50 THE EVOLUTION OF MAK. 



sea, raises many different inquiries and thoughts. Spon- 

 taneous generation, especially, is naturally suggested by the 

 Bathybius. We have already found that, for the origin of 

 first Monera upon our globe, the assumption of spontaneous 

 generation is a necessary hypothesis. We shall be all the 

 more inclined to confirm it now that, in the Monera, we have 

 recognized those simplest organisms, the origin of which 

 by spontaneous generation, in the present condition of our 

 science, no longer involves very great difficulties. For the 

 Monera actually stand on the very boundary between 

 organic and inorganic natural bodies.^^ 



Next* to the simple cy tod-bodies of the Monera, as the 

 second ancestral stage in the human pedigree (as in that of 

 all other animals), comes the simple cell, that most undifieren- 

 tiated cell-form, which, at the present time, still leads an 

 independent solitary life, as the Amoeba. For the first and 

 oldest process of organic difierentiation, which aflfected the 

 homogeneous and structureless plasson-body of the Monera, 

 caused the separation of the latter into two difierent sub- 

 stances ; an inner firmer substance, the kernel, or nucleus, 

 and an outer, softer substance, the cell-substance, or 

 protoplaama. By this extremely important separative pro- 

 cess, by the difierentiation of the plasson into nucleus and 

 protoplasm, the organized cell originated from the structure- 

 less cytod, the nucleolated from the non-nucleolated plastid. 

 That the cells which first appeared upon the earth origin- 

 ated in tnis manner, by the difierentiation of the Monera, is 

 a conception which in the present condition of histological 

 knowledge seems quite allowable ; for we can even yet 

 directly observe this oldest histological process of difier- 

 entiation in Ontogeny. It will be remembered that in the 



