THE BEGINNINGS OF LIFE. 557 



and also much more effectually, by some further Umita- 

 tions in respect to the meaning of the word ^species,' 

 such as the present state of our knowledge now renders 

 absolutely necessary. 



Must we suppose that all the forms of Life which 

 are capable of reproducing their like or of ^breeding 

 true' through successive generations, whether by a 

 sexual or by an asexual process, are to be considered 

 to belong to distinct ^ species ' ? Although this is the 

 view to which our previous remarks seemed to tend, 

 we must not hastily commit ourselves to any such 

 conception. 



We find living matter coming into existence de novo^ 

 and possessed of a marvellous plasticity, so that dif- 

 ferent parts of it may, in more or less rapid succession, 

 assume now one now another of a countless series of 

 organic forms. During each of these periods also we 

 find the several forms multiplying themselves by pro- 

 cesses of fission or gemmation, and all the products 

 of such multiplication capable of undergoing similar 

 sets of changes — the nature of which always vary ac- 

 cording to the precise, though unknown, molecular 

 qualities of the different kinds of living matter and 

 the conditions to which they are subjected. The pro- 

 ducts of a single stock may, moreover, display a con- 

 siderable amount of diversity, because the precise 

 molecular composition of the matter is so readily 

 altered, and because each of these alterations involves 



