SPONTANEOUS GENERATION AND EVOLUTION : CONCLUSION 367 



Up till now all attempts to discover these conditions have been 

 futile, and I do not believe that they Avill ever be successful, not 

 because the conditions must be so peculiar in nature that we cannot 

 reproduce them, but. above all, because we should not be able to 

 perceive the results of a successful experiment. I sliall be able to 

 prove this convincingly without difficult}^ 



If we ask ourselves the question how the livino- beings which 

 might have arisen through spontaneous generation must be consti- 

 tuted, and on the other hand, in regard to what kinds of living forms 

 we can maintain with certainty that they could not have arisen tlms, 

 it is obvious that we must place on the latter list all organisms which 

 presuppose the existence of others, from which they have been 

 derived. But to this category belong all the organisms which possess 

 a germ -plasm, an idioplasm that we conceive of as composed of priniary 

 constituents (Anlagen) whicli have gradually been evolved and 

 accumulated through a long series of ancestors. Thus not only all 

 multicellular animals and plants which reproduce by means of germ- 

 cells, buds, and so forth, but also all unicellular organisms, must be 

 placed in this class. For these last — as we have seen— possess in 

 their nucleus a substance made up of primary constituents, without 

 which the mutilated body is unable to make good its loss, in short, an 

 idioplasm. That this plays the same role in unicellular as in multi- 

 cellular organisms we can infer with the greatest certainty from the 

 process of amphimixis, which runs its course in an analogous way in 

 both cases. 



Thus, even though we did not know what Ehrenberg demon- 

 strated in the third decade of last centurj^ that Infusorians in an 

 encapsuled state can be blown about everywhere, and can even be 

 carried across the ocean in the dust of the trade-Avinds, to re-awaken 

 to life wherever they fall into fresh water, we should still not have 

 remained at the standpoint of Leuwenhoek, Avho regarded Infusorians 

 as having arisen through spontaneous generation. They cannot arise 

 in this way, nor can they have done so at any time, because they 

 contain a substance made up of primary constituents, which can only 

 be of historic origin, and cannot therefore have arisen suddenly after 

 the manner of a chemical combination. 



The same is true of all the unicellular organisms, even of those 

 which are much more simple in structure than the Infusorians, whose 

 differentiation into cortical and medullary substances, oral and anal 

 openings, complex arrangements of cilia and much else, betokens 

 a hip-h deo-ree of differentiation in the cell. But even the Amcieba is 

 onl}^ apparently simple, for otherwise it could not send out processes 



