. The dynamics of living matter. Reproduction; Regeneration (Biology); Biochemistry; Reproduction; Biochemistry. DYNAMICS OF REGENERATIVE PROCESSES 221 Giard and Caullery, as well as the experiments of Driesch, resemble those in Campanularia, and Driesch also expresses the opinion that this is a case of reversibility of the processes of development. The idea that the process of development is in certain forms reversi- ble is also supported by the experiments of Frank Lilhe on fresh-water Planarians. Lilhe found that adult fresh- water Planarians if exposed to starvation not only become gradual
. The dynamics of living matter. Reproduction; Regeneration (Biology); Biochemistry; Reproduction; Biochemistry. DYNAMICS OF REGENERATIVE PROCESSES 221 Giard and Caullery, as well as the experiments of Driesch, resemble those in Campanularia, and Driesch also expresses the opinion that this is a case of reversibility of the processes of development. The idea that the process of development is in certain forms reversi- ble is also supported by the experiments of Frank Lilhe on fresh-water Planarians. Lilhe found that adult fresh- water Planarians if exposed to starvation not only become gradually smaller in size but ultimately return to an embryonic form! These experiments have been repeated and confirmed by Schultze. There is a possibility that a definite kind of chemical substances must be present in order to make development, regeneration, and growth possible. Such tissues as contain these substances (or mixture of substances) may be called embryonic. If this idea be correct, and if it be true that phenomena of development are reversible, — to a great extent in a few forms, and to some extent perhaps generally, — the question might be raised whether or not one of the conditions of regeneration is the transformation of adult tissue into more embryonic tissue. If this were true, the power of regeneration of an organism might depend upon the degree of reversibility of the processes of development in such a form. It is certainly in harmony with such an idea that forms like Hydroids, Ascidians, and fresh-water Planarians, where the reversibility of the process of development is most outspoken, possess also the greatest power of regeneration among animals. The idea suggested is further supported by the fact that the power of regeneration by the embryo is often considerably greater than the power of regeneration of the same form in the adult stage. The tadpole of a frog is capable of regenerat- ing a leg, while this is impossible in the adult frog. This removes ^the
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