SPECIES, a group of individuals which agree in exhibiting certain distinctive hereditary characters of sufficient importance to render a particular name convenient. When we famil iarly talk of the different °kinds° of plants and animals, we indicate in a rough way the biological ideal of species; and the recognition of raven, jackdaw and rook, as different kinds of crow, corresponds with the scientific distinc tion of these as four different species of the genus Corms. (See GENUS). In many a case, however, where the distinctive hereditary char acters are less conspicuous, the ordinary ob server may see only one grind° where the trained naturalist detects many °speries.• Moreover, where a naturalist unfamiliar with the details of a particular class of animals might discern only half a dozen distinct species, the specialist might distinguish a score. In fact, the conception of species is entirely rela tive to convenience; where the "lumpers think a score of special groups with special names quite sufficient, the °splitters° may think it necessary to distinguish a hundred. Except in cases where the limitations of group from group are very clear, as in the case of the four °kinds° of crow above mentioned, it requires a period of criticism before a satisfactory com promise between the °lumpers° and the °split ters° can be arrived at. And the reason for this is simply that in many cases one species is linked to another by intermediate varieties, and, it may be, also by hybrids.
Collections of definitions of °species° have often been made; and the curious will find a score in Quatrefages' posthumous work, 'Dar win et ses precurseurs Francais.' Thus, Lin
flans wrote: "Species tot numeramus quot diverse forme in principio sunt create.° Buf fon defined species as "a constant succession of individuals similar to, and capable of reproduc ing each other." De Candolle said that a species was "an assemblage of all those individuals which resemble each other more than they do others, and which are able to reproduce their like, in such a manner that they may be sup posed by analogy to have descended from a single being or a single pair.° Quatrefages' idea of species is summed up in his statement that it is "an assemblage of individuals more or less resembling one another, which are de scended, or may be regarded as being descended, from a single pair by an uninterrupted succes sion of families.° Muller says species is a "living form, represented by individual beings, which reappears in the product of generation with certain invariable characters, and is con stantly reproduced by the generative act of similar individuals.° These illustrations may suffice to impress the fact that the invariable nature of species had become firmly fixed on the minds of the older naturalists in former years.
A species, it may safely be concluded, repre sents no immutable, fixed or unvarying group, but a very variable one, differing widely in the extent of its variation in different cases. A species is a relative and subjective conception ; the reality is in the component individuals. See