sorts of chickens and doves which are to be seen in zoological gardens, or in the court-yards of poultry fanciers, did not exist 100 years ago-this variety owes its existence to human industry. In the same way the forms of plants and animals have been modified by natural conditions, by the differences in the soil, the food, and the climate, etc. The Bible says nothing about the extent of the variation of plants and animals; how many of the different kinds now enumerated in the handbooks of botany and zoology have been formed in the course of ages, and how many kinds God originally created, are purely questions for natural science.

The general opinion of scientific men hitherto has been that there exists a certain number of groups of organic beings, although it cannot be accurately determined how many, which are separate from and independent of one another and which have always possessed certain characteristic and distinguishing signs. These groups must therefore have originated singly and separate from one another; according to the Biblical teaching, their ancestors were created by God. These groups are called species, and Linnæus sums up the ordinary view in the sentence: "Species tot sunt diversæ, quot diversas formas ab initio creavit infinitum ens.' "There are as many different species as there were different forms created in the beginning by the Infinite Being." Linnæus even thought, as I have mentioned before, that each species had been created in the shape of one pair, and that all individuals of one species had, like men, the same ancestors. I have already shown that the Bible does not say this; on the contrary, it is just

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as little in accordance with the Biblical account as it is scientifically conceivable. Neither does the Bible or history tell us, nor can it be discovered with certainty by scientific inquiry, how many species were originally created, and therefore how many species there are. But though it should appear that one group which constitutes one species in the Linnæan system should be divided into two or more species, or that several species of the Linnæan system must be considered as forming one species, yet Linnæus' main idea would not be affected.

Linnæus combined the species which are most nearly connected together into larger groups which he called genera, and since then it has become customary to connect the names of the genus and species together in the systematic enumerations of plants and animals. The domestic cat, e.g., is Felis domestica, the wild cat, Felis catus, the tiger, Felis tigris, the lion, Felis leo, the panther, Felis pardus, the jaguar, Felis onca. These six beasts of prey are therefore species of one and the same genus, Felis. In botany in the same way seven kinds of pines are called species of the one genus, Pinus; the pine, Pinus abies, the fir, Pinus picea, the larch, pinus larix, etc. Linnæus includes the genera which are most like each other into the so-called order, Ordines; the orders which most resemble each other in classes. This division has been much modified by later writers, but we need say no more about it here, we are only concerned with the kinds or species.

Now men of science are at variance as to the meaning and the extent of the word "species." In

dividuals which spring from the same parents undoubtedly belong to the same species; but of course the genealogy of individuals can only be proved to a very small extent and in exceptional cases. Cuvier gives us the following definition, "All the individual animals and plants which can be proved to descend from one another, or from common parents, or which resemble the latter as much as the latter resemble each other, belong to the same species." The last part of this definition is unsatisfactory, because no criterion of likeness is adduced. Later writers, therefore, have given other definitions, and have especially laid stress on the fact that any qualities belonging to a species which are found in all the individuals of a group, and which are permanent and lasting, that is, which do not alter through all the generations of the animals and plants in question, must be held to be characteristic distinguishing marks of that species. Virchow says: "Species is the name generally given by scientific men to those living beings which reproduce themselves from generation to generation with similar qualities, with a certain sameness of internal constitution and of outward appearance, and in which, therefore, certain qualities and signs are hereditarily transmitted."1

1 Die Lehre Darwins, Deutsche Jahrbücher, vi. 431. "In this question of species it does not signify whether the divergences are great or small, or whether they consist in so called essential or unessential details. From a practical point of view the decisive question is, whether differences of any kind are and remain lasting. If it is proved that these differences appear in the course of development, that is, where new individuals branch off, and that they remain and do not merge again, they must be considered as characteristic, and the individuals possessing them belong to a group of forms, they are one and the same kind, they constitute a genealogical unit. Individuals and groups in which the resemblance of the separate members is great enough to

Of course, besides the resemblances which characterize all the individuals of a species, we find individual differences. If one egg never completely resembles another, still less are two horses, two dogs, etc., exactly alike. There is conformity in the essential qualities which remain the same through all generations, and there is difference in the unessential qualities.

Those groups of individuals of the same species which resemble one another as to such unessential qualities, and which yet differ from the great mass of individuals, are called varieties; and if the peculiarities of these varieties become hereditary, there arise what are called races. Poodles, greyhounds, bull-dogs, terriers, etc., are, for instance, different races of the species dog; the dog, the wolf, the fox, etc., are different species of the genus Canis; Canis domesticus, Canis lupus, Canis vulpus. "The race," says Virchow, "forms a separate series within the species, which, however far we may go back, branches off once from the common root, and does not again amalgamate with it," but remains true to its own peculiarities; "the varieties, on the other hand, represent branches from the stem, which often repeat themselves, which occur as it were under the warrant our assuming that blood relationship exists between them, can only be considered as belonging provisionally to one species. . . . It is evident that the larger number of the groups of individuals which are called species in books, can only be looked upon as such provisionally. The distinctive criterion of the species is blood relationship; individuals which can be proved to be related by blood form a species. Therefore those individuals who are not genetically connected, cannot be specifically connected. According to this, the essence of species is blood relationship, and those groups of forms which are related by blood, and can always be distinguished from other forms by characteristic signs, but which are not transition forms, constitute a species. These, therefore, show us the extent of a species." Herm. Hoffmann, Untersuchungen, etc. p. 21.

eyes of the observer, and sometimes produce progeny with the qualities of the original ancestry;"1 as, for instance, we find that flowers which regularly produce white blossoms sometimes produce red; while from the seeds of the latter, after a few generations, white flowers will again spring. The varieties and races have therefore formed themselves in the course of time; the species, on the other hand, have existed from the beginning.

It is also a characteristic of species, that where an intermixture of animals of different species takes place the progeny does not remain fertile. For instance, horses and donkeys, which form different species of the same genus, can together bring forth mules, but these are sterile; and even where hybrids of different species are fertile, the power of reproduction dies out in the second or third generation, while the fertility of couples taken from different races of the same species undergoes no diminution. De Quatrefages says: "Crossbreeding shows us plainly the fundamental difference between the species and the race in animals and plants. The intercrossing of species, 'hybridation,' that is, the bringing forth of hybrids, occurs very seldom in nature. If it occurs by the interposition of man, the progeny is in most cases barren. If fertility lasts through some generations, it almost always diminishes considerably. On the other hand, the intercrossing of races," which de Quatrefages calls metissage in contradistinction to hybridation, "occurs often in nature, and is always just as productive as the intercrossing of individuals of the same race,—very often the fertility is markedly 1 Op. cit. p. 341.