*Aberrant. Forms or groups of animals or plants which deviate in important characters from their nearest allies, so as not to be easily included in the same group with them, are said to be aberrant.

*Abnormal. Contrary to the general rule.

*Aborted. An organ is said to be aborted when its development has been arrested at a very early stage.

AËrate (ZoÖl.). To subject to the influence of the air by the natural organs of respiration; to arterialize; especially used of animals not having lungs.

Agnostic (a.). Professing ignorance; involving no dogmatic assertion; leaving a question or problem still in doubt; pertaining to or involving agnosticism.

Agnostic (n.). One who professes ignorance, or refrains from dogmatic assertion; one who supports agnosticism, neither affirming nor denying the existence of a personal Deity.

Agnosticism. That doctrine which, professing ignorance, neither asserts nor denies; specifically, in theology, the doctrine that the existence of a personal Deity can be neither asserted nor denied, neither proved nor disproved, because of the necessary limits of the human mind (as sometimes charged upon Hamilton and Mansel), or because of the insufficiency of the evidence furnished by psychical and physical data, to warrant a positive conclusion (as taught by the school of Herbert Spencer); opposed alike to dogmatic skepticism and to dogmatic theism.

Allantois, Allantoid. A thin membrane, situated between the chorion and amnion, and forming one of the membranes which invest the foetus.

*Analogy. That resemblance of structures which depends upon similarity of function, as in the wings of insects and birds. Such structures are said to be analogous, and to be analogues of each other.

Anthropomorphism. The representation of the Deity under a human form, or with human attributes.

*Articulata. A great division of the animal kingdom, characterized generally by having the surface of the body divided into rings, called segments, a greater or less number of which are furnished with jointed legs (such as insects, crustaceans, and centipeds).

Articulation (Anat.). The joining or juncture of the bones of a skeleton.

Ascidians. A class of acephalous mollusks, having often a leathery exterior.

Biology. The science of life; that part of physiology which treats of life in general, or of the different forces of life.

Brain. The upper part of the head. 1. (Anat.) The whitish, soft mass which constitutes the anterior or cephalic extremity of the nervous system in man and other vertebrates, occupying the upper cavity of the skull; and (b) the anterior or cephalic ganglion in insects and other invertebrates.

2. The organ or seat of intellect; hence, the understanding.

3. The affections; fancy; imagination.

*BranchiÆ. Gills, or organs for respiration in water.

*Branchial. Pertaining to gills or branchiÆ.

*CanidÆ. The dog family, including the dog, wolf, fox, jackal, etc.

Cell. A minute, inclosed space or sac, filled with fluid, making up the cellular tissue of plants, and of many parts of animals, and originating the parts by their growth and reproduction; the constituent element of all plants and animals (though not universal for all parts of such structure), much as a crystalline molecule is the element of a crystal. In the simplest plants and animals (as the infusoria), one single cell constitutes the complete individual, such species being called unicellular plants or animals.

Cephalopod (Fr. cÉphalopode, from Gr., head and foot). (ZoÖl.) An animal of the sub-kingdom Mollusca, characterized by a distinct head, surrounded by a circle of long arms or tentacles, which they use for crawling and for seizing objects. See Mollusk.

*Cetacea. An order of Mammalia, including the whales, dolphins, etc., having the form of the body fish-like, the skin naked, and only the fore-limbs developed.

Chaos. 1. An empty, infinite space; a yawning chasm.

2. The rude, confused state, or unorganized condition, of matter before the creation of the universe.

Consciousness. 1. The knowledge of sensations and mental operations, or of what passes in one's own mind; the act of the mind which makes known an internal object.

2. Immediate knowledge of any object whatever.

*Crustaceans. A class of articulated animals having the skin of the body generally more or less hardened by the deposition of calcareous matter, breathing by means of gills. (Examples, crab, lobster, shrimp, etc.)

Dynamically. In accordance with the principles of dynamics or moving forces.

*Embryo. The young animal undergoing development within the egg or womb.

*Embryology. The study of the development of the embryo.

Ethics. The science of human duty; the body of rules of duty drawn from this science; a particular system of principles and rules concerning duty, whether true or false; rules of practice in respect to a single class of human actions; as political or social ethics.

*Fauna. The totality of the animals naturally inhabiting a certain country or region, or which have lived during a given geological period.

Fetichism, Feticism. One of the lowest and grossest forms of superstition, consisting in the worship of some material object, as a stone, a tree, or an animal, often casually selected; practiced among tribes of lowest mental endowment, as certain races of negroes.

*Flora. The totality of the plants growing naturally in a country or during a given geological period.

*Foetal. Of or belonging to the foetus, or embryo in course of development.

Foetus, same as Fetus. The young of viviparous animals in the womb, and of oviparous animals in the egg, after it is perfectly formed, before which time it is called embryo.

*Ganoid Fishes. Fishes covered with peculiar enameled bony scales. Most of them are extinct.

Genus (Science). An assemblage of species possessing certain characters in common, by which they are distinguished from all others. It is subordinate to tribe and sub-tribe; hence, a single species having distinctive characters that seem of more than specific value may constitute a genus.

*Germinal Vesicle. A minute vesicle in the eggs of animals, from which the development of the embryo proceeds.

Gravitation (Physics). That species of attraction or force by which all bodies or particles of matter in the universe tend toward each other; called also attraction of gravitation, universal gravitation, and universal gravity.

Gravity (Physics). The tendency of a mass of matter toward a center of attraction; especially the tendency of a body toward the center of the earth, terrestrial gravitation.

Gyrus, pl. Gyri (Anat.). A convolution of the brain.

*Habitat. The locality in which a plant or animal naturally lives.

Heredity. The transmission of the physical and psychical qualities of parents to their offspring; the biological law by which living beings tend to repeat themselves in their descendants.

Homologous. Having the same relative proportion, position, value, or structure; especially—(a) (Geom.) Corresponding in relative position and proportion. (b) (Alg.) Having the same relative proportion or value, as the two antecedents or the two consequents of a proportion. (c) (Chem.) Being of the same chemical type or series; differing by a multiple or arithmetical ratio in certain constituents, while the physical qualities are wholly analogous, with small relative differences, as if corresponding to a series of parallels; as, the species in the group of alcohols are said to be homologous. (d) (ZoÖl.) Being of the same typical structure; having like relations to a fundamental type of structure; as, those bones in the hand of man and the fore-foot of a horse are homologous that correspond in their structural relations—that is, in their relations to the type-structure of the fore-limb in vertebrates.

Homology. That relation between parts which results from their development from corresponding embryonic parts, either in different animals, as in the case of the arm of a man, the fore-leg of a quadruped, and the wing of a bird; or in the same individual, as in the case of the fore and hind legs in quadrupeds, and the segments or rings and their appendages of which the body of a worm, a centiped, etc., is composed. The latter is called serial homology. The parts which stand in such a relation to each other are said to be homologous, and one such part or organ is called the homologue of the other. In different plants the parts of the flower are homologous, and in general these parts are regarded as homologous with leaves.

Hypothesis. 1. A supposition; a proposition or principle which is supposed or taken for granted, in order to draw a conclusion or inference for proof of the point in question; something not proved, but assumed for the purpose of argument.

2. A system or theory imagined or assumed to account for known facts or phenomena.

Imago. The perfect (generally winged) reproductive state of an insect.

Implacenta (n.). A mammal having no placenta. (a.) Without a placenta, as certain marsupial animals.

Insectivorous. Feeding on insects.

Instinct (n.). Inward impulse; unconscious, involuntary, or unreasoning prompting to action; a disposition to any mode of action, whether bodily or spiritual, without a distinct apprehension of the end or object which Nature has designed should be accomplished thereby; specifically, the natural, unreasoning impulse in an animal, by which it is guided to the performance of any action, without thought of improvement in the method.

Invertebrata, or Invertebrate Animals. Those animals which do not possess a backbone or spinal column.

Isomeric (from Gr., equal and part). (Chem.) Having the quality of isomerism; as isomeric compounds.

Isomerism (Chem.). An identity of elements and of atomic proportions with a difference in the amount combined in the compound molecule, and of its essential qualities; as in the case of the physically unlike compounds of carbon and hydrogen, consisting one of one part of each, another of two parts of each, and a third of four of each.

Kangaroo. A ruminating marsupial animal of the genus Macropus, found in Australia and the neighboring islands.

Larva (plural LarvÆ). The first condition of an insect at its issuing from the egg, when it is usually in the form of a grub, caterpillar, or maggot.

LemuridÆ. A group of four-handed animals, distinct from the monkeys, and approaching the insectivorous quadrupeds in some of their characters and habits. Its members have the nostrils curved or twisted, and a claw instead of a nail upon the first finger of the hind hands.

Lepidosiren. An eel-shaped animal covered with rounded scales, having four rod-like members, and breathing water like a fish. It is found in ponds and rivers of intertropical Africa and South America. By some it is regarded as a fish, and by others as a batrachian.

Mammal. Belonging to the breast; from mamma, the breast or pap. An animal of the highest class of vertebrates, characterized by the female suckling its young.

Mammalia. The highest class of animals, including the ordinary hairy quadrupeds, the whales, and man, and characterized by the production of living young, which are nourished after birth by milk from the teats (mammÆ, mammary glands) of the mother. A striking difference in embryonic development has led to the division of this class into two great groups: in one of these, when the embryo has attained a certain stage, a vascular connection, called the placenta, is formed between the embryo and the mother; in the other this is wanting, and the young are produced in a very incomplete state. The former, including the greater part of the class, are called placental mammals; the latter, or aplacental mammals, include the marsupials and monotremes (ornithorhynchus).

Marsupials. An order of Mammalia in which the young are born in a very incomplete state of development, and carried by the mother, while sucking, in a ventral pouch (marsupium), such as the kangaroos, opossums, etc. (see Mammalia).

Molecule. A mass; one of the invisible particles supposed to constitute matter of any kind.

Mollusk. An invertebrate animal, having a soft, fleshy body (whence the name), which is inarticulate, and not radiate internally.

Monkey. See Simia.

Monogamy. A marriage to one wife only, or the state of such as are restricted to a single wife, or may not marry again after the death of a first wife.

Monotheism. The doctrine or belief that there is but one God.

Morphology. The law of form or structure independent of function.

Nascent. Commencing development.

Nexus. Connection; tie.

Nictitating Membrane. A semi-transparent membrane, which can be drawn across the eye in birds and reptiles, either to moderate the effects of a strong light or to sweep particles of dust, etc., from the surface of the eye.

Noumenon (Metaph.). The of itself unknown and unknowable rational object, or thing in itself, which is distinguished from the phenomenon in which it occurs to apprehension, and by which it is interpreted and understood; so used in the philosophy of Kant and his followers.

Opossum. An animal of several species of marsupial quadrupeds of the genus Didelphys. The common species of the United States is the D. Virginiana. Another species, common in Texas and California, is D. Californica, and other species are found in South America.

Organism. An organized being, whether plant or animal.

Ovule. An egg. (Bot.) The rudimentary state of a seed. It consists essentially of a nucleus developed directly from the placenta.

Parasite. An animal or plant living upon or in, and at the expense of, another organism.

Pelvis. The bony arch to which the hind-limbs of vertebrate animals are articulated.

Placentalia, Placentata, or Placental Mammals. See Mammalia.

Protozoa. The lowest great division of the Animal Kingdom. These animals are composed of a gelatinous material, and show scarcely any trace of distinct organs. The infusoria, foraminifera, and sponges, with some other forms, belong to this division.

Phenomenon. 1. An appearance; anything visible; whatever is presented to the eye; whatever, in matter or spirit, is apparent to, or is apprehended by, observation, as distinguished from its ground, substance, or unknown constitution; as phenomena of heat or electricity; phenomena of imagination or memory.

2. Sometimes a remarkable or unusual appearance whose cause is not immediately obvious.

Plexus. Any net-work of vessels, nerves, or fibers.

Polygamy. A plurality of wives or husbands at the same time, or the having of such plurality; usually the condition of a man having more than one wife.

Polytheism. The doctrine of a plurality of gods or invisible beings superior to man, and having an agency in the government of the world.

Proteine (n. Lat., proteinum, from Gr., first—to be the first—the first place, chief rank, because it occupies the first place in relation to the albuminous principles). (Chem.) A substance claimed by Mulder to be obtained as a distinct substance from albumen, fibrine, or caseine, and considered by him to be the basis of animal tissue and of some substances of vegetable origin.

The theory of proteine can not be maintained.—Gregory.

The theory of Mulder is doubted and denied by many chemists, and also the existence of proteine as a distinct substance.

Psychology. A discourse or treatise on the human soul; the science of the human soul; specifically, the systematic or scientific knowledge of the powers and functions of the human soul, so far as they are known by consciousness.

Quadrumane. An animal having four feet that correspond to the hands of a man, as a monkey.

Race. 1. The descendants of a common ancestor; a family, tribe, people, or nation, believed or presumed to belong to the same stock; a lineage; a breed.

2. A root.

Retina. The delicate inner coat of the eye, formed by nervous filaments spreading from the optic nerve, and serving for the perception of the impressions produced by light.

Rotifer (n. Lat. rotifer, from Lat. rota, a wheel, and ferro, to bear. Fr. rotifÈre). (ZoÖl.) One of a group of microscopic crustaceans, having no limbs, and moving by means of rows of cilia about the head or the anterior extremity.

Rudiment (Nat. Hist.). An imperfect organ, or one which is never fully formed.

Sacral. Belonging to the sacrum, or the bone composed usually of two or more united vertebrÆ to which the sides of the pelvis in vertebrate animals are attached.

Sacrum. The bone which forms the posterior part of the pelvis. It is triangular in form.

Secularize. To convert from spiritual to secular or common use; as to secularize a church, or church property.

Segments. The transverse rings of which the body of an articulate animal or annelid is composed.

Simia (plural SimiadÆ) (Lat., an ape, from simus, flat-nosed, snub-nosed). (ZoÖl.) A LinnÆan genus of animals, including the ape, monkey, and the like; a general name of the various tribes of monkeys.

Species (Nat. Hist.). A permanent class of existing things or beings, associated according to attributes or properties which are determined by scientific observation.

Spinal Cord. The central portion of the nervous system in the vertebrata, which descends from the brain through the arches of the vertebrÆ, and gives off nearly all the nerves to the various organs of the body.

Statical. To stand. 1. Pertaining to bodies at rest, or in equilibrium.

2. Resting; acting by mere weight without motion; as statical pressure.

Sulcus. A fissure of the brain, separating two convolutions, or gyri.

Teleology (Fr., tÉlÉologie, from Gr., the end or issue, and discourse). The science or doctrine of the final causes of things; the philosophical consideration of final causes in general.

Variety (Nat. Hist., Bot., and ZoÖl.). Any form or condition of structure under a species which differs in its characteristics from those typical to the species, as in color, shape, size, and the like, and which is capable either of perpetuating itself for a period, or of being perpetuated by artificial means; also, any of the various forms under a species meeting the conditions mentioned. A form characterized by an abnormity of structure, or any difference from the type that is not capable of being perpetuated through two or more generations, is not called a variety.

Vascular. Containing blood-vessels.

Vertebrata; or Vertebrate Animals. The highest division of the animal kingdom, so called from the presence in most cases of a back-bone composed of numerous joints or vertebrÆ, which constitutes the center of the skeleton, and at the same time supports and protects the central parts of the nervous system.

Vesicle. A bladder-like vessel; a membranous cavity; a cyst; a cell; especially (a) (Bot.) a small bladder-like body in the substance of a vegetable, or upon the surface of a leaf.—Gray. (b) (Med.) A small orbicular elevation of the cuticle containing lymph, and succeeded by a scurf or laminated scab; also, any small cavity or sac in the human body; as the umbilical vesicle.

Vortices (verto, to turn). 1. A whirling or circular motion of any fluid, usually of water, forming a kind of cavity in the center of the circle, and in some instances drawing in water or absorbing other things; a whirlpool.

2. A whirling of the air; a whirlwind.

3. (Cartesian system.) A supposed collection of particles of very subtile matter, endowed with a rapid rotary motion around an axis. By means of these vortices Descartes attempted to account for the formation of the universe.