This  process  of  transformation  of  the  ids  of  the  germ-plasm
will,  however,  reach  a  limit,  as  do  all  processes  of  selection,  when
its  continuance  is  no  longer  of  any  advantage.  All  adaptations
in  an  animal  remain  stationary  and  are  not  further  perfected,
directly  further  improvement  becomes  useless;  and  in  the
same  way  the  process  of  modification  and  elimination  of  the
ids,  which  forms  the  basis  of  other  adaptations,  will  cease  as  soon
as  the  completely  modified  ids  are  present  in  such  a  majority
that  the  others  can  only  exert  an  inappreciable  influence  on  the
nature  of  the  offspring.  The  usefiil  and  adaptable  characters
will  always  undergo  complete  development  in  the  normal  process
of  reproduction,  —  that  is  to  say,  in  the  intermingling  of
individuals  of  the  species,  —  even  though  some  unmodified  ids
may  be  present  in  the  germ-plasm.  Let  us  take  as  an  example
the  well-known  case  of  the  butterfly  Kallima  parallecta,  which
resembles  a  leaf.  The  resemblance  is  very  marked,  although
not  a  complete  one.  The  form  of  a  leaf,  with  its  midrib
and  veins,  —  some  regions  appearing  more  or  less  faded,  and
some  dry  or  wet,  and  even  of  the  appearance  of  a  dewdrop,  —  is
indicated  on  the  folded  wings,  but  only  certain  of  the  secondary
veins  on  the  right  and  left  of  the  middle  line  are  represented.
