404 SCIENCE PROGRESS 



to satisfy Dr. Bateson by saying that, as in ordinary toads so 

 in the modified Alytes, the horny pad was only developed in 

 the breeding season, and was a temporary phenomenon. He 

 said that in this, as in other experiments, he had had to decide 

 whether to retain his specimens alive for further work, or to 

 sacrifice them in order to satisfy objectors, and that he had 

 decided on the former course. 



Since publishing this paper, however, Kammerer has sent 

 sections through the skin of the hand of the abnormal Alytes to 

 Dr. Bateson, and these Dr. Bateson has been good enough to 

 show to the author of the present article, and in these sections 

 the horny pad with its prickles can be clearly made out. 



It will occur to the reader that it is of cardinal importance 

 to the theory of heredity that these experiments should be 

 repeated, and indeed it was partly with the hope of stimulating 

 naturahsts everywhere to undertake this task that this article 

 was written. But the difiiculty of such work should be clearly 

 realised. It is necessary to find an animal that will respond to 

 a change of environment by a change of habit or structure, 

 and this is by no means easy. If, however, this difficulty is 

 surmounted, and the animal is reared to maturity under the 

 new conditions, and is induced to breed, then the young have to be 

 divided into two lots, one portion being allowed to remain under 

 the new conditions, and the other portion restored to the old 

 conditions. It most frequently happens that those offspring 

 which are thus replaced in the ancestral environment lose the 

 modification produced by the new conditions, and this is often 

 triumphantly referred to by Mendelians as a proof that the 

 modification was merely " somatic," and not " germinal. 

 But this reasoning is fallacious. If the constitution of the 

 animal is so labile that a change from condition A to condition 

 B produces a certain modification, the reverse change from 

 condition B to condition A should undo it. The utmost that 

 we could expect to find — and what, indeed, Kammerer claims 

 to have found in his salamander experiments — is that the 

 offspring of the modified parents, when replaced in ancestral 

 conditions, should in their early development still show traces 

 of the modification (this is the essence of " recapitulation "), 

 and that young exposed to the further action of the changed 

 environment should exhibit the modification in an intensified 

 degree. 



In the Zoological Gardens in London attempts are being 

 made to repeat Kammerer's experiments with the salamander. 

 These experiments were begun a year ago, but we must wait 

 between two and three years before the young exposed to the 

 altered conditions become sexually ripe, and three or four years 

 must elapse subsequent to this event before it is possible to 



