138 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



has so often been maintained ? In living nature, 

 observation enables us to answer that this is in no 

 way the case. Existing species, setting aside certain 

 rare cases of hybridization, are not connected with 

 one another by imperceptible transitions. This is an 

 important fact which did not fail to impress Darwin, 

 and one which that eminent observer endeavoured 

 to explain by hypotheses on the extinction of in- 

 termediate forms. However ingenious these hy- 

 potheses may be, they should not cause us to forget 

 the great observed fact, which is general among 

 existing animals. 



