70 
The  Physiology  of  Stock-Breeding. 
have  observed,  only  one  ovum  is  usually  discharged  at  ovula- 
tion, this  being  apparent  from  the  single  ruptured  follicle* 
remaining  in  one  of  the  ovaries.  In  the  mare  also,  it  is  usual 
for  only  one  follicle  to  rupture  at  a time,  though  of  course,  in 
both  these  animals,  twins  are  occasionally  produced.  In  the 
sheep,  however,  in  which  twins  and  triplets  are  not  uncommon, 
I have  frequently  found  two  and  sometimes  three  recently 
discharged  follicles  in  the  ovaries  during  the  tupping  season, 
but  even  in  this  animal  a single  discharged  follicle  is,  in  my 
i.  f. 
Fig.  2.— Section  through  Graafian  follicle  of  ovary  (highly  magnified), 
c.  t..  connective  tissue  forming  outside  wall  of  follicle ; /.  e.,  follicular  epithelium  ; 
1.  /.,  liquor  folliculi  occupying  cavity  ; o.,  ovum  ; ov.  t.,  tissue  forming  ground  substance 
of  ovary. 
experience,  more  usual,  especially  among  hill  sheep.  In  view 
of  these  facts  it  is  clear  that  the  ewe  is  a more  important  factor 
in  twin  production  than  the  tup,  for  whereas  the  number  of  ova 
ready  for  fertilisation  at  a heat  period  is  very  limited,  the 
number  of  spermatozoa  is  innumerable.  I have  seen  sperma- 
tozoa present  within  the  lumina  or  hollow  cavities  of  the 
uterine  glands  and  along  the  edge  of  the  uterine  cavity  in 
extraordinary  abundance  on  the  day  ’following  service,  so  that 
it  seems  inconceivable  in  such  cases  that  any  ova  entering  that 
organ  could  escape  fertilisation  through  a deficiency  in  the 
number  of  spermatozoa. 
* The  little  sacs  or  bags  which  contain  the  developing  ova  in  the  ovaries  are 
called  Graafian  follicles  (see  Fig.  2). 
