P EERIER ON THE THEORY OF DESCENT. 525 



inorganic to the organic. Secondly, he refused to account, by it alone, 

 that is, by the combined action of the environment and of heredity, 

 for living forms ; but had recourse, to explain some among them, to 

 an internal nisus, or an original preformation analogous to final causes. 

 Lastly, he believed that the general laws of evolution expired in some 

 way at the threshold of the human world, and that human consciousness 

 is formed after other laws than the organic consensus. It was the part 

 of philosophy, now in possession of an idea of science which it owes 

 largely to the scientific men themselves, to indicate these later reserves. 

 For it is, after all, no small matter to know what is of science and what 

 is not. It is imperatively necessary for us to fix our eyes on this 

 capital point, and to decide among ourselves whether those who in 

 their researches accord a part to final causes, and attribute an excep- 

 tional position in nature to man, are performing a work of science or 

 of metaphysics. This is why, without losing sight of the rare merits 

 of the work we have named, we have thought it proper to point out 

 the ambiguous character of some parts of it. 



Now, M. Perrier has resolutely canceled most of his reserves. The 

 second part of his preface, in which he for the first time traces the 

 geographical distribution of the species of terrestrial lumbrici, and 

 points out the consequences of such distribution both in respect to 

 specific characteristics and from the geological point of view, is out of 

 our province to consider. The first part, which is devoted to a gen- 

 eral appreciation of Darwin's work, has a high philosophical signifi- 

 cance ; and we here give a summary of the whole of it. 



" Until within the last twenty years," says the author, " living 

 beings were nearly always studied independently of the medium in 

 which they live and of the relations which they form with each other. 

 Each of them appeared to be a distinct entity, owing nothing except 

 to itself, capable of abstracting itself from every modifying action on 

 the part of external agents, created once for all in view of certain con- 

 ditions of existence, marvelously adapted to these conditions, but 

 unable to extricate itself from them except at the cost of perishing, 

 in perfect equilibrium with the supposed unchangeable medium, but 

 destined to disappear whenever the equilibrium was broken. This 

 false conception of the living being has caused the failure of every 

 essay at a philosophy of the natural sciences which has been attempted 

 till now." 



M. Perrier then shows by a small number of selected examples that 

 each being, under the pressure of variable circumstances is, aside from 

 any preconceived plan, adapted to its environment, even when it may 

 not have seemed primarily destined to live in it ; some fishes to a life 

 in the air, some mammals and some birds to an aquatic life. He re- 

 marks that the living beings of the environment are the preponderant 

 part of the medium for each species. Adaptations not less close than 

 those which unite organisms to the physical medium, put organisms in 



