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This book was written in defense of the thesis that acquired characteristics may be inherited. In the first or biologic part, Kammerer first reviews the work of others. He accepts the conclusions of his predecessors that color changes produced in butterflies by exposure to heat or cold are transmitted to the progeny, although he admits that the conditions of the experiments were such that the possibility of direct influence on the germ plasm could not be ruled out. Likewise he accepts the validity of the conclusions on the effect of heat and aridity on beetles in producing changes that are passed on to succeeding generations, although it is possible that the acquired characteristics are not really new but are the resurrection of old ones.
Kammerer's own experiments were designed to avoid the charge both of "parallel induction" and of "atavism." For this purpose he chose the spotted salamander. By keeping