[54] At any given time only the absolute size of the regenerated part is greater in animals which are well fed; the degree of differentiation is the same in all. Zeleny has found that, if all five arms of a starfish are removed, each one of them will regenerate more material in a given time than it would have done if it alone had been removed. But these differences also only relate to absolute size and not to the degree of differentiation. They possibly may be due in fact to conditions of nourishment, but even here other explanations seems possible (Zeleny, Journ. exp. Zool. 2, 1905).
[55] For a good discussion of “super-regeneration” in the roots of plants see Němec, Studien über die Regeneration, Berlin, 1905. Goebel and Winkler have succeeded in provoking the “restitution” of parts which were not removed at all by simply stopping their functions (leaves of certain plants were covered with plaster, etc.). (Biol. Centralbl. 22, 1902, p. 385; Ber. Bot. Ges. 20, 1902, p. 81.) A fine experiment is due to Miehe. The alga Cladophora was subjected to “plasmolysis,” each cell then formed a new membrane of its own around the smaller volume of its protoplasm; after that the plants were brought back to a medium of normal osmotic pressure, and then each single cell grew up into a little plant (all of them being of the same polarity!). Two questions seem to be answered by this fact: loss of communication is of fundamental importance to restitution, and the removal of mechanical obstacles plays no part in it, for the mechanical resistances were the same at the end of the experiment as they had been at the beginning. (Ber. Bot. Ges. 23, 1905, p. 257.) For fuller analysis of all the problems of this chapter see my Organische Regulationen, my reviews in the Ergebnisse der Anatomie und Entwickelungsgeschichte, vols. viii. xi. xiv., and my Boston address mentioned above. Compare also Fitting, Ergebn. d. Physiol. vols. iv. and v.
[56] The so-called “inner secretion” in physiology proper would offer a certain analogy to the facts assumed by such an hypothesis. Compare the excellent summary given by E. Starling at the seventy-eighth meeting of the German “Naturforscherversammlung,” Stuttgart, 1906.
[57] The name of singular-equipotential systems might also be applied to elementary organs, the single potencies of which are awaked to organogenesis by specific formative stimuli from without; but that is not the case in the systems studied in this chapter.
[58] The distance of the other boundary line from a or b would be given by the value of s.
[59] A far more thorough analysis of this differentiation has been attempted in my paper, “Die Localisation morphogenetischer Vorgänge. Ein Beweis vitalistischen Geschehens,” Leipzig, 1899.
[60] This statement is not strictly correct for Tubularia. I found (Archiv f. Entwickelungsmechanik, ix. 1899), that a reduction of the length of the stem is always followed by a reduction of the size of the hydranth-primordium, but there is no real proportionality between them. It is only for theoretical simplification that a strict proportionality is assumed here, both in the text and the diagram. But there is an almost strict proportionality in all cases of “closed forms.”
[61] One might object here that in a piece of a Tubularia stem, for instance, the tissues are in direct contact with the sea-water at the two points of the wounds only, and that at these very points a stimulus might be set up—say by a process of diffusion—which gradually decreases in intensity on its way inward. And a similar argument might apply to the small but whole blastula of Echinus, and to all other cases. But, in the first place, stimuli which only differ in intensity could hardly call forth the typical and typically localised single features realised in differentiation. On the other hand—and this will overthrow such an hypothesis completely—the dependence of the single localised effects in every case on the absolute size of the fragment or piece chosen for restoration renders quite impossible the assumption that all the singularities in the differentiation of the harmonious systems might be called forth by single stimuli originating in two fixed places in an independent way. These would never result in any “harmonious,” any proportionate structure, but a structure of the “normal” proportionality and size at its two ends and non-existent in the middle!
[62] See my article in Biolog. Centralblatt, 27, 1907, p. 69. The question is rendered still more complicated by the fact that in the case of the regeneration, say, of a leg it is not the original “morphogenetic compound” which is again required for disintegration, after it has become disintegrated once already, but only a specific part of it: just that part of it which is necessary for producing the leg! On the other hand, it would be impossible to understand, on the basis of physical chemistry, how the isolated branchial apparatus of Clavellina could be transformed, by chemical processes exclusively, into a system of which only a certain part consists of that substance of which the starting-point had been composed in its completeness.
[63] Besides the specified poles determined by the polar-bilateral structure of the protoplasm.