4 . Descent 



comparative sciences compels us to accept the 

 idea. To deny it, is to give up all oppor- 

 tunity of conceiving Nature in her true form. 



The general features of the theory of descent 

 are now accepted as the basis of all biological 

 science. Half a century of discussion and in- 

 vestigation has cleared up the minor points and 

 brought out an abundance of facts; but these 

 have not changed the principle. Descent with 

 modification is now universally accepted as the 

 chief law of nature in the organic world. In 

 honor of him, who with unsurpassed genius, and 

 by unlimited labor has made it the basis of 

 modern thought, this law is called the " Dar- 

 winian theory of descent. ' ' 



Darwin 's second contribution to this attain- 

 ment was his proof of the possibility of a phys- 

 iological explanation of the process of descent 

 itself. Of this possibility he fully convinced his 

 contemporaries, but in indicating the particular 

 means by which the change of species has been 

 brought about, he has not succeeded in securing 

 universal acceptation. Quite on the contrary, 

 objections have been raised from the very out- 

 set, and with such force as to compel Darwin 

 himself to change his views in his later writings. 

 This however, was of no avail, and objections 

 and criticisms have since steadily accumulated. 



Physiologic facts concerning the origin of 



