THE MULTICELLULAR ORGANISM. 1 49 



by means of the seed, of the physical and mental characteristics of the 

 father, affect all the questions which the human mind has ever raised in 

 regard to existence." — Rudolph Virchow (1848). 



The discovery that every human being at the beginning 

 of his existence is a simple cell, that this egg-cell is essen- 

 tially similar to those of other Mammals, and that the 

 forms arising during the evolution of this cell in Man and 

 in the other higher Mammals, are at first similar, — supplies 

 a basis from which we may trace the further processes of 

 evolution. In the first place we have convinced ourselves 

 of a fact which is of great importance to the empiric side 

 of the history of development, relating to those ontogenetic 

 facts which can be directly traced by means of the micro- 

 scope ; and this fact is that in Man as well as in other 

 animals the developed many-celled organism with all its 

 various organs proceeds from a simple cell. Secondly, as 

 regards the phylogenetic side of the question, the specu- 

 lative part of the History of Human Development, which 

 is based on those facts,^ ^^'e have reached the conclusion 

 that the original ancestral form of Man as of the other 

 animals was a one-celled organism. The whole difficult 

 problem of the History of Evolution is thus now reduced 

 to the simple question : " How has the complex many-celled 

 organism arisen from the simple one-celled form ? By what 

 natural process has the simple cell been transformed into 

 that complex life-apparatus with all its various organs, the 

 apparently rational and purposive construction of which we 

 admire in the developed body ? " 



Turning now to answer this question, we must bear in 

 mind the view to which we have already alluded, that the 

 many-celled organism is orL.ered and constituted on the 



