MONERA ALONE PRODUCED BY" SPONTANEOUS GENERATION. 33 



firstly, in point of logic, and secondly, in its scientific tenor 

 (p. xxvi). At the same time lie rightly shows that the 

 hypothesis of spontaneous generation, in the sense which 

 we have defined, is the " condition necessary to the conceiv- 

 ability of nature in accordance with the laws of causality." 



In conclusion, I repeat, with emphasis, that it is only in 

 the case of Monera of structureless organisms without 

 organs that we can assume the hypothesis of spontaneous 

 generation. Every differentiated organism, every organism 

 composed of organs, can only have originated from an 

 undifferentiated lower organism by differentiation of its 

 parts, and consequently by Phylogeny. Hence, even in the 

 production of the simplest cell we must not assume the pro- 

 cess of spontaneous generation. For even the simplest cell 

 consists of at least two distinct constituent parts ; the 

 inner and firmer kernel (nucleus), and the outer and 

 softer cell-substance or protoplasm. These two distinct 

 parts can only have come into being by differentiation of 

 the homogeneous plasson of a moneron and of a cytod. It 

 is for this very reason that the natural history of Monera is 

 of the highest interest ; for it alone can remove the principal 

 difficulties which beset the question of spontaneous genera- 

 tion. The extant Monera do afford us organless and struc- 

 tureless organisms, such as must have originated by spon- 

 taneous generation at the first beginning of organic life 

 upon the earth. 133 



