98 . STUDIES IN ANIMAL LIFE. 



of species. Yet no sooner do we understand that 

 species means a relation of resemblance between 

 animals, than the question of the fixity or varia- 

 bility of species resolves itself into this : Can there 

 be any variation in the resemblances of closely al- 

 lied animals? A question which would never be 

 asked. 



No one has thought of raising the question of 

 the fixity of varieties, yet it is as legitimate as that 

 of the fixity of species ; and we might also argue 

 for the fixity of genera, orders, classes, the fixity of 

 all these being implied in the very terms ; since no 

 sooner does any departure from the type present 

 itself, than by that it is excluded from the category ; 

 no sooner does a white object become gray or yel- 

 low, than it is excluded from the class of white ob- 

 jects. Here, therefore, is a sense in which the phrase 

 " fixity of species" is indisputable ; but in this sense 

 the phrase has never been disputed. When zoolo- 

 gists have maintained that species are variable, they 

 have meant that animal forms are variable; and 

 these variations, gradually accumulating, result at 

 last in such differences as are called specific. Al- 

 though some zoologists, and speculators who were 

 not zoologists; have believed that the possibility of 

 variation is so great that one species may actually 

 be transmuted into another, i. e., that an ass may be 

 developed into a horse, yet most thinkers are now 

 agreed that such violent changes are impossible, 

 and that every new form becomes established only 



