquatic plants float about without sending their roots into the soil. Many microscopic plants seem to have power of moving toward food. At their beginning, then, the animal and vegetable kingdoms seem quite on a level, and are almost indistinguishable; but the animal kingdom, with man at its head, far out-tops the vegetable kingdom. By scientists animals are distinguished from plants principally by the difference in the nature of the food of each. Animals can live on substances not differing much, if at all, from the substances composing their own bodies. They can also use solid food. Plants take their food in the form of gases or fluids only. A certain number of low forms seem to combine the characters of animals and plants, and the classification of these forms can be determined only after a special study of each case. However much animals may differ among themselves, they are all alike in certain fundamental respects. All animals are composed of a complex living proteid substance, called protoplasm. This living substance may occur naked, or surrounded by a thin membrane; but it is always accompanied by a substance called nuclein, which is found in the nucleus. A bit of protoplasm with a nucleus is called a cell. Neither protoplasm nor nucleus can exist if separated, but each soon dies. Some animals consist of only one cell, while others are built up of a countless number of cells. Not only are all animals alike in that they are composed of protoplasm, but all animals take food which they digest and assimilate. All animals are able to throw off waste matter. All animals grow and reproduce. But the differences between animals are perhaps more striking than the similarities; and were observed much earlier. Thus it has long been known that birds differ from fishes and that both differ from frogs and reptiles. It is very easy to see that horses differ from cows, and both from sheep. Since there are millions of differing animals known, they have been separated into types, or classes, for the sake of convenience. All the animals in each type resemble each other in some important respects, and differ from the animals in other types in these respects. Authorities differ in regard to the number of types which exist, but agree in placing the number between nine and twelve. Animals which are made up of only one cell are called Protozoa, and constitute Type I. Plant-like, fixed animals, made up of many cells, in the form of a modified vase or cylinder with perforated sides, constitute Type II, and are called Porifera. Other types of many-celled animals are the Coelenterata, the Vermes, the Molluscoidea, the Echinodermata, the Annulata, the Arthropoda, the Mollusca, and the Chordata. But animals resembling each other sufficiently to be classified together under one type may differ from each other in certain less important respects. Therefore it has been found necessary to divide each type into classes, each class into orders, each order into families, each family into genera, each genus into species. Thus, if the full classification of the domestic cat were to be given, he would be placed under the type Chordata, because he agrees with fishes, frogs, reptiles, birds, and mammals in having a notochord in his early developmental stages. He would furthermore be included in the class Mam-malia, because, like all mammals, the cat possesses mammary or milk glands. He would be placed in the order Carnivora, because he is a flesheater; in the family Felidae, because he possesses retractile claws, has a short face, and teeth differing from other members of the Carnivora. The cat is placed in the genus Felis, because he differs in size and color from other Felidae, like lions, tigers, and panthers. And lastly, he is placed in a different species from the wild cat, because he has changed in habit, size, and color as a result of domestication. In a tabulated form the classification of the domestic cat would appear as follows: Kingdom Animalia Type Chordata Class Mammalia Order Carnivora Family Felidae Genus Felis Species Felis domestica Every animal is classified according to some such scheme as this. Animals inhabit the land, the water, or the air. The science which treats of them is called zoology.--ELLEN TORELLE. See Amoeba ; Sponge ; Earthworm ; Clam ; Lamprey ; Fish ; Birds; Frog ; Reptile; Mammals ; Insects ; Mollusks ; and numerous articles on the different animals. On the intellectual side, alas, the more we come to know of the minds of animals, the more monumental appears the ignorance and stupidity of the best of them. Speaking roughly, the relation of animal ability to human ability is this: If we start with the average successful business or professional man, and from this level drop down through a certain interval of natural capacity, we reach the grade of the ordinary day-laborer. Another drop, equal in amount, brings us to the lowest savages. One more of the same sort, and we reach the level of children of four, of weak-minded men and idiots, of dogs and cats and monkeys and elephants. Still lower comes the general ruck of animals. It is a hard saying. But what does any actual animal ever do that is beyond the mental power of a human idiot?--E. T. Brewster in McClure's Magazine. Lynx. Carnivorous animals Spotted hyena. Carnivorous animals 2026 Editor's Note: The blurry line this entry frets over was redrawn entirely: biologists now sort life into several kingdoms and three great domains , and DNA — not appearance — decides kinship. The bacteria it can't classify turned out to belong to branches of life all their own, as different from animals and plants as those are from each other. (Ed: BR 2026-07-14)
Collier's New Encyclopedia (1921)
an organized and sentient living being. Life in the earlier periods of natural history was attributed almost exclusively to animals. With the progress of science, however, it was extended to plants. In the case of the higher animals and plants there is no difficulty in assigning the individual to one of the two great kingdoms of organic nature, but in their lowest manifestations, the vegetable and animal kingdoms are brought into such immediate contact that it becomes almost impossible to assign them precise limits, and to say with certainty where the one begins and the other ends. With regard to internal structure no line of demarkation can be laid down, all plants and animals being, in this respect, fundamentally similar; that is, alike composed of molecular, cellular, and fibrous tissues. Neither are the chemical characters of animal and vegetable substances more distinct. Animals contain in their tissue and fluids a larger proportion of nit nitrogen than plants, while plants are richer in carbonaceous compounds than the former. Power of motion, again, though broadly distinctive of animals, cannot be said to be absolutely characteristic of them. Thus many animals, as oysters, sponges, corals, etc., in their mature condition are rooted or fixed, while the embryos of many plants, together with numerous fully developed forms, are endowed with locomotive power by means of vibratile, hair-like processes called cilia. The distinctive points between animals and plants which are most to be relied on are those derived from the nature and mode of assimilation of the food. Plants feed on inorganic matters, consisting of water, ammonia, carbonic acid, and mineral matters. They can only take in food which is presented to them in a liquid or gaseous state. The exceptions to these rules are found chiefly in the case of plants which live parasitically on other plants or on animals, in which cases the plant may be said to feed on organic matters, represented by juices of their hosts. Animals, on the contrary, require organized matters for food. They feed either upon plants or upon other animals. Animals require a due supply of oxygen gas for their sustenance, this gas being used in respiration. Plants, on the contrary, require carbonic acid. The animal exhales or gives out carbonic acid as the part result of its tissue waste, while the plant taking in this gas is enabled to decompose it into its constituent carbon and oxygen. The plant retains the former for the uses of its economy, and liberates the oxygen, which is thus restored to the atmosphere for the use of the animal. Animals receive their food into the interior of their bodies, and assimilation takes place in their internal surfaces. Plants, on the other hand, receive their food into their external surfaces, and assimilation is effected in the external parts, as are exemplified in the leaf surfaces under the influence of sunlight. All animals possess a certain amount of heat or temperature which is necessary for the performance of vital action. The only classes of animals in which a constantly elevated temperature is kept up are birds and mammals.