[151] Of course the inheritance of specific values from the results of fluctuating variations, leading to new averages of variability (see p. 265), may also be understood in this manner, the conditions of nourishment acting upon the adult and upon its germs equally well. [152] *Berichte üb. d. Sitzung. d. Ges. f. Bot.*, Hamburg, 1887, 3 Heft. Would it not be possible at least that adaptations which last for thousands of generations or more might in fact change the adaptive character into a congenital one? Then we not only should have inheritance of acquired characters, but should have a sort of explanation at the same time for the remarkable fact that certain histological structures of a very adapted kind are formed ontogenetically before any function exists, as is known to be the case with the structures in the bones of vertebrates, for instance. Experiments are going on at Paris, and perhaps in other places of scientific research also, which, it is hoped, will show that animals reared in absolute darkness for many generations will lose their perfectly formed eyes, and that animals from the dark with very rudimentary eyes will be endowed with properly functioning ones, after they have been reared in the light for generations. Such a result indeed would account for the many animals, of the most different groups, which live in dark caves and possess only rudiments of eyes: functional adaptation is no longer necessary, so-called atrophy by inactivity sets in, and the results “acquired” by it are inherited.[153] [153] Quite recently Kammerer (*Arch. Entw. Mech.* 25, 1907, p. 7) has published very important experiments on the inheritance of “acquired” modifications with regard to the peculiarities of reproduction in *Salamandra atra* and *S. maculosa*. It seems rather improbable--though not absolutely impossible--that the germ cells were directly affected by the external modifying agent in this case. But enough of possibilities. Let us be content at present to know at least a few real instances with regard to the slowness of the process of what might be said to be “re-adaptation” in some plants. This process shows us a way by which our problem may some day be solved; it allows us to introduce inheritance of acquired characters as a legitimate hypothesis at least, which not only will explain many of the diversities in systematics historically, but also can be called, though not a *causa vera*, yet certainly more than a mere fiction. OTHER PRINCIPLES WANTED