456 



THE AMERICAN NATURALIST 



[Vor,L 



mutation is limited to certain lines and (d) that experi- 

 mental evolution seems chiefly due to dropping out of 

 genes. 



(a) That characters often arise as rudiments and only 

 in the course of generations realize their full potentiality 

 is a well-known experience of breeders. Thus De Vries 2 

 states that the double Anemone coronaria was produced 

 by the owner of a nursery who, observing in his beds a 

 flower with a single broadened stamen, saved its seeds 

 separately and in the succeeding generations procured 

 beautifully filled flowers. By appropriate matings 

 Castle succeeded in 5 generations in getting much better 

 expressed polydactylism in guinea pigs than he had at 

 the outset. Dr. F. E. Lutz (1911) found a slight ab- 

 normality of venation in the fruit fly, Drosophila am- 

 pelophila. By in-breeding abnormally veined flies and 

 selecting as breeders the extremely abnormal flies he 

 eventually secured in the later generations some highly 

 abnormal individuals. From a hen that showed only a 

 slight extension of the web between certain toes I suc- 

 ceeded in breeding a race of profoundly syndactyl de- 

 scendants. 



(b) That mutations (" saltations'') run in parallel 

 lines in related species is well brought out in a table 

 given by Osborn (1912, p. 191), which I reproduce here 

 with certain modifications. 



That each germ plasm can vary only within certain 

 limits and that related germ plasms show only a limited 

 number of variations and the same in the different 

 species indicate that variations of the specific rank are 

 not determined by anything outside the organism, but by 

 the very nature of the organism. Thus, the rabbit shows 

 in its coat color the agouti coloration, and so does the 

 guinea pig. From this in the guinea pig have arisen 

 yellow, chocolate, black, albino and other colors; and a 

 similar series has been obtained for rabbits. The guinea 

 pig has produced an angora coat and so has the rabbit, 



2 "Species and Varieties," p. 491. 



