IV THE CELL AND THE ORGANISM 75 



on the particular descent of plant forms. Thus the gameto- 

 phyte of the fern is a flat thallus-like plant which both in 

 form and character reminds one of an alga. And it is quite 

 possible that this form of the fern may give the clue of its 

 origin from some alga-like progenitor in the far-distant past. 

 May we not say that the prothallus of the fern appears to 

 connect the alga and the fern, and thus to bridge widely 

 separated epochs of the past in the evolution of plant forms? 

 I suggest the idea merely for further investigation. 



From speculations as to the origin of the cell we pass on 

 to consider the differentiations which have taken place 

 among cells generally, and the particular differentiation of 

 cells which has led to the divergence between plant and 

 animal forms. It is commonly thought that the animal 

 forms are a later development and advance on the earlier 

 plant forms. This idea is largely due to the fact that in the 

 animal there has been the special development of the new 

 factor of mind which, rapidly rising through the higher ani- 

 mals, has reached its highest level in the human individual. 

 But although animal forms may have developed farther 

 and come to attain to much higher levels than the plant 

 forms, the question of origins stands on a different foot- 

 ing. And the evidence points rather to a common 

 origin and to the earliest cells of life having been common 

 to both plants and animals. Thus the lowest forms of cell 

 life are even now practically indistinguishable into plant 

 and animal. And it is probable that this common phase, 

 prior to differentiation into plant and animal forms, must 

 have lasted a very long time and have been marked by 

 considerable advances in the development of the common 

 cells, especially in view of the probable fact, already noted, 

 that sexual reproduction of a fairly advanced type had 

 probably been reached before the bifurcation took place 

 and plants and animals were launched on their separate 

 careers. What advance in cell development had been 

 reached before this bifurcation it is impossible to say, as 

 only the very lowest unicellular organisms of a common 

 character still survive, and the geological record has no 



