§  Another  ^"eat  authority  with  respect  to  this  class.  Prof.  Thorell,  of  Upsala
("  On  European  Spiders,"  186S-1870,  part  i,  p.  205),  speaks  as  if  female  spiders
were  jcenerally  commoner  than  the  males.
II  See,  on  this  subject,  :Mr.  O.  P.  Cambridge,  as  quoted  in  "  Quarterly  Jour-
nal of  Science,"  1868.  p.  429.
^"Beitrage  zur  Parthenogenesis,"  p.  174.
288  THE  DESCENT  OF  MAN.
s])ecies  in  the  latter  genus,  63  specimens  cauglittLe  same  day  included
57  males;  but  he  suggests  that  this  preponderance  may  be  due  to
some  unknown  difference  in  the  habits  of  the  two  sexes.  With  one
of  the  higher  Brazilian  crabs,  namely,  a  Gelasimus,  Fritz  Mtiller
found  the  males  to  be  more  numerous  than  the  females.  According
to  the  large  experience  of  Mr.  C.  Spence  Bate,  the  reverse  seems  to
be  the  case  with  six  common  British  crabs,  the  names  of  which  he
has  given  me.
The  Proportion  of  the  Sexes  in  Relation  to  Natural
Selection. — There  is  reason  to  suspect  that  in  some  cases
man  has  by  selection  indirectly  influenced  his  own  sex-
producing  powers.  Certain  women  tend  to  produce  during
their  whole  lives  more  children  of  one  sex  than  of  the
other;  and  the  same  holds  good  of  many  animals^  for
instance,  cows  and  horses;  thus  Mr.  Wright,  of  Yeldersley
House,  informs  me  that  one  of  his  Arab  mares,  though  put
seven  times  to  different  horses,  produced  seven  fillies.
Though  I  have  very  little  evidence  on  this  head,  analogy
would  lead  to  the  belief  that  the  tendency  to  produce
either  sex  would  be  inherited  like  almost  every  other
peculiarity,  for  instance,  that  of  producing  twins;  and  con-
cerning the  above  tendency  a  good  authority,  Mr.  J.
