212 A STUDY IN HEREDITY 



cause the organism into which it subsequently proliferates to 

 reproduce congenitally the particular modification which the 

 parent acquired. Again, supposing some cause {e.g. some 

 disease) produced a modification (e.g. cavities in the lungs) in the 

 soma, and that, subsequently, in the absence of the cause, the 

 offspring developed the modification ; even this would not 

 constitute an absolute proof of the Lamarckian doctrine, though 

 it would raise a presumption in favour of it. For it must be 

 remembered that it is not asserted that a force acting on an 

 organism cannot produce such a change in the germ as will cause 

 the organism into which it develops to exhibit a variation similar 

 to the modification produced by the force in the parent ; but that 

 it is asserted that this coincidence, this mere coincidence, must, 

 from the nature of the case, be extremely rare, so very rare that, 

 as factors in evolution, such apparent, but only apparent, trans- 

 mission of acquired traits may practically be ignored. Only after 

 it had been shown that clear and indubitable cases of reproduction 

 by the offspring of the parents' modification are not uncommon 

 in nature could the truth of the Lamarckian doctrine be accepted 

 as proven. 



Watching the multiplication of an infusorian {Stylonychia 

 Fustulata), Maupas observed that, after two of these had 

 conjugated, the resulting fertilised cell divided and re-divided 

 many times without conjugation again occurring, but that if, after 

 a pretty certain definite number of cell-divisions, conjugation did 

 not again occur, the race ultimately died out. He found, more- 

 over, that the descendants of a conjugated pair did not conjugate 

 among themselves, but only with the descendants of another con- 

 jugated pair. All this is the rule among higher plants and animals. 

 The ovum and the sperm are unicellular organisms. After con- 

 jugation they divide and re-divide many times without conjugation 

 again occurring among the descendant cells. But these, like 

 infusorians, if they do not conjugate, ultimately die out. Most of 

 them {i.e. the somatic cells) are incapable of conjugation, while 

 such of them as are capable of conjugation {i.e. the germ cells) 

 conjugate only with cells from another body {i.e. cell-family). There 



