This amended formula now reads: The development of germs is an abridgment of the development of stems, and is the more complete according as the development of the abridgment is continued by inheritance, the less complete according as the development of the false is introduced by adaptation. Now, we ask: Is this biogenetic maxim correct? and moreover, from the fact of the organic individuals originating through development, are we entitled to draw the conclusion that even the species must have originated through development? To this question we can no longer get an answer from the life-processes of living organisms; for we have already mentioned the fact that, according to the present state of our knowledge, we can no longer observe the origination of a new species. Moreover, the embryonic states of development show also, in all their similarity, even in the very first stages, and with especial distinctness in these first stages, many differences between the single species; and this is true especially of those species which, according to the followers of this so-called biogenetic maxim, should lie in the same stem-line,--so that the direct scientific value of the embryological results to the palaeontological investigation, or of the latter to the former, is so far very slight. Such a problem, however, as the one contained in that biogenetic maxim, which only gives to investigators the _direction_ in which possibly an {81} interesting and profitable path can be opened, does not at all deserve the name of a "_law_." K. E. von Baer, the founder of the whole present science of the history of development, has certainly a most competent judgment of the correctness of this so-called biogenetic maxim; and he convincingly shows, in his essay on "Darwin's Doctrine," that the embryos never represent a former animalic form, but that their development follows the principle of representing first the common characteristics of the class, then those of the order, etc., until finally the individual characteristics appear in the formation. Those who wish more information about embryology can find it in Heinrich Rathke's "Entwicklungsgeschichte der Wirbelthiere" ("History of the Development of Vertebrates"), edited by A. Koelliker, Leipzig, Engelmann, 1861; and those who wish to inform themselves as to the influence of the ontogenetic results of the solution of the phylogenetic problems, will find, besides the before-mentioned work of Wigand, rich and clearly elaborated material in the publication of Wilhelm His--"Unsere Koerperform und das physiologische Problem ihrer Entstehung, Briefe an einen befreundeten Naturforscher" ("The Form of our Body and the Physiological Problem of its Origin; Letters to an Associate Scientist"), Leipzig, Vogel, 1875. The latter writer, although he advocates the descent theory, rejects the hasty assertions of Haeckel with direct and convincing arguments.