42 THE HOLLOW CURVE [ch. iv 



one side are to be regarded as successes, those upon the other as 

 failures. Nor can one picture to oneself a system in which the 

 number of failures that die out (and in all families more or less 

 alike) is at first to be about 38 per cent (the monotypic genera, of 

 one species), then only about 12 per cent (the genera of two 

 species) and so on in decreasing numbers. 



