And yet

mongrels produced every day under our eyes. the material conditions of fertility are identically the same with races as with species, and our botanical gardens, which group numbers of species side by side, facilitate crossing still

more.

rare.

Among wild animals living in liberty hybrids are still more It is unknown, for example, among mammalia, according to Isidore Geoffroy, whose experience has here a double value. The order of birds alone presents some facts of this kind, nearly all of which are in the order of Gallinæ. According to Valenciennes, they are unknown among fishes. In domestication and captivity spontaneous crossing between different species is a little less rare.

The intelligent intervention of man has multiplied unions of this kind in a remarkable manner, especially among plants, but without being able to extend their limits. Linnæus thought crossing was possible between species of different families. But in 1761 Koebreuter showed that he was mistaken. From these investigations, which were carried on for twenty-seven years, and from those of M. Naudin, his worthy rival, it appears that artificial crossing between species of different families never succeeds, and very rarely between species of different genera; that it is always very difficult, and demands the most minute precautions to insure success; that it often fails between species of the same genus closely allied in appearance, and finally, that there are whole families among which hybrids are impossible. Amongst the latter figures the family of the cucurbitaceæ, so thoroughly studied by M. Naudin, where the most perfect mongrels were produced spontaneously. We could not imagine, evidently, a more complete contrast.

This contrast is carried into the minutest details. For example, any flower which has in the least possible degree undergone the action of pollen of its own species becomes absolutely insensible to the action of pollen of a different species. How different to the equality of action displayed by the several pollens of most distant races I

All experimenters agree further in declaring that even in the unions between species which have been most successful, the fertility is constantly diminished, and often in immense proportions. The head of the Papaver somnifera generally contains 2000 seeds or more. In a hybrid of this species Gærtner only found six which had been matured; all the rest were more or less abortive. Here again, what a contrast between the crossing productive of such fertility in M. De Ginestous' English pigs.

Hybridism in animals presents exactly the same phenomena as in plants. Man has been able, by diverting and deceiving animal instincts, to multiply crosses between species. But he has not been able to extend the very narrow limits at which these phenomena cease. Not one fertile union has taken place between different families; they are very rare between genera, and even between species they are far from numerous, a fact the more remarkable as animal hybridation is an ancient institution. The mule was known to the Hebrews before the time of David, and to the Greeks in the age of Homer. Titires and musmons, products of crossings between the he-goat and the sheep and the ram with the she-goat, received their distinctive names from the Romans.

The uncertainty of the result is another point of resemblance between animal and vegetable hybrids. The same experiments executed with the same care and by equally clever experimenters have sometimes succeeded and sometimes failed without any apparent cause. Buffon and Daubenson often tried to reproduce titires and musmons. They succeeded twice, while Isidore Geoffroy has invariably failed. The formation of crosses between the hare and the rabbit, which has frequently been attempted in various parts of the globe, appears only to have been successful four or five times at the most. The pretended cross between the camel and the dromedary, admitted by Buffon and quoted by Nott, is certainly a fable, after the details which M. De Khanikoff kindly gave me, and which I have published elsewhere. We may, therefore, draw this conclusion from known facts, that

there are only two species of mammals, the ass and the horse, the crossing of which is almost universally and invariably fertile.

Finally, crossing between species, or hybridation, is extremely exceptional among plants and animals when left to themselves; man can only produce them with great difficulty in the two kingdoms, and then only between a very limited number of species; when he has succeeded, the fertility is almost constantly diminished, and often to a very considerable extent.

CHAPTER VIII

CROSSING BETWEEN VEGETABLE AND ANIMAL RACES AND SPECIES; MONGRELS AND HYBRIDS; REALITY OF SPECIES.

I. FROM the very first, in the union of two individuals belonging to different stocks, the race and the species display very distinct and characteristic phenomena. We shall now see this opposition as strongly marked in the product of these unions in mongrels and hybrids.

Several questions are raised by the mixed nature of these beings. I shall confine myself to those which refer to filiation, and which have therefore a special interest for us. They may be stated generally as follows:-are mongrel races, that is, those derived from two distinct races, and hybrid races, that is those which are derived from the crossing of two species, formed naturally, or can they be obtained artificially? In other words, do mongrels and hybrids retain, during an indefinite number of generations, the faculty of reproducing and transmitting to their descendants the mixed character they inherited from the first parents which effected the cross?

II. In regard to mongrels there is not a shadow of doubt. Facts which frequently occur, often without our intervention, and sometimes in spite of our precautions, prove again and again that the mongrels of the first generation are as fertile as the parents, and transmit equal fertility to their offspring. Our gardeners and breeders always take advantage of this property of mongrels in order to vary, modify or ameliorate from their point of view the plants and animals in which they are interested; the careful experiments of Buffon, of Geoffroy St. Hilaire, father and son, and

the testimony of Darwin, on this point very significant, prove beyond a doubt that unions between different races remain fertile, whatever morphological differences there may be between them. I shall confine myself to quoting one example from Darwin. The niata will unite indifferently in both senses with the ordinary ox, and the offspring is fertile.

If several races of a single species are in habitual contact and left to themselves, they will intermix in every degree. This results in bastard offspring, devoid of definite characters, but which, when methodically studied, would lead through insensible shades to the different primitive types. In this manner our street dogs and cats have come into existence, which remain perfectly fertile in spite of innumerable crossings of every kind.

With human intervention it is possible, when care is taken, to regulate the crossing between two races, and to obtain a mongrel race. After a few oscillations between the paternal and maternal types it becomes consolidated and settled. But whatever constancy it may have acquired as a whole, it almost always happens that some individuals reproduce, to a varying extent, the characters of one of the types originally crossed.

This phenomenon is designated by the name of Atavism. It sometimes occurs in the midst of a race considered to be perfectly pure, and is the result of a single crossing several generations back. Darwin quotes the case of a breeder, who having crossed his fowls with the Malay race, wished afterwards to free them from the strange blood. After spending forty years in the attempt, he is still unsuccessful, the Malay blood always reappearing in some of his fowls.

In animals as in plants, universal, free and indefinite fertility, whether between themselves or between all the races of the same species, is one of the characters of mongrels. Atavism attests the physiological bond which unites all mongrels.