shorter and shorter time, new acquisitions are being more and more highly developed, and thus, in the course of the phylogeny, numerous time-displacements of the parts and organs in ontogeny must result, so that ultimately it is impossible to compare a particular stage in the embryogenesis of a species with a particular ancestral form. _Only the stages of individual organs can be thus compared and parallelized._ But we must not on that account 'empty out the child with the bath,' and conclude that there is no such thing as a 'biogenetic law' or recapitulation of the phylogeny in the ontogeny. Not only is there such a recapitulation, but--as F. Müller and Haeckel have already said--ontogeny is nothing but a recapitulation of the phylogeny, only with innumerable subtractions and interpolations, additions and displacements of the organ-stages both in time and place. It would be a great mistake to conclude from the fact of these manifold alterations that the whole proposition of the recapitulation of the phylogeny in the ontogeny is erroneous, or at least valueless. If its only use were to enable us to read the racial history of a species out of its germinal history, it is intelligible enough that we might be led to give it up in despair, but I think that the main thing is to get some insight into the history of the ontogeny, and there can be no doubt that this can have been built up on no other foundation than upon the racial history. What is new could only have arisen from what was already in existence, and everything in ontogeny, not only the palingenetic stages which still represent in some measure the facies of fully-formed ancestral stages, but also the cœnogenetic stages, like the pupa-stage we have already discussed, have arisen historically, nothing _de novo_, but all in connexion with what was already present. But what was first present was in all cases the stages of the ancestral forms.