[44] A full account of the present state of the subject will be found in Morgan’s Experimental Zoology, New York, 1907.
[45] But there certainly exist many formative relations between the real sexual organs and the so-called secondary sexual characters. Herbst has given a full analytical discussion of all that is known on this subject; but the facts are much more complicated than is generally supposed, and do not lend themselves therefore to short description. See also Foges, Pflüger’s Arch. 93, 1902.
[46] It seems that in some cases (Dinophilus, certain Arthropods) the sexual products are invariably determined as “arrenogennetic” or as “thelygennetic” (Wilson, Journ. Exp. Zool. ii. and iii. 1905–6), whilst in others (Amphibia) the state of maturation or “super”-maturation determines the sex of the future organism (R. Hertwig, Verh. D. Zool. Ges. 1905–7).
[47] Driesch, Die organischen Regulationen, Leipzig, 1901; Morgan, Regeneration, New York, 1901.
[48] But real compensatory differentiation occurs in the cases of so-called “hypertypy” as first discovered by Przibram and afterwards studied by Zeleny: here the two organs of a pair show a different degree of differentiation. Whenever the more specialised organ is removed the less developed one assumes its form. Similar cases, which might simply be called “compensatory heterotypy,” are known in plants, though only relating to the actual fate of undifferentiated “Anlagen” in these organisms. A leaf may be formed out of the Anlage of a scale, if all the leaves are cut off, and so on.
[49] For a fuller analysis compare my opening address delivered before the section of “Experimental Zoology” at the Seventh Zoological Congress, Boston, 1907: “The Stimuli of Restitutions” (see Proceedings of that Congress).
[50] The problem of the stimulus of a secondary restitution as a whole must not be confused with the very different question, what the single “formative stimuli” concerned in the performance of a certain restitutive act may be. With regard to restitution as a whole these single “formative stimuli” might properly be said to belong to its “internal means”—in the widest sense of the word.
[51] T. H. Morgan is very right in stating that, in regeneration, the “obstacle” itself is newly formed by the mere process of healing, previous to all restitution, and that true restitution happens all the same.
[52] I merely mention here the still “simpler” one—applicable of course to regeneration proper exclusively—that for the simple reason of being “wounded,” i.e. being a surface open to the medium, the “wound” brings forth all that is necessary to complete the organism.
[53] That compensatory hypertrophy cannot be due to “functional adaptation”—to be analysed later on—was proved by an experiment of Ribbert’s. Compensation may occur before the function has made its appearance, as was shown to be the case in the testicles and mammae of rabbits. (Arch. Entw. Mech. 1, 1894, p. 69.)