Species
in biology, a somewhat amother countries. group of organisms, resembling each other, and capable of reproducing similar organisms, animal or vegetable, as the case may be. A species is defined by Haeckel as "the sum of all cycles of reproduction which, under similar conditions of existence, exhibit similar forms." Linnæus held that all species were the B SPECIFIC GRAVITY Buffon and direct descendants from and had the characters of primevally created forms, and in this he was followed by those who a strictly literal sense. accepted the first chapter of Genesis in ity of reproduction. But besides varieon one side, held the distinguishing marks animals and plants, dimorphism, and in ity of reproduction. But besides varieties and races in various species of and the value attached to external reothers trimorphism, exists, so that close and the value attached to external reent observers. At a later date was added semblances varies in the case of different observers. At a later date was added the physiological definition that all the individuals of every species were capable of producing fertile offspring by intercrossing, whereas sexual intercourse between different species produced only sterile offspring or was actually infertile; and, though subject to exceptions, this definition is generally true. The descent of any given series of individuals from a single pair, or from pairs exactly similar to each other, is in no case capable of proof. says: "I look at the term species as one arbitrarily given for the sake of conresembling each other, and that it does says: "I look at the term species as one venience to a set of individuals closely not essentially differ from the term varesembling each other, and that it does riety, which is given to less distinct and IAN THEORY). That book popularized the idea of the mutability of species, the be Natural Selection, though he afterbe Natural Selection, though he afterward modified his views to some extent as to its importance. A later theory of the origin of species is that of Physiological Selection, propounded by W. G. Romanes, F. R. S., who holds that many species have arisen on account of variations in the reproductive system, infertility with parent variations in the reproductive system, leading to some infe forms-mutual sterility being thus regarded as one of the conditions, and not as one of the consequences of specific differentiation.
In logic, a predicable that expresses the whole essence of its subject in so far as any common term can express it. The names species and genus are merely relative, and the same common term may in one case be the species which is other case the individual of which a species is predicated. Thus the individual, George, belongs to the logical species man, while man is an individual of the logical species animal.
SPECIFIC GRAVITY. See GRAVITY, SPECIFIC.
Cyc-VoL IX SPECK VON STERNBURG