HISTORICAL SKETCH. xix 



providence of God, the results, first, of an impulse which 

 has been imparted to the forms of life, advancing them, 

 in definite times, by generation, through grades of or- 

 ganisation terminating in the highest dicotyledons and 

 vertebrata, these grades being few in number, and gen- 

 erally marked by intervals of organic character, which 

 we find to be a practical difficulty in ascertaining affini- 

 ties; second, of another impulse connected with the 

 vital forces, tending, in the course of generations, to 

 modify organic structures in accordance with external 

 circumstances, as food, the nature of the habitat, and 

 the meteoric agencies, these being the ' adaptations ' of 

 the natural theologian." The author apparently be- 

 Ueves that organisation progresses by sudden leaps, but 

 that the effects produced by the conditions of life are 

 gradual. He argues with much force on general grounds 

 that species are not immutable productions. But I can- 

 not see how the two supposed " impulses " account in a 

 scientific sense for the numerous and beautiful co- 

 adaptations which we see throughout nature; I cannot 

 see that we thus gain any insight how, for instance, a 

 woodpecker has become adapted to its peculiar habits 

 of life. The work, from its powerful and brilliant style, 

 though displaying in the earlier editions little accurate 

 knowledge and a great want of scientific caution, imme- 

 diately had a very wide circulation. In my opinion it 

 has done excellent service in this country in calling at- 

 tention to the subject, in removing prejudice, and in 

 thus preparing the ground for the reception of analogous 

 views. 



In 1846 the veteran geologist M. J. d'Omalius d'Hal- 

 loy published in an excellent though short paper (' Bul- 

 letins de I'Acad. Roy. Bruxelles,' torn. xiii. p. 581) 



