If we compare the recently published fourth edition of Haeckel’s _Anthropogeny_, 1891, and the eighth edition of his _History of Creation_, with the early editions, we cannot help remarking, with considerable astonishment, despite the enormous increase of fresh material, the fact that little in the old plans and principles of the work needs correction. Even the bold generalisations, the inference as to the identity of form of the original beginnings of all of the middle or higher classes of animals, the “Gastræa Theory” of Haeckel, at first so violently opposed, the stress laid upon the equivalence of the blastoderms in the various orders of animals, nay, even many of the animal genealogies, really only asserted as a working hypothesis, have stood the test beyond all expectation; although Du Bois-Reymond insinuated that the pedigrees of the heroes of Homer were more worthy of credit. To appreciate the complete victory of these ideas one need but refer to the discourse _On Recapitulation in Embryology_ with which A. Milnes Marshall opened the meeting of the Biological Section of the British Natural History Society at Leeds, September, 1890. The very conspicuous irregularities in the formation of organised bodies, which formerly were regarded as monstrosities, or as the freaks and riddles of the formative instinct, the hare-lips, the cleft palates, cases of microcephaly, etc., or the conspicuous want of symmetry in the physical structure of the plaice and sole, formerly made use of by Mivart and Schimper as unassailable counterproofs of Darwin’s doctrines, have shaped themselves into the most decisive verifications of his theory; as in fact, generally, a number of the most splendid evidences of the correctness of the theory have, as the result of exact investigations in organic evolution, proceeded from the most obstinate of its supposed difficulties. Thus, for example, as proof that birds are far removed from the other classes of vertebrates, the circumstance had been cited that certain parts connected with the visual organs are in them situated at the side of the brain, instead of on the dorsal surface, as is the case with the other vertebrates. But a more exact observation has shown that this variation in formation is a secondary result, since in each previous period of development these same organs in the young birds lie, exactly as in the case of the other vertebrates, on the dorsal surface, and only shortly before leaving the egg do they move downward to the sides. In many cases where the development of parts preservable in fossil conditions is under consideration, as for instance portions of the skeleton, the hard integuments, and the teeth, a direct proof may, by comparison, be furnished of the truth of the fact of the correspondence of the embryological formations of living animals with the final and permanent forms of their extinct representatives, a fact which was indeed acknowledged by Agassiz and Vogt, but completely misunderstood.