STUDIES IN ANIMAL LIFE. 119 



Tree of Life, which, fills with its dead and broken 

 branches the crust of the earth, and covers the sur- 

 face with its ever-branching and beautiful ramifica- 

 tions."* 



It will not be expected that in these brief and 

 desultory remarks I should touch on all, or nearly 

 all, the important points in the discussion respect- 

 ing the fixity of species. Mr. Darwin's book is in 

 every body's hands, and my object has been to fa- 

 cilitate, if possible, the comprehension of his book, 

 and the adoption of a more philosophical hypothe- 

 sis, by pointing out the weakness of the chief argu- 

 ment on the other side. There is one more argu- 

 ment which may be noticed the more so as it is 

 constantly adduced with triumph by the one school, 

 and admitted as a difficulty by the other. Its force 

 is so great that it prevents many from accepting 

 the development hypothesis. It is the argument 

 founded on the alleged impossibility of hybrids 

 continuing the race. More than two or three gen- 

 erations of hybrids, it is said, can never be main- 

 tained; after that, the new form perishes, thus 

 clearly showing how Nature repudiates such amal- 

 gamations, and keeps her species jealously distinct 

 and invariable. This argument is held to be the 

 touchstone of the doctrine of species. I wish it 

 were so ; because, in that case, the question would 

 no longer be one of hypothesis, since we have now 

 the indubitable proof that some hybrids are fertile 

 unto the thirteenth generation and onward. 



* DARWIN : Origin of Species, p. 128. 



