There is no doubt that profounder researches in evolutionary history will furnish still more important results: for instance, the more perfect elucidation of the pedigree of mammals; for in this province even our domestic animals are not sufficiently investigated. Every new effort in this direction, for example the recent work of Klever on the evolution of the teeth of the horse, and other investigations concerning the formation of special organs, has invariably shown that much in this field yet remains to be discovered. We have only to recall to mind the recent investigations relating to the development of the pineal gland, which in the last decennium have also led to the discovery of a rudimentary occipital eye, which seems to have actually existed and performed functions in numerous early representatives of the vertebrates, but to-day is simply a fact of history, and has given rise to an organ which Descartes considered as the seat of the soul. We may here also refer to the recent investigations concerning the earlier developmental stages of the duckbills, which have completely confirmed what the theory asserted in advance and required; namely, that they fill the vacancy between the egg-laying reptiles and the mammalia which bring forth their young alive. Only a few years ago Carl Vogt vehemently opposed the opinion of the duckbills being transitional types, and sought to explain their inferior stage of organisation, which is also evidenced in their low blood temperature, as the results of a stunting process (degeneration, so called). They formed a degenerated branch of marsupials, nothing more. Later, the remarkable yet long anticipated fact was revealed by Haacke and Caldwell, 1884, that the duckbills are egg-laying mammals, a character which certainly could not have been acquired through degeneration, but which simply shows that they are closely related to extinct reptilian forms. In one other respect, namely, with regard to their supply of teeth, the process of degeneration must indeed be admitted. On this point, Poulton and Thomas discovered a few years ago that in their early stages they really do possess true teeth, which, however, just as in the case of certain carnivorous cetacea, later completely disappear, and are replaced by a sort of horny teeth. This, however, is really not a true degeneration, but rather a special adaptation, doubtless beneficial to the animal in some way or other; and with as little reason as we may regard birds as a degenerated race in comparison with their progenitors, because they have lost the numerous teeth which these possessed, with just as little reason can we hold that the duckbills, in their general organisation, have suffered any retrogression worth mentioning. On the contrary, the recent investigations of Marsh and Lemoine concerning the mammals of the Jurassic and Cretaceous periods point more and more distinctly to the conclusion, that there existed among these mammals a very large