134 Darwin, and after Darwin. 



inducing divergence— at any rate, so rapidly as we 

 might expect. There appears, however, to be 

 another factor, the presence or absence of which 

 makes a great difference. This, as stated in the text, 

 is the degree in which a specific type is stable or 

 unstable — liable or not liable to vary. Thus, for 

 example, the Goose is what Darwin calls an " inflex- 

 ible " type as compared with most other domesticated 

 birds. Therefore, if a lot of geese were to be indis- 

 criminately isolated from the rest of their species, the 

 probability is that in a given time their descendants 

 would not have diverged from the parent type to such 

 an extent as would a similar lot of ducks under 

 similar circumstances: the more stable specific type 

 would require a longer time to change under the 

 influence of apogamy alone. Now, the butterflies 

 and crustaceans quoted by Weismann may be of a 

 highly stable type, presenting but a small range 

 of individual variability ; and, if so, they would 

 naturally require a long time to exhibit any change 

 of type under the influence of apogamy alone. But, 

 be this as it may, Weismann himself adduces these 

 cases merely for the sake of showing that there are 

 cases which seem to tell against the general prin- 

 ciple of modification as due to apogamy alone — i.e. 

 the general principle which, under the name amixia, 

 he is engaged in defending. And the conclusion 

 at which he himself arrives is, that while it would 

 be wrong to affirm that apogamy must in all 

 cases produce divergence, we are amply justified 

 in affirming that in many cases it may have done 

 so ; while there is good evidence to prove that in 

 not a few cases it has done so, and therefore 



