xx THE INFLUENCE OF ENVIRONMENT 391 



milhausenii, which has not caudal lobes. He also found 

 that if the forms without caudal lobes were kept in brine 

 which was gradually diluted, these were replaced by 

 those of the A. salina type. The two forms are connected 



T 



by intermediate stages, and it seems that Artemia salina 

 is a species very variable as regards the tail and caudal 

 bristles. It seems, then, that what the environment 

 did in this case was to induce variability and to shunt the 

 variation in one direction or the other. 



FIG. 121. TAIL-LOBES OF Artemia salina (TO THE LEFT) AND OF Artemia 

 milhausenii (TO THE RIGHT) ; BETWEEN THESE FOUR INTERMEDIATE 

 STAGES. 



(From Chambers's Encyclop. ; after Schmankewitsch.) 



Many interesting experiments have been made on the 

 effect of chemical reagents on cells, a promising path of 

 discovery which has not yet been adequately appre- 

 ciated by medical investigators. By slight changes the 

 form of a cell and its predominant phase of activity may 

 be entirely changed. This is surely an important con- 

 sideration, when we remember that it was in single cells 

 that life began, and that all multicellular organisms 

 reproduced in the ordinary way begin their individual 

 life as single cells. Even Weismann agreed with Spencer's 

 conclusion that " the direct action of the medium was 

 the primordial factor of organic evolution." 



To Claude Bernard, the main problem of evolution 

 seemed to be concerned with variations in nutrition : 

 " L'evolution, c'est 1'ensemble constant de ces alternatives 

 de la nutrition ; c'est la nutrition considered dans sa 

 realite, embrassee d'un coup d'ceil a travers le temps." 

 John Hunter and others have shown how the walls of the 



