36 EVOLUTION, SOCIAL AND ORGANIC 



(2.) These new needs will compel these 

 animals to adopt new habits and discard some 

 old ones, and these needs and habits will pro- 

 duce and develop new organs. 



, (3.) The development or disappearance of 

 organs depends on their use or disuse. 



(4.) The effects of use or disuse, acquired 

 by animals, are transmitted by heredity to 

 their offspring. 



This fourth factor has split the biological 

 world since Weismann repudiated it in 1883. 



As a typical case of the operation of his 

 theory, Lamarck gives the following: "The 

 serpents having taken up the habit of gliding 

 along the ground, and of concealing them- 

 selves in the grass, their body, owing to con- 

 tinually repeated efforts to elongate itself so 

 as to pass through narrow spaces, has acquired 

 a considerable length disproportionate to its 

 size. Moreover limbs would have been very 

 useless to these animals, and consequently 

 would not have been employed because long 

 legs would have interfered with their need of 

 gliding, and very short legs, not being more 

 than four in number, would have been in- 

 capable of moving their body. Hence the lack 

 of use of these parts having been constant in 

 the races of these animals, has caused the 

 total disappearance of these same parts, al- 



