That is the first of our important negative statements about regulations; the second relates to the phrase just used, “or it does not occur at all.” There are indeed limits of regulability; adaptations are not possible to every sort of change of the physiological state: sickness and death could not exist if they were; nor is restitution possible in all cases where it might be useful. It is a well-known fact, that man is only able to heal wounds but is altogether destitute of the faculty of regeneration proper. But even lower animals may be without this faculty, as are the ctenophores and the nematodes for instance, and there is no sort of correspondence between the faculty of restitution and the place in the animal kingdom. It is not altogether impossible that there may be found, some day, certain conditions under which every organism is capable of restoring any missing part; but at present we know absolutely nothing about such conditions.[120]
But no amount of negative instances can disprove an existing positive—which is what we have been studying. Our analysis based upon the existence of regulations is as little disparaged by cases where no regulability exists as optical studies are by the fact that they cannot be undertaken in absolute darkness.
D. INHERITANCE: SECOND PROOF OF THE AUTONOMY OF LIFE
All organisms are endowed with the faculty of re-creating their own initial form of existence.
In words similar to these Alexander Goette, it seems to me, has given the shortest and the best expression of the fact of inheritance. Indeed, if the initial form in all its essentials is re-created, it follows from the principle of univocality, that, ceteris paribus, it will behave again as it did when last it existed.
By the fact of inheritance life becomes a rhythmic phenomenon, that is to say, a phenomenon, or better, a chain of phenomena, whose single links reappear at constant intervals, if the outer conditions are not changed.
The Material Continuity in Inheritance
It was first stated by Gustav Jaeger and afterwards worked out into a regular theory by Weismann, that there is a continuity of material underlying inheritance. Taken in its literal meaning this statement is obviously self-evident, though none the less important on that account. For as all life is manifested on bodies, that is on matter, and as the development of all offspring starts from parts of the parent bodies, that is from the matter or material of the parents, it follows that in some sense there is a sort of continuity of material as long as there is life—at least in the forms we know of. The theory of the continuity of “germ-plasm” therefore would be true, even if germ-cells were produced by any and every part of the organism. That, as we know, is not actually the case: germ-cells, at least in the higher animals and in plants, are produced at certain specific localities of the organism only, and it is with regard to this fact that the so-called theory of the “continuity of germ-plasm” acquires its narrower and proper sense. There are distinct and specific lines of cell-lineage in ontogenesis, so the theory states, along which the continuity of germ-protoplasm is kept up, which, in other words, lead from one egg to the other, whilst almost all other lines of cell-lineage end in “somatic” cells, which are doomed to death. What has been stated here is a fact in many cases of descriptive embryology, though it can hardly be said to be more than that. We know already, from our analytical and experimental study of morphogenesis, that Weismann himself had to add a number of subsidiary hypotheses to his original theory to account for the mere facts of regeneration proper and the so-called vegetative reproduction in plants and in some animals, and we have learned that newly discovered facts necessitate still more appendixes to the original theory. In spite of that, I regard it as very important that the fact of the continuity of some material as one of the foundations of inheritance has clearly been stated, even if the specialised form of the theory, as advocated by Weismann in the doctrine of the “germ-lineages” (“Keimbahnen”) should prove unable to stand against the facts.