THE  ORNITHORHYNCHUS  PARADOXUS. 
225 
The  toes  on  each  of  the  four  feet  were  completely  formed,  and  terminated  by  curved 
conical  horny  claws ;  but  the  natatory  fold  of  membrane  of  the  fore  foot  had  not  the 
same  proportional  extent  as  in  the  adult,  and  the  spur  of  the  hind  foot  did  not  project 
beyond  its  socket  in  either  specimen.  In  the  smaller  one,  which  was  a  male,  it  pre- 
sented the  form  of  an  obtuse  papilla ;  while  in  the  larger  specimen,  although  a  female, 
it  was  more  plainly  developed  and  more  pointed.  This  circumstance  is  in  exact  ac- 
cordance with  the  known  laws  of  the  development  of  sexual  distinctions,  especially  of 
those  of  secondary  importance,  such  as  beards,  manes,  plumes,  horns,  tusks,  spurs,  &c., 
which  do  not  avail  in  distinguishing  the  sexes  till  towards  the  period  of  puberty.  As 
the  spur  is  the  only  obvious  distinction  of  the  sexes  in  the  full-grown  Ornithorhynchus, 
I  was  compelled  to  refer  to  the  internal  essential  organs,  in  order  to  determine  the  sex 
of  the  specimens  here  described. 
The  ventral  surface  of  the  smaller  specimen  was  carefully  examined  with  a  lens;  but 
no  trace  of  an  umbilicus  could  be  satisfactorily  determined.  In  the  very  young  or 
newly  born  Kangaroo,  a  longitudinal  linear  trace  of  the  attachment  of  the  umbilical 
vesicle  is  at  that  time  apparent,  but  it  is  rapidly  obliterated ;  as  is  probably  also  the 
case  in  the  Ornithorhynchus. 
In  the  smaller  specimen  the  intromittent  organ  projected  a  little  way  beyond  the  ex- 
crementory  orifice,  as  in  the  young  Marsupiata  ;  but  it  was  not  continuous,  as  in  them, 
with  the  anterior  margin  of  that  outlet.  In  the  larger  female  specimen  the  correspond- 
ing organ  was  visible  just  within  the  verge  of  the  opening  ;  but  this  clitoris,  remaining 
stationary  in  its  development,  is  afterwards,  as  I  have  shown  in  my  Paper  on  the  Mam- 
mary Glands*,  removed  to  a  distance  from  the  preputial  aperture  by  the  elongation  of 
the  sheath,  just  as  the  minute  spur  of  the  female  lies  concealed  at  the  bottom  of  the 
progressively  elongated  tegumentary  socket,  and  as  the  tongue  is  left  at  the  back  of  the 
oral  cavity  by  the  growth  of  the  jaws. 
The  following  were  the  anatomical  appearances  observable  in  these  young  individuals, 
so  far  as  the  rarity  of  the  specimens  would  warrant  dissection  to  be  carried. 
On  laying  open  the  abdomen  in  the  larger  specimen,  the  most  prominent  viscus  was 
the  stomach,  which  was  almost  as  large  as  in  the  adult  animal,  deriving  at  this  period 
no  assistance  from  the  preparatory  digestive  cavities,  the  cheek-pouches,  which  were  not 
yet  developed.  The  stomach  extended  in  a  curved  direction  across  the  epigastric,  and 
down  the  left  hypochondriac  region  to  the  left  iliac  region.  It  was  full  of  coagulated 
milk.  On  carefully  inspecting  the  whole  contents  with  a  lens,  no  portions  of  worms 
or  bread  could  be  detected;  which  solves  the  doubt  entertained  by  Lieut.  Maule  as  to 
whether  the  mother  nourished  this  young  one  with  the  food  which  was  given  to  her 
for  her  own  support,  or  with  secretion  afterwards  discovered  to  escape  from  the  mam- 
mary pores. 
I  took  a  portion  of  the  coagulated  substance  from  the  stomach,  and  diluted  it  with 
'  Phil.  Trans,  for  1832,  p.  525. 
