NATURAL HISTORY OF THE EIGHTEENTH CENT. 395 



they inhabit by general absorption. These points of animated jelly 

 appear to be perfectly homogeneous through their whole mass, and 

 having little consistence, they cannot be said to possess organs at all. 



Lamarck's explanation of these facts is that all the species of animals 

 have been formed by nature, beginning with more simple or imperfect, 

 and proceeding gradually to the more complex forms. The modi- 

 fication of organs in different animals he attributes to changes in the 

 habits of the animals occasioned by changes in the surrounding cir- 

 cumstances. That changes in the circumstances in which a plant or 

 animal is placed will give rise to changes in its form, colours, etc., he 

 adduces many well-known cases to prove, as, for instance, the diffe- 

 rences which cultivation produces in plants. Changes of the surround- 

 ing circumstances will cause changes in the wants of animals ; changes 

 in the wants will determine changes in the habitual actions ; and habi- 

 tual actions will influence the organs according to the well-known law 

 that constant disuse of an organ weakens and diminishes that organ, 

 so that at length it may become powerless ; while, on the other hand, 

 habitual use will increase the power of an organ. Lamarck's idea was 

 that these effects on the individual are transmitted to the offspring, 

 and if the same conditions are continued through a long succession of 

 generations, the divergences from the original stock widen until the 

 differences of organization are such as we recognize in the various 

 species. 



The explanation of the origin of the difference in species by changes 

 induced in individual animals by 

 their habits of life, was the weakest 

 part of the Lamarckian theory: 

 To explain, for example, the pe- 

 culiarities of the wading birds, he 

 supposes that originally some birds, 

 compelled to resort to shallow 

 waters and the margins of streams 

 for their prey, being unwilling to 

 swim or even to wet their bodies 

 in the water, used every effort to 

 stretch out their feet, and that by 

 long-continued efforts of this kind 

 it came to pass that the birds were 

 at length provided with legs on 

 which they are mounted as if on 

 stilts. The inadequacy of La- 

 marck's theory on this subject is 

 perhaps more obvious in the fol- FlG ' lSl - FLAMINGOS '_ 



lowing illustration from the same chapter : " Among the carnivorous 

 animals are some which are obliged to catch their prey by their speed ; 

 now such an animal, whose wants, and therefore habits, require that it 



