ORGANIC EVOLUTION —PHYSICAL 43 



is derived, i. e. not a germ cell from the same body, but 

 only with a germ from another body. 



Thus these remote cell-descendants of the original 

 pair of cells which conjugated, and from which the body 

 to which they belong is derived, exhibit, after many 

 generations, the same peculiarity which Maupas found 

 distinguished the remote cell-descendants of conjugated 

 unicellular organisms ; viz. that after a certain number 

 of cell-generations, unless conjugation occurs anew, 

 they perish, and with them the race. The other cells 

 which do not conjugate cease in time, like Maupas' 

 infusorians, to multiply, and, like those infusorians, 

 perish, and with them the individual of whom they 

 generally form the chief part. 



The above seems to bear out the theory that con- 

 jugation causes a " rejuvenescence and revitalization " 

 without which the race cannot persist ; but on closer 

 examination the facts are found to point the other way. 

 The number of cell-generations following conjugation 

 differs in different individuals of the same species, and 

 may be made to differ in each individual by variations 

 in nutrition, exercise, &c. It differs enormously in 

 different species of plants and animals ; thus the 

 number of cell-generations following conjugation is 

 enormously fewer in minute plants and insects than in 

 such great plants and animals as pines and whales. 

 Moreover the number of non-conjugating cell-genera- 

 tions is almost infinitely prolonged along certain lines in 

 such animals as the aphides, which reproduce asexually 

 during the whole summer, and reproduce sexually only 

 on the advent of cold weather, and which, were the 

 warm weather to continue, might reproduce asexually 

 for ever. It is infinitely prolonged in such plants as 

 multiply by means of suckers, or are propagated by 

 cuttings, without their cells ever conjugating. The 

 theory therefore that conjugation causes a " rejuvenes- 



