328 LAMARCK, HIS LIFE AND WOUIC 



Nature has gradually created the different organs of 

 animals, varying the structure and situation of these 

 organs according to circumstances, and has progres- 

 sively improved their powers. She has begun by 

 borrowing from without, so to speak — from the en- 

 vironment — the productive force, both of organic 

 movements and those of the external parts. " She 

 has thus transported this force [the result of heat, 

 electricity, and perhaps others (p. 307)] into the ani- 

 mal itself, and, finally, in the most perfect animals 

 she has placed a great part of this force at their dis- 

 posal, as I will soon show." 



This force incessantly introduced into the lowest 

 animals sets in motion the visible fluids of the body 

 and excites the irritability of their contained parts, 

 giving rise to different contractile movements which 

 we observe ; hence the appearance of an irresistible 

 propensity {penchant) which constrains them to ex- 

 ecute those movements which by their continuity or 

 their repetition give rise to habits. 



The most imperfect animals, such as the Infusoria, 

 especially the monads, are nourished by absorption 

 and by " an internal inhibition of absorbed matters." 

 " They have," he says, " no power of seeking their 

 food, they have not even the power of recognizing 

 it, but they absorb it because it comes in contact 

 with every side of them {avec tous les points de leur 

 individu), and because the water in which they live 

 furnishes it to them in sufficient abundance." 



" These frail animals, in which the subtile fluids of 

 the environing milieux constitute the stimulating 

 cause of the orgasm, of irritability and of organic 



