We are, then, in default of a physiological experimentation analogous to what the monogenists require, in attempting to prove that the crossing of two species of animals is or is not eugenesic, reduced to the impressions, or rather appreciation of observers. Most of these appreciations can only be approximatives wanting a fixed basis. It is absolutely unknown what is the relative proportion of mulattoes of the first degree who intermarry between themselves, and such who intermix with other mestizos, or with individuals of a pure race; nor can we know what, in a given population, should be the normal proportion of these mulattos if they were perfectly prolific _between themselves_. It then becomes very difficult to say whether the number of mulattoes issued in a direct line from mestizos of the first degree is equal to the normal proportion, or inferior to it; so that, if they are but little inferior to their parents in regard to fecundity, the fact might pass unobserved. The relative sterility of these breeds would only become evident when it approaches absolute sterility. Between this degree of prolifickness and perfect fecundity there are many intermediate degrees, difficult to recognise, and still more difficult to prove. The first French observer who has denied the prolifickness of mulattoes is M. Jacquinot, author of the zoological part of the _Voyage to the South Pole and Oceania_. We shall reproduce here some passages from that work. After having spoken of the cross-breeds of animals, M. Jacquinot continues in the following terms:[26] “It is the same in the human genus. There the species are very approximating, and, according to the principles just laid down, ‘that the more species are approximating the greater the chance of fecundity,’ the mestizos issuing from the intermixture enjoy a certain degree of prolifickness which, however, as in animals, is not absolute. Like the latter, they return to the mother’s species in allying themselves with them; and, independently of their relative fecundity, new individuals are constantly produced by the union of the parent races. “On observing in our colonies that a population of mulattos is constantly produced and renewed, their fecundity was not doubted; yet it is very limited. On the one hand the mulattos disappear every moment in one or the other of the parent races, and if their unions were constantly between themselves, they would not be long before becoming extinct.... “In a colony, that is to say in an island, or a part of a continent of limited extent peopled by Negroes and white men for some centuries, the greater part of the population should be composed of mulattoes....