The question here is, not whether descent of organisms from organisms, with modifications upon modifications, is a supposable theory, but whether it is so satisfactorily shown that it can be said to exclude the hypothesis of a special creation of each organism. There may be parts of structure in one animal which seem to have no functional use, although we should be cautious in making the assumption that they are of no use because we have not yet discovered that use. But let it be assumed that these apparently useless parts in one animal correspond to parts which in another animal are functionally useful. If there was established for these two separately created animals a like system of procreation and gestation, that system, affected at the same time by a law of growth imposed by the special type of the species, might in one species lead to the presence of parts of which we can not recognize the use, and might in other species lead to the presence of parts of which we can see the use. It does not help to a better explanation to say that there has been an accumulation of modifications upon modifications in the course of an unknown descent of one organism from another. Why did these modifications stop short of the production of a species or of several species in which no resemblance of parts more or less functionally useful could be found? The supposition is that the modifications have been going on through millions of years. Time enough, therefore, has elapsed for the destruction of all uniformity of structure; and the causes of modification are as immeasurable as the period through which they are supposed to have been operating. The imaginary ancestral stock, wherever it is placed in the line of remote descent, had, in its first distinctive existence, a peculiar structure, which it bequeaths to its offspring. In the countless generations of its descendants, modifications of that structure take place, until a new animal is evolved. What preserved any unity of type from the modifying influences? It was not choice on the part of the several descending species; not a conscious exertion to preserve something; it was nothing but the propinquity of descent, which by the law of heredity transmitted certain resemblances. But why was that law so potent that it could preserve a certain unity of type, and at the same time so powerless as not to prevent the modifications which the successive organisms have undergone in all other respects? Or, to reverse the terms of the question, why were the causes of modification sufficiently powerful to produce distinct species, and yet not powerful enough to eliminate the resemblances which we find obtaining throughout the whole group of animals to which these several species belong? It would seem that here we are not to lose sight of the fact that, in the animal kingdom, procreation never takes place between a male and a female of distinct species, and that we have no reason to believe that it ever did take place.