196 EXPERIMENTAL EVOLUTION LECT. 



considerable differences are noticeable in the evolution 

 of individuals. The less carbonate there remains, 

 the slower is the development ; and in no case does 

 the larva go any further than the Pluteus stage. But 

 the most interesting fact is that these embryos do not 

 acquire the spicules which are so characteristic of 

 their structure. The problem now consists in 

 obtaining such abnormal embryos with sufficient 

 vitality to keep alive, for the Pluteus obtained by 

 Pouchet and Chabry have always proved unable to 

 outlive the stage known by the same name. Recently 

 also M. Marcacci has shown that when eggs of the 

 common fowl are subjected to motion during^ the 

 period of incubation, abnormal chicks are obtained 

 and this is a new method of producing monsters. 



The foregoing general facts are enough to entitle us 

 to draw the conclusion that environmental changes, 

 while in many cases liable to cause rapid death, or 

 considerable disturbance of vital functions, may in 

 others, and especially when care is taken not to 

 produce too important modifications, result in 

 organisms which diverge widely from the common 

 form. As yet, however, the divergences have been 

 too great, involving changes which make life impos- 

 sible. But new investigations may show that this 

 influence of environment can be reduced in degree, 

 so that the organisms thus modified may be able 



