Between the higher apes, or between any of the apes and any known antecedent and different animal, no naturalist has discovered the intermediate link or links. Darwin supposes that there was some one extremely ancient progenitor from which proceeded the two main divisions of the _Simiadæ_--namely, the Catarrhine and Platyrhine monkeys, with their sub-groups. This extremely ancient progenitor is nothing but a scientific hypothesis; or, to use a legal phrase, it had nothing but a constructive existence. It is necessary to believe in the principle of evolution, in order to work out the hypothesis of this creature from which the two great stems of the _Simiadæ_ are supposed to have proceeded. Here, then, we have the case of a pedigree or succession of animal races, the _propositum_ of which has no known existence. Next we have two known divisions of the _Simiadæ_, or monkeys; but, between them and their imaginary common progenitor, we have no known intermediate animals constituting the gradations of structure from the progenitor to the descendants. The whole chain has to be made out by tracing resemblances among the animals of a certain class that are known, then applying these resemblances to the supposed divergencies from the structure of a supposed progenitor, and then drawing the conclusion that there was such a progenitor. It may be submitted to the common sense of mankind, whether this is a state of facts which will warrant scientists or philosophers in using toward those who do not accept their theory quite so much of the _de haut en bas_ style of remark as we find in the writings of Mr. Spencer.[77] If the researches of geologists had ever discovered any remains of an animal that would fulfill the requirements, and thus stand as the progenitor of the _Simiadæ_. By the case would correspond to that of a known individual from whom we undertake to trace the descent of another individual through many intermediates; and in such a case strong family resemblances of various kinds might possibly afford some aid in making out the pedigree as a reliable conclusion. But there is no means of connecting the Old World and the New World apes with any but an unknown and imaginary, progenitor. Darwin himself frankly tells us that "the early progenitor of the whole Simian stock, including man," is an undiscovered animal, which may not have been identical with, or may not even have closely resembled, any existing ape or monkey.[78]