The  young  male  and  young  female  resemble  the  adult
female.  The  male,  when  it  becomes  mature,  undergoes  marked
changes  in  several  of  its  characters.  The  snout  becomes  more
elongated.  The  first  dorsal  fin  is  much  prolonged  vertically,
the  first  ray  longest,  the  posterior  successively  shorter.  The
second  dorsal  and  the  ventral  fins  increase  in  size,  the  posterior
rays  especially  elongating,  till,  when  depressed,  they  reach
beyond  the  base  of  the  caudal  fin.  There  is  a  distinct
genital  papilla,  visible  even  in  specimens  only  2  inches  in
length,  but  longest  in  mature  fish.  The  metamorphosis  takes
place  gradually,  and  its  completion  is  not  constantly  related
to  a  particular  size,  nor  to  the  attainment  of  sexual  maturity;
that  is  to  say,  as  in  many  other  cases,  male  specimens  are
often  sexually  mature  before  the  secondary  characters  have
attained  their  maximum  development.  A  striking  change  in
coloration  also  occurs.  While  the  back  retains  the  marbled
brown  markings,  the  front  and  sides  of  the  head,  the  sides  of
the  body,  and  the  pelvic,  dorsal,  and  caudal  fins  become
decorated  with  bands  of  bright  blue  and  yellow.  The  eye,
reddish-brown  or  cupreous  in  females  and  young  males,
becomes,  in  large  breeding  males,  of  a  brilliant  metallic  blue-


202


SEXUAL  DIMORPHISM


green.  On  the  ventral  surface,  the  throat,  the  lower  side  of
the  pelvics,  and  the  ventral  fin  acquire  some  black  pigment,
the  ventral  occasionally  showing  a  bluish  tinge  in  addition.
