336 DARWINISM AND THE PROBLEMS OF LIFE 



at each part of the germ, one part of the innumer- 

 able determinants would become steadily larger and 

 the other part constantly smaller. In the same way 

 the organs of the developed animal would change in 

 all directions simultaneously. It would be impossible, 

 in view of this eternal ebb and flow of the determinants, 

 for an animal species to remain the same for a 

 considerable period, as we actually find. 



Hence Weismann is compelled to attribute to the 

 germ-substance a faculty of self-correction; that is to 

 say, generally speaking, a determinant will, if it receives 

 a somewhat richer supply of food, check it by its own 

 force, so that it will be neglected, and the determinant 

 in question will become weaker again. By this self- 

 regulation the determinants save themselves from 

 changing incessantly with every variation in the food- 

 supply. The force of self-correction is only overcome 

 in rare and exceptional cases of the access of a heavy 

 stream of nourishment. Then they grow constantly 

 larger, and with them the organs they bring into 

 existence. 



If the enlargement of the particular organ is useful 

 for the organism, its possessor is preserved by natural 

 selection, and therefore also the growing determinant. As 

 the individuals that vary in this way are selected they 

 come in time to dominate the species. But if the 

 enlargement of the organ is injurious, the animal in 

 question is destroyed and the upward movement of the 

 determinant is cut off. 



Up to the present we have only considered the 

 quantitative changes of the determinants and their organs. 



