HISTORICAL DEVELOPMENT OF ZOOLOGY 449 



Lamarck's four propositions are as follows : 



First Law. Life by its own activities tends continually to increase 

 the volume of every body that possesses it, and to increase the size of 

 all the parts up to a limit which it itself imposes. 



Second Law. The production of a new organ or part results from a 

 new need, which continues to be felt, and from the new movement which 

 this need originates and 

 sustains. 



Third Law. The de- 

 velopment of organs and 

 their power of action are 

 always in direct relation 

 to the employment of 

 these organs. 



Fourth Law. All that 

 has been acquired or 

 changed in the structure 

 of individuals during 

 their life is preserved by 

 generation and trans- 

 mitted to new individuals 

 which have undergone 

 these changes. 



Discussion of the 

 validity of these prin- 

 ciples still continues. 



Though Lamarck's 



. PT FIG. 233. Charles Darwin 



influence can be 



traced in his contemporaries and those who followed him, it 

 does not seem that he directly affected the far more important 

 work of Darwin. 



Without doubt biology owes a greater debt to Charles 

 Darwin (1809-1882, Fig. 233) than to any other man. He 

 compelled the attention of men in a way and to an extent 

 unsurpassed by any other writer. His labors were directed 

 not alone towards stating the doctrine of descent with 

 modification and marshaling evidence to its support, but 



