16 BIOLOGICAL SOCIETY OF WASHINGTON. 



' ' In the same climate very different situations and exposures 

 cause individuals thus placed at first simply to vary; but in the 

 course of time the continual differences of situation of the indi- 

 viduals of which I speak, living and reproducing under the 

 same conditions, bring about in them differences which become 

 in some sort essential to their existence, so that at the end of 

 many generations which succeed each other those individuals 

 which belonged originally to another species find themselves 

 transformed into a new species, distinct from the other." * 



The two great causes to which he ascribes this transforma- 

 tion are: i, what he calls the "circumstances," and 2, the 

 " habits " of the creatures transformed, and to enforce this 

 idea he lays down the following ' ' zoological principle ' ' the 

 fundamental truth of which, he says, appeared to him incon- 

 testable : 



' ' Progress in the structure {compositio?i) of the organization 

 undergoes here and there in the general series of animals 

 anomalies brought about by the character of the habitat 

 {cir con stances d' habitation), and by that of habits contracted, "f 



Between the "circumstances" and the "habits," however, 

 Lamarck perceived a casual relation, and this he expressed in 

 the following argumentative form : 



"The true order of things to be considered in all this con- 

 sists in recognizing : 



I St. That every permanent change of any consequence in 

 the circumstances under which each race of animals finds 

 itself effects within it a real change in their needs ; 



2d. That every change in the needs of animals necessitates 

 for them other actions to satisfy the new needs, and hence, 

 other habits ; 



♦ *Op. cit., Vol. I, pp. 79-80. 

 top. cit., Vol. I, p. 145. 



