PEDIGEEE OF MONEEA. 4 1 



origin of the whole tribe during the course of enormous 

 periods of time. 



Upon the gi'ound of emhryological records, therefore, we 

 can with full assurance maintain that all many-celled, as 

 well as single-celled, organisms are originally descended from 

 simple cells ; connected with this, of course, is the conclusion 

 that the most ancient root of the animal and vegetable 

 kingdom was common to both. For the different primaeval 

 " original cells " out of which the few different main groups 

 or tribes have developed, only acquired their differences 

 after a time, and were descended from a common " primaeval 

 cell." But where did those few " original cells," or the one 

 primaeval cell, come from ? For the answer to this funda- 

 mental genealogical question we must return to the theory 

 of plastids and the hypothesis of spontaneous generation 

 which we have already discussed (vol. i. p. 327). 



As was then shown, we cannot imagine cells to have arisen 

 by spontaneous generation, but only Monera, those, primaeval 

 creatures of the simplest kind conceivable, like the still 

 living Protamoebae, Protomyxae, etc. (vol. i. p. 186, Fig. 1). 

 only such corpuscules of mucus without component parts — 

 whose whole albuminous body is as homogeneous in itself as 

 an inorganic crystal, but which nevertheless fulfils the two 

 organic fundamental functions of nutrition and propagation 

 — could have directly arisen out of inorganic matter by auto- 

 geny at the beginning (we may suppose) of the Laurentian 

 period. While some Monera remained at the original simple 

 stage of formation, others gradually developed into cells by 

 the inner kernel of the albuminous mass becoming separated 

 from the external cell-substance. In others, by differentiation 

 of the outermost layer of the cell-substance, an external 



