Galton's  essay  was  published  only  a  few  years  after  the  ap-
pearance of  Darwin's  theory  of  pangenesis ;  but  it  cannot  be
said  that  it  exercised  any  influence  on  the  subsequent  develop-
ment of  the  theory  of  heredity.  Apparently  it  was  not  much
noticed  even  in  England,  and  on  the  Continent  it  remained
unknown  for  a  long  time.  This  must  be  my  excuse  for  being
ignorant  of  the  existence  of  this  paper,  and  consequently  for


iNtkODtJCTtO>f  9

not  referring  to  it  in  my  essays  which  appeared  nearly  ten  years
later.*  In  one  of  these  essays  *  On  Heredity'  (1883),  I  con-
tested at  first  in  general  terms  not  only  the  existence  but  also
the  theoretical  possibility  of  the  transmission  of  acquired  charac-
ters, and  tried  to  release  the  theory  from  the  necessity  of  an
explanation  which  deprived  it  of  any  further  development.  In
this  essay  I  further  assumed  the  existence  in  the  germ-cell  of  a
reproductive  substance,  the  germ-plasm^  which  cannot  be  formed
spontaneously,  but  is  always  passed  on  from  the  germ-cell  in
which  an  organism  originates  in  direct  continuity  to  the  germ-
cells  of  the  succeeding  generations.  The  difference  between  the
^  body '  in  the  narrower  sense  (soma)  and  the  reproductive  cells
was  also  emphasised,  and  it  was  maintained  that  the  germ-cells
alone  transmit  the  reproductive  substance  or  germ-plasm  in  unin-
terrupted succession  from  one  generation  to  the  next,  while  the
body  (soma)  which  bears  and  nourishes  the  germ-cells,  is,  in  a
certain  sense,  only  an  outgrowth  from  one  of  them.
