LARVAE OF ARBACIA PUNCTULATA 



427 



conditions. A fluctuating variation might therefore be benefi- 

 cial to the individual and a mutation to the species also, even 

 though it might be termed an abnormality. 



What, then, may the range of variation in the Arbacia larvae 

 be? No attempt could be made to answer this for mutations; 

 but for such variations as are inherited and for such as are pro- 

 duced by modification of the medium, some idea may be drawn 



