191.  Not  only  is  the  limb  independently  variable,   but   each
smallest  part  of  it  possesses  the  same  power.     Suppose  a   child
comes  into  existence  with  a  malformed  limb.     This  variation  may
be  compounded  of  any  number  of  smaller  variations,  some  of  which

1  "  I  may  here  add  a  remark  made  by  Mr  Wicking,  who  has  had  more  experi-
ence than  any  other  person  in  England  in  breeding  pigeons  of  various  colours,
namely,  that  when  a  blue,  or  a  chequered  bird,  having  black  wing  bars,  once
appears  in  any  race  and  is  allowed  to  breed,  these  characters  are  so  strongly
transmitted  that  it  is  extremely  difficult  to  eradicate  them  "  (Animals  and  Plants,
vol.  i.  p.  210).  On  the  other  hand  if,  for  example,  albino  mice  be  crossed  with
black-and-white  Japanese  waltzing  mice,  the  ancestral  grey  colour  appears,  but
if  the  mongrels  be  inter-bred,  the  albino  and  the  black-and-white  types  reappear.
In  this  case  the  albino  and  the  black-and-white  colour  become  merely  dormant
when  the  grey  reappears.  Medelians  will  dispute  the  inference,  but  it  can  be
substantiated  (see  chapter  vii.).
THE  MASKING  OF  RETROGRESSION  117

are  progressions  and  others  retrogressions.  If  we  think  of  each  of
the  component  variations  separately,  and,  if  necessary,  analyse
them,  we  see  that  every  progression  must  be  built  on  the  develop-
ment as  presented  by  the  parent,  must  consist  of  an  addition
after  a  complete  recapitulation  (as  far  as  that  character  is  concerned)
of  the  life-history  as  presented  by  the  parent ;  whereas  every
retrogression  must  consist  of  a  subtraction  from  the  complete
recapitulation — a  reversion.  Think  how  we  will,  puzzle  how  we
may,  we  must  always  arrive  at  the  conclusion  that  retrogression  is
identical  with  reversion.
