INHERITANCE OF ACQUIRED CHARACTERS 47 



by Darwin. In the light of careful experiment, however, it has been 

 largely discredited. The verdict of "not proven" has been pro- 

 nounced against it, and many biologists would go even further and 

 claim with T. H. Morgan that the theory was " unnecessary." Yet, 

 not content with such a verdict, a small number of workers have per- 

 sisted in their attempts to establish the theory of acquired characters 

 as one of the essential factors of evolution. 



Eecently the discussions of evolution have begun to take a new turn. 

 The old attempt to find one single all-important factor is being aban- 

 doned for a broader point of view that allows the possibility of many 

 factors, some of them perhaps still unknown. V. L. Kellogg has 

 pointed out the smallness of the number of observed mutations on which 

 to base a comprehensive theory. Castle, a strong believer in mutation 

 and unit characters, has affirmed his belief in the efficacy of selection in 

 the production of new forms. Nowhere in the literature of the last 

 year or two can be found any very dogmatic claim for a single all- 

 important factor which will serve as the basis for all kinds of evolution. 



In this new atmosphere Lamarck's theory again receives serious 

 attention, but not in its old form. To-day no one ventures to cite such 

 examples as Spencer's famous illustration of the puppy that inherited 

 from its mother the trick of begging for food. Such experiments as 

 breeding away the wings of flies in small tubes, or breeding away the 

 eyes of flies in dark chambers, attract but little attention. No great 

 biologist is giving much time to experiments testing the inheritance of 

 mutilations. On the other hand, there are many experiments to test 

 the inherited effect of starvation, to test the effect of the application of 

 chemicals directly to the germ plasm, and to test the effect of the appli- 

 cation of extremes of temperature to animals with ripe germ cells. 

 Several investigators have shrewdly seen the value of working with 

 plastic types of animals like the amphibians, which present striking 

 examples of dimorphism such as are found in axolotyl, Diemyctylus 

 and various frog tadpoles. In this field a prominent worker is Kam- 

 merer, a representative of a school of experimental evolution in Vienna. 



A short summary will be given of his researches on toads, tree frogs 

 and salamanders. A few selected experiments will show very well the 

 nature of the most recent work on the inheritance of acquired characters. 



Kammerer in his work on the toad, Alytes, tried to prolong the 

 tadpole stage until sexual maturity. He exposed the young tadpoles 

 to a number of conditions such as darkness, cold, perfectly still water, 

 each of which acting by itself tended to prolong the larval period. By 

 exposing tadpoles to all of these conditions acting at the same time, he 

 succeeded in producing one sexually mature female with the usual 

 form of a tadpole but with mouth, legs and sexual organs of an adult 

 toad. This one example was mated to a normal male. The progeny 



