ORIGIN OF THE DIVERSE FORMS OF ANIMAL LIFE 351 



their characteristics, scientists would be warranted in 

 recognizing the two forms as separate species. 



A species of moth of the genus Saturnia, brought from 

 Texas to Switzerland, where the young fed on the European 



PIG. 393. The Mastodon, an early ancestor of the elephant and long since extinct. 

 From a painting by Knight in the American Museum of Natural History. 



walnut, presented after one generation such marked differ- 

 ences from the same species whose young fed in Texas on 

 the black walnut, that entomologists gave it a new name. 

 The brine shrimp, Artemia salina, lives in slightly brackish 

 water, while Artemia milhauseni occurs only in very salt 

 water. If salt be gradually added to the vessel containing 

 the former species, it will in a few generations during the 

 months of a single summer, transform into the latter species. 

 Likewise, Artemia milhauseni will, in a few months, change 



