The systematists who have made a special study of Batrachia appear to be agreed that Alytes in nature does not have these structures; and when individuals possessing them can be produced for inspec­tion it will, I think, be time to examine the evidence for the inheritance of acquired characters more seriously. I wrote to Dr. Kammerer in July, 1910, asking him for the loan of such a specimen and on visiting the Biologische Versuchsanstalt in September of the same year I made the same request, but hitherto none has been produced. In matters of this kind much generally depends on interpreta­tions made at the time of observa­tion; here, however, is an example which could readily be attested by preserved material.[288]

More recently the same author has reported another hereditary morpho­logical change brought about by outside condi­tions.[289] A certain salamander (Salamandra maculosa) has yellow spots on a generally dark skin. Kammerer states that if such salamanders are kept on a yellow ground they become more yellow, not by an extension of the chromatophores (which would not be surprising) but by actual multiplica­tion and growth of the yellow pigment cells; while the black skin is inhibited in its growth. The reverse is true if these salamanders are kept on black soil; in this case according to Kammerer the growth of the yellow cells of the skin is inhibited while the black part of the skin grows. Curiously enough, according to him, these induced changes are hereditary. Here again we are dealing with the inheritance of an acquired morpho­logical character.

Megusar[290] has repeated Kammerer’s experi­ments on salamanders but contradicts him by stating that the colour of the soil has no influence on the coloura­tion of salamanders. Of course, we know the phenomenon of colour adapta­tion in which the animal changes its colour pattern according to the environ­ment. This is an effect of the retina image on the skin and has been interpreted by the writer as a case of colour telephotography, for which no physical explana­tion has yet been found.[291] This phenomenon, however, does not lead to any hereditary change of colour.

Kammerer makes many statements on the heredity of acquired modifica­tions of instinct; indeed he claims that an interest in music on the part of parents produces offspring with musical talent. In such claims much depends upon the subjective interpreta­tion of the observer.

The writer is not aware that there is at present on record a single adequate proof of the heredity of an acquired character. We have records of changes in the offspring by poisoning the germ plasm by alcohol given to parents—as in Stockard’s well-known experi­ments—or by exposing butterflies to extreme temperatures, but in these cases the germ cells were poisoned or altered by the alcohol or by chemical compounds produced at very low or very high temperatures. This is of course an entirely different thing from stating that by inducing the midwife toad to lay its eggs in the water the male offspring acquires the pads and horns of other species of frogs on its thumb; or that by keeping black salamanders on yellow paper the offspring is more yellow. Yet if there is an inheritance of acquired characters which can in any way throw light on the so-called phenomena of adapta­tion it must consist in results such as Kammerer claims to have obtained.

While the writer does not decline to accept Ehrlich’s interpreta­tion of the arsenic-fast strains of trypanosomes or Kammerer’s statements in regard to the inheritance of acquired character, he feels that more work should be done before they can be used for our problem.

7. This attitude leaves us in a quandary. The whole animated world is seemingly a symphony of adapta­tion. We have mentioned already the eye with its refractive media so well curved and placed that a more or less perfect image of the outside objects is focussed exactly on the retina; and this in spite of the fact that lens and retina develop independently; we have mentioned and discussed the cases of instincts or automatic arrangements which are required to perpetuate life—the attrac­tion of the two sexes and the automatic mechanisms by which sperm and egg are brought together; the maternal instincts by which the young are taken care of; and all those adapta­tions by which animals get their food and the suitable condi­tions of preserva­tion. Can we understand all these adapta­tions, without a belief in the heredity of acquired characters? As a matter of fact the tenacity with which some authors cling to such a belief is dictated by the idea that this is the only alternative to the supra-naturalistic or vitalistic ideas. The writer is of the opinion that we do not need to depend upon the assump­tion of the heredity of acquired characters, but that physio­logical chemistry is adequate for this purpose.

The earlier writers explained the growth of the legs in the tadpole of the frog or toad as a case of an adapta­tion to life on land. We know through Gudernatsch that the growth of the legs can be produced at any time even in the youngest tadpole, which is unable to live on the land, by feeding the animal with the thyroid gland. As we have stated in Chapter VII, it is quite possible that in nature the legs of the tadpole begin to grow when enough of the thyroid or a similar compound has been formed or is circulating in the animal.

It might justly be claimed as a case of adapta­tion that the egg attaches itself to the wall of the uterus and calls forth the forma­tion of the decidua. We have mentioned the observa­tion of Leo Loeb that the corpus luteum of the ovary gives off a substance to the blood which alters the tissues in the uterus in such a way that contact with any foreign body (e. g., the egg) induces this decidua forma­tion. Again what appeared as adapta­tion when unknown turns out to be a result of the action of a definite chemical substance circulating in the body.