M. Pruner Bey, resuming the descriptive and anatomical works which have been carried on till within the last few years, has shown that the comparison of man with the anthropomorphous apes brings to light a fact which is subject to very few exceptions, the existence, namely, of an _inverse order_ in the development of the principal organs. The researches of Welker upon the sphenoïdal angle of Virchow lead to the same conclusion, for in man the angle diminishes from the time of birth, whilst in the ape it is always increasing, so much so that sometimes it is effaced. It is upon the base of the cranium that the German anatomist has remarked this inverse order, the importance of which cannot escape notice. A similar contrast has been remarked by Gratiolet upon the brain itself. The following are his observations upon this subject. In the ape the temporal sphenoïdal convolutions, which form the middle lobe, make their appearance and are completed before the anterior convolutions which form the frontal lobe. In man, on the contrary, the frontal convolutions are the first to appear, and those of the middle lobe are formed later. It is evident, especially after the most fundamental principles of Darwinism, that an organised being cannot be a descendant of another whose development is in an inverse order to its own. Consequently, in accordance with these principles, man cannot be considered as the descendant of any simian type whatever. VII. I have said above that palæontology has never shown anything which recalls in the slightest degree the hypothetical _pithecoid man_ of Haeckel. A hope was felt that what could not be found among extinct forms might be found among living ones. Vogt has compared the brain of microcephali to that of the anthropomorphous apes, and Haeckel has represented in his genealogical table of idiots, crétins and microcephali as actual representatives of his _speechless man_. These beings, with their small brain and incomplete faculties, are, according to these two naturalists, cases of _atavism_, and recall the normal state of our most remote direct ancestors. Here we have another instance of the curious method of reasoning familiar to Darwinists. Microcephalism, idiotcy, and crétinism constitute so many teratological or pathological states. They belong, consequently, to the very numerous groups of facts which have long been studied. If some of these facts can be regarded as _phenomena of atavism_, why should it be otherwise with the rest? Why attribute to atavism a single character only in crétins and microcephali, and refer the other to teratology and pathology? This is evidently an _entirely arbitrary_ kind of treatment, and as much opposed as possible to the true scientific method.