We  niay  now  consider  Mr.  Wallace's  arguments  in  regard


BIRDS.  515

to  the  sexual  coloration  of  birds.  He  believes  that  the
bright  tints  originally  acquired  through  sexual  selection  by
the  males  would  in  all,  or  almost  all  cases,  have  been  trans-
mitted to  the  females,  unless  the  transference  had  been
checked  through  natural  selection.  I  may  here  remind
the  reader  that  various  facts  opposed  to  this  view  have
already  been  given  under  reptiles,  amphibians,  fishes  and
lepidoptera.  Mr.  Wallace  rests  his  belief  chiefly,  but  not
exclusively,  as  we  shall  see  in  the  next  chapter,  on  the  fol-
lowing statement,*  that  when  both  sexes  are  colored  in  a
very  conspicuous  manner  the  nest  is  of  such  a  nature  as  to
conceal  the  sitting  bird;  but  when  there  is  a  marked  con-
trast of  color  between  the  sexes,  the  male  being  gay  and
the  female  dull  colored,  the  nest  is  open  and  exposes  the
sitting  bird  to  view.  This  coincidence,  as  far  as  it  goes,
certainly  seems  to  favor  the  belief  that  the  females  which
sit  on  open  nests  have  been  specially  modified  for  the  sake
of  protection;  but  we  shall  presently  see  that  there  is  an-
other and  more  probable  explanation,  namely,  that  con-
spicuous females  have  acquired  the  instinct  of  building
domed  nests  oftener  than  dull-colored  birds.  Mr.  Wallace
admits  that  there  are,  as  might  have  been  expected,  some
exceptions  to  his  two  rules,  but  it  is  a  question  whether
the  exceptions  are  not  so  numerous  as  seriously  to  invalidate
them.
