EVOLUTION OF THE COLORS OF BIRDS. 35 



of observed cases of the direct action of the environment 

 in affecting a race. One of the finest is the transforma- 

 tion of the brine-shrimp, Artemia, reported by Schman- 

 kewitsch: " One species of this crustacean, Artemia sa- 

 lina," says Lloyd Morgan, "lives in brackish water, 

 while A. milhausenii inhabits water which is much salter. 

 They have always been regarded as distinct species, dif- 

 fering in the form of the tail lobes and the character of 

 the spines they bear. And yet, by gradually altering 

 the saltness of the water, either of them was transformed 

 into the other in the course of a few generations. So 

 long as the altered conditions remained the same the 

 change of form was maintained." 



What is to be said of such cases? Do they constitute 

 a proof positive of the inheritance of acquired characters? 

 At first sight they certainly do appear to be conclusive 

 and final, but a candid examination of them compels us 

 to admit of the possibility of a different interpretation. 

 The two examples mentioned are fairly representative 

 of a large number of similar instances. The whole diffi- 

 culty with them lies in the fact that when the organism 

 is restored to its former conditions the change does not 

 persist. Does the son of a blacksmith inherit the strong 

 arms of his father? Probably he does, but this is not 

 equivalent to asserting that he inherits the strength 

 acquired by his father in following his vocation. It is 

 not improbable that his father became a blacksmith be- 

 cause he was naturally strong or was predisposed to 

 develop unusual strength. We must first in every case 

 assure ourselves that the predisposition does not exist in 

 the animal and only requires a favorable environment 

 to be developed. Secondly, it must be demonstrated 

 that there is a progressive change from one generation 

 to the next. This there apparently was in the case of 

 the goldfish, for a period of six years was required for 



