394 THE CAUSES OF THE xi 



shown by the Abb4 Trembley many years ago so 

 can he do the same thing with many of the lower 

 forms of animal life. M. de Trembley showed 

 that you could take a polype and cut it into two, 

 or four, or many pieces, mutilating it in all direc- 

 tions, and the pieces would still grow up and re- 

 produce completely the original form of the animal. 

 These are all cases of non-sexual multiplication, 

 and there are other instances, and still more extra- 

 ordinary ones, in which this process takes place 

 naturally, in a more hidden, a more recondite kind 

 of way. You are all of you familiar with that 

 little green insect, the Aphis or blight, as it is 

 called. These little animals, during a very con- 

 siderable part of their existence, multiply them- 

 selves by means of a kind of internal budding, the 

 buds being developed into essentially non-sexual 

 animals, which are neither male nor female ; they 

 become converted into young Aphides, which re- 

 peat the process, and their offspring after them, 

 and so on again ; you may go on for nine or ten, 

 or even twenty or more successions ; and there is no 

 very good reason to say how soon it might terminate, 

 or how long it might not go on if the proper con- 

 ditions of warmth and nourishment were kept up. 

 Sexual reproduction is quite a distinct matter. 

 Here, in all these cases, what is required is the 

 detachment of two portions of the parental 

 organisms, which portions we know as the egg 

 or the spermatozoon. In plants it is the ovule 



