4. _Embryonic Development._--From the human ovule, which is said to differ in no respect from the ovule of other animals, into and through the early embryonic period, we are told that the embryo of man can hardly be distinguished from that of other members of the vertebrate kingdom. It is not necessary to repeat the details of the resemblance, which are undoubtedly striking, because they show a remarkable similarity between the embryo of man and that of the dog and the ape, in the earlier stage of the development, and that it is not until quite in the later stages of development that the three depart from each other, the difference between the young human being and the ape being not so great as that between the ape and the dog. We may, of course, accept Prof. Huxley's testimony that "the mode of origin [conception?] and the early stages of the development of man are identical with those of the animals immediately below him in the scale; without a doubt, in these respects, he is far nearer to the apes than the apes are to the dog."[48] 5. _Rudiments._--This is a somewhat obscure branch of the proofs, which requires a more detailed examination in order to appreciate its bearing on the general theory of evolution. A distinction is made between rudimentary and nascent organs. The former are absolutely useless to their possessor--such as the mammæ of male quadrupeds, or the incisor teeth of ruminants, which never cut through the gums--or else they are of such slight service to their present possessors that they can not be supposed to have been developed under the conditions which now exist. These useless, or very slightly useful, organs in the human frame, are supposed to have been organs which had an important utility in the lower animals from which man is descended, but, by disuse at that period of life when the organ is chiefly used, and by inheritance at a corresponding period of life, they became of less and less utility in the successive animals that were evolved out of the preceding forms, until they sank into the condition of useless appendages, although perpetuated by force of the derivation of one species of animal from another, caused by the operation of the laws of natural and sexual selection. Nascent organs, on the other hand, are those which, though not fully developed to their entire capability, are of high service to their possessor, and may be carried to a higher degree of utility. One of the characteristics, as it is said, of rudimentary organs, is that they often become wholly suppressed in individuals, and then reappear occasionally in other individuals, through what is called reversion, or a return to ancestral peculiarities.[49] We are told that "not one of the higher animals can be named which does not bear some part in a rudimentary condition; and man forms no exception to the rule."[50]