ORGANIC EVOLUTION — THE FACTORS tS 



The thegry of evolution, as I understand it, is founded 

 on the supposition — or rather I think I may say the 

 known fact — that the cells of a multicellular organism 

 such as man correspond during the successive stages of 

 the ontogeny, to the cells of the successive non-con- 

 jugating generations which intervene between one act 

 of conjugation and the next among unicellular organ- 

 isms. If this be admitted, it does not aflfect the argu- 

 ment that the mimber of cell-generations is in some cases 

 almost infinitely prolonged, — c. g. among aphides, — nor 

 even that new organisms in some instances arise from 

 non-conjugating cells as among bees, or by budding as 

 among the hydrozoa. The essential point is, that though 

 the cells remain adherent and undergo differentiation and 

 specialization, yet they are aU cell-descendants of the 

 genn cell, or the pair of conjugated germ cells, in pre- 

 cisely the same sense as the ceU-descendants of a uni- 

 cellular organism or conjugated pair of unicellular 

 organisms are its or their cell-descendants. By the 

 theory that inborn variations are alone ti'ansmissible, it 

 is assumed that no single cell of a multicellular organism 

 is in part or whole a product of any other co-existing 

 cell or cells, i. c. that it has not received from any of 

 them living constituents, but that it is merely a co- 

 descendant with the other cells from a common ancestry ; 

 for instance, that the germ cells are not in whole or 

 part products of the other co-existing cells, but are co- 

 descendants with the other cells from a common ancestry, 

 and do not receive from them living " gemmules," which 

 become part of them, and so alter their constitution as 

 to cause them to proliferate into organisms different 

 from that which would otherwise have arisen. If this 

 be true, if the germ cells are not even in part products of 

 the other co-existing cells, and if it be also admitted that 

 acquired variations cannot so alter the nutiitive fluids 

 as to produce similar vaiiations in the new organisms 



