Dr.  W.  Marshall  has  lately  made  a  special  study  of  the
protuberances  so  common  on  the  heads  of  birds,  J;  and  he
comes  to  the  following  conclusion:  that  with  those  species
in  which  they  are  confined  to  the  males,  they  are  developed
late  in  life;  whereas  with  those  species  in  which  they  are
common  to  the  two  sexes,  they  are  developed  at  a  very
early  period.  This  is  certainly  a  striking  confirmation  of
my  two  laws  of  inheritance.
In  most  of  the  species  of  the  splendid  family  of  the
pheasants,  the  males  differ  conspicuously  from  the  females,
and  they  acquire  their  ornaments  at  a  rather  late  period  of

*  I  have  been  assured  that  the  horns  of  the  sheep  in  North  Wales
can  always  be  felt,  and  are  sometimes  even  an  inch  in  length  at
birth.  Youatt  says  ("Cattle,"  1834,  p.  377),  that  the  prominence  of
the  frontal  bone  in  cattle  penetrates  the  cutis  at  birth,  and  that  the
horny  matter  is  soon  formed  over  it.
f  I  am  greatly  indebted  to  Prof.  Victor  Carus  for  having  made
inquiries  for  me,  from  the  highest  authorities,  with  respect  to  the
merino  sheeji  of  Saxony.  On  the  Guinea  coast  of  Africa  there  is,
however,  a  breed  of  sheep  in  which,  as  with  merinos,  the  rams  alone
bear  horns;  and  Mr.  Winwood  Reade  informs  me  that  in  one  case
observed  by  him,  a  young  ram,  born  on  Feb.  10th,  first  showed  horns
on  March  6th,  so  that  in  this  instance,  in  conformity  with  rule,  tlie
development  of  the  horns  occurred  at  a  later  period  of  life  than  in
Welsh  sheep,  in  which  both  sexes  are  horned.
X  "  Ueber  die  knochermen  Schadelhocker  der  Vogel  "  in  the  "  Nie-
derlandischen  Archiv.  fiir  Zoologie,"  Band  1,  Heft.  2,  1872.
