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.