ILLUSTRATIVE OF NATURAL SELECTION. 165 



tribution of Arctic Plants," (Trans. Linn. Soc. xxiii., 

 p. 310) Dr. Hooker says: "The 'most able and ex- 

 perienced descriptive botanists vary in their estimate 

 of the value of the f specific term ' to a much greater 

 extent than is generally supposed." . . "I think 

 I may safely affirm that the * specific term ' has three 

 different standard values, all current in descriptive 

 botany, but each more or less confined to one class 

 of observers." . . u This is no question of what 

 is right or wrong as to the real value of the spe- 

 cific term ; I believe each is right according to the 

 standard he assumes as the specific." 



Lastly, I will adduce Mr. Bates's researches on the 

 Amazons. During eleven years he accumulated vast 

 materials, and carefully studied the variation and dis- 

 tribution of insects. Yet he has shown that many 

 species of Lepidoptera, which before offered no special 

 difficulties, are in reality most intricately combined 

 in a tangled web of affinities, leading by such gradual 

 steps from the slightest and least stable variations to 

 fixed races and well-marked species, that it is very 

 often impossible to draw those sharp dividing-lines 

 which it is supposed that a careful study and full 

 materials will always enable us to do. 



These few examples show, I think, that in every 

 department of nature there occur instances of the in- 

 stability of specific form, which the increase of mate 

 rials aggravates rather than diminishes. And it must 

 be remembered that the naturalist is rarely likely to 

 err on the side of imputing greater indefiniteness to 



