_De Vries_ proves that certain variations appear suddenly and without any known cause, and have a much greater tendency to be preserved than the variations obtained by crossing and selection. In my opinion the phenomena of the mneme revealed by _Hering_ and _Semon_ explain the apparent contradictions which have hitherto impaired the theories of heredity. Mnemic engraphy explains, by its infinitesimal and repeated action through numerous generations, how the external world may little by little transmit to the germinal cells the characters which it impresses on organisms. The eight hundred generations during which the prepuce of the Jews has been cut off have not yet sufficed for the ecphoria of the corresponding negative mnemic engraphia; while conjugation and selection modify rapidly and strongly in a few generations; a fact which is more striking and allows of direct experiment. Moreover, a positive engraphia must necessarily act more powerfully, and it seems to me that mutations must be the ecphoria of accumulated former latent engraphias. _Merrifield_ and _Standfuss_, by exposing caterpillars and chrysalids for varying periods to considerable degrees of cold and heat, have determined permanent changes in the specific characters of the butterflies which have emerged from them. _Standfuss_ and _Fischer_ have also shown that, after several generations, by continuing the action of cold on the caterpillars, the variations thus produced can be preserved even after the cold has ceased to act. No doubt the cold acts on the germinal cells as on the rest of the body, but the heredity of an acquired character is thus demonstrated. The experiments of _Miss de Chauvin_ on salamanders (_Axolotl_) are still more conclusive, for we are dealing here with characters acquired through aquatic or aërial media, which can hardly act on the sexual glands. We cannot continue this subject any further and we return to the work of _Semon_. It is needless to say that the nature of mnemic engraphia remains itself an unknown quantity. As long as we are unable to transform inert matter into a living organism we shall remain in ignorance. But, when it is accepted with the laws of the phenomena which it produces, this unknown quantity, as _Semon_ has shown, alone suffices to explain all the rest, and is already a great step toward the comprehension of the laws which govern life. =Blastophthoria.=--By blastophthoria, or deterioration of the germ, I mean what might also be called false heredity, that is to say, the results of all direct pathogenic or disturbing action, especially that of certain intoxications, on the germinal cells, whose hereditary determinants are thus changed. Blastophthoria thus acts on germs not yet conjugated, through the medium of their bearers, and creates at their origin _hereditary stigmata_ of all kinds, while true heredity only combines and reproduces the ancestral energies.