The Hypothesis of Iiidiscriininate Mutability. 203 



pare the number of species in these geological series with 

 the wealth of our modern collective species in elementary 

 types. Can there be any question that this richness ex- 

 isted at all times in spite of the fact that there is no geo- 

 logical record of it?. 



We will again refer to the composite species Draba 

 verna, which has been so fully elucidated by Jordan. 

 Thuret, De Bary, Rosen and others. It is generally 

 assumed that all the elementary species of Draha vcrna 

 spring from a single original form ; yet they differ from 

 one another in every conceivable direction. They must 

 liave arisen as mutations from this form ; which must 

 therefore have produced them in all directions and not 

 in one particular one. They afford sufficient material 

 for natural selection ; whatever view of it we hold. 



Supposing that the ancestors of the horse exhibited 

 a similar indiscriminate mutability, what chance would 

 there be of their preservation in the fossil state? This 

 question is a difficult one to answer and calls for further 

 treatment. The present number of elementary types be- 

 longing to a species is no measure of the number of 

 mutations it may have produced since its origin. By 

 far the greater number of mutations presumably perish, 

 nipped in the bud by natural selection. Other forms 

 may continue for one or two years, but after a time, they 

 too disappear. It is only a very few which ultimately 

 come to take part in the great struggle for existence. 



Much that appears, must forthwith disappear. Even 

 between the male and female individuals of one and the 

 same species there is often a strong competition whicli 

 may result in a permanent alteration of their numerical 

 proportions. As a rule male plants are more delicate, 

 and we find quite regularly that in unfavoral)le positions 



