EVOLUTION 87 



"In animals and plants, whenever the conditions of 

 habitat, exposure, climate, nutrition, mode of life, et cetera, 

 are modified, the characters of size, shape, relations be- 

 tween parts, coloration, consistency, and, in animals, 

 agility and industry, are modified proportionately." 



As illustrating the direct effect of environment on organ- 

 isms, Lamarck chose a plant, the water-buttercup {Ran- 

 unculus aquatilis), which may grow in marshy places, or im- 

 mersed in water (Fig. 46). When immersed, the leaves 

 are all finely divided, but when not immersed, they are 

 merely lobed. 



While plants are more passive, and are affected by their 

 surroundings directly, through changes in nutrition, light, 

 gravity, and so on, animals react to environmental changes 

 in a more positive and less passive manner. Thus, in 

 the words of Lamarck:^ 



Important changes in conditions bring about impor- 

 tant changes in the animals' needs, and changes in their 

 needs bring about changes in their actions. If the new 

 needs become constant or durable, the animals acquire 

 new habits. . . . Whenever new conditions, becoming 

 constant, impart new habits to a race of animals 

 these habitual actions lead to the use of a certain part in 

 preference to another, or to the total disuse of a part which 

 is now useless . The lack of use of an organ, made 



constant by acquired habits, weakens it gradually until 

 it degenerates or even disappears entirely." Thus, "it 

 is part of the plan of organization of reptiles, as well as of 

 other vertebrates, that they have four legs attached to 

 their skeleton . . . but snakes acquired the habit of glid- 



' Translated from his Philosophie Zoologique, vol. I, pp. 227, 223, 224, 

 248. 



