12 HISTORICAL SKETCH. 



nearly depopulated at successive periods, and then restocked ; and he gives, 

 as an alternative, that new forms may be generated " without the presence 

 of any mould or germ of former aggregates." I am not sure that I under- 

 stand some passages ; but it seems tliat he attributes much influence to the 

 direct action of the conditions of life. He clearly saw, however, the full 

 force of tlie principle of natural selection. 



The" celebrated geologist and naturalist. Yon Buch, in his excellent "De- 

 scription Physique dcs lies Canaries" (1836, p. 147), clearly expresses his 

 belief that varieties slowly become changed into permanent species, which 

 arc no longer capable of intercrossing. 



Rafinesquc, in his "New Flora of North America," published in 1836, 

 wrote (p. C) as follows : " All species might have been varieties once, and 

 many varieties are gradually becoming species by assuming constant and pe- 

 culiar characters:" but further on (p. 18) he adds, "except the original 

 types or ancestors of the genus." 



In 1813-41 Prof. Ilaldcman {Boston Journal of Nat. ///.s/., U. States, vol. 

 iv., p. 463) has ably given the arguments for and against the hypothesis of 

 the development and modification of species ; he seems to lean toward the 

 side of change. 



The " Ycstigcs of Creation" appeared in 1844. In the tenth and much 

 improved edition (1853) the anonymous author says (p. 155): "The propo- 

 sition determined on after much consideration is, that the several series of 

 animated beings, from the simplest and oldest up to the highest and most 

 recent, are, under the 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 organization terminating in the high- 

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

 erally marked by intervals of organic character, which we find to be a prac- 

 tical difficulty in ascertaining affinities; 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 believes thr.t organization pro- 

 gresses by sudden leaps, but that the eflccts produced by the conditions of 

 life arc gradual. lie argues with much force on general grounds that species 

 arc not immutable productions. But I cannot see how the two supposed 

 "impulses" account in a scientific sense for the numerous and beautiful co- 

 adaptations which wc sec throughout Nature ; I cannot see that we thus gain 

 any insight how, for instance, a woodpecker has become adapted to its pecu- 

 liar habits of life. " The work, from its powerful and brilliant style, though 

 di:<playing in the earlier editions little accurate knowledge and a gi-eat want 

 of scientific caution, immedi.itcly had a very wide circulation. In my opiu- 



