2i8 ENVIRONMENT 



vegetables. Under artificial changes of environ- 

 ment the alteration of the proportion of salt in 

 the water in which it lives a shrimp (Artemia) 

 will become transformed by changes which would 

 suffice to distinguish not merely a new species, 

 but a new genus. Sponges and zoophytes which 

 have apparently migrated from the sea to a fresh- 

 water habitat, have changed the course of their 

 development : the organism emerges from the 

 egg in its adult form instead of as a free-swimming 

 larva. Breeds of English sheep transported to 

 the pampas of Argentina become endow r ed with 

 novel characters : the legs grow long at the 

 expense of the body : the wool turns coarse 

 and hairy. So substantial a distinction as that 

 between short-skulled and long-skulled races is 

 believed by some authorities to have resulted 

 merely from the differing influences of a moun- 

 tainous and a plains habitat ; and at the present 

 day an American environment appears to be 

 curiously modifying the Anglo-Saxon type in the 

 shape of the head, and in the modelling of the 

 features. If, as appears, changes of environment 

 are followed by hereditary modifications of form, 

 or stimulate the occurrence of hereditary muta- 

 tions, we may infer that migration has been a 

 powerful factor in the development of new species 

 of animals and races of mankind. 



,f| 



There appears to be, then, good warranty for 

 the conclusion that the action of environment 

 may produce changes which become fixed in the 

 breed and are passed on from parents to offspring. 

 The character of these changes may often appear 

 to have no connection with any special features 

 of the environment : it is not clear, for instance, 

 why birds should develop their powers of song 



