392 THE CAUSES OF THE 



XI 



I now, then, take up the next question, What 

 do we know of the reproduction, the perpetuation, 

 and the modifications of the forms of living beings, 

 supposing that we have put the question as to their 

 origination on one side, and have assumed that at 

 present the causes of their origination are beyond 

 us, and that we know nothing about them ? Upon 

 this question the state of our knowledge is ex- 

 tremely different ; it is exceedingly large : and, if 

 not complete, our experience is certainly most ex- 

 tensive. It would be impossible to lay it all before 

 you, and the most I can do, or need do to-night, is 

 to take up the principal points and put them be- 

 fore you with such prominence as may subserve 

 the purposes of our present argument. 



The method of the perpetuation of organic beings 

 is of two kinds, the non-sexual and the sexual. In 

 the first the perpetuation takes place from and by 

 a particular act of an individual organism, which 

 sometimes may not be classed as belonging to any 

 sex at all. In the second case, it is in con- 

 sequence of the mutual action and interaction of 

 certain portions of the organisms of usually two 

 distinct individuals, the male and the female. The 

 cases of non-sexual perpetuation are by no means 

 so common as the cases of sexual perpetuation ; 

 and they are by no means so common in the animal 

 as in the vegetable world. You are all probably 

 familiar with the fact, as a matter of experience, 

 that you can propagate plants by means of what 



