72 
The  Physiology  of  Stock-Breeding. 
considerable  part  of  the  ovary.  The  large  follicles  are  provided 
with  a quantity  of  nutrient  fluid  containing  protein^  substances 
in  solution.  This  fluid  serves  to  nourish  the  developing  ovum 
to  which  it  is  transferred  by  a layer  of  cells  immediately 
surrounding  it.  These  cells  are  known  as  the  follicular  epithe- 
lial cells.  The  largest  follicles  are  the  ripest,  and  these  protrude 
perceptibly  from  the  ovaries  preparatory  to  discharging  the 
mature  ova  in  the  act  of  ovulation. 
Not  all  the  follicles  in  the  ovaries  reach  maturity.  A 
number  (which  probably  vary  considerably  in  different  indivi- 
duals) degenerate  during  development,  some  at  one  stage  and 
c t. 
Fig.  4. — Section  tbrough.  degenerate  follicle  (highly  magnified). 
The  ovum  and  follicular  epithelium  have  become  disintegrated  and  the  cavity  (cav.) 
is  in  process  of  being  filled  by  a loose  ingrowth  from  the  connective  tissue  wall  (c.  t.). 
some  at  another.  Even  the  very  young  follicles  not  infrequent- 
ly atrophy,  but  the  cause  is  difficult  to  determine.  Heape  has 
showffi  that  in  the  rabbit  the  process  of  degeneration  may 
sometimes  begin  with  the  ovum,  and  sometimes  with  the  folli- 
cular epithelial  cells,  but  the  flnal  result  is  the  same,  for  the 
ovum  cannot  survive  after  the  cells  which  supplied  it  with 
nourishment  have  become  disintegrated  and  functionless.  In  the 
sheep  so  far  as  my  own  observations  go,  degeneration  is  most 
liable  to  set  in  when  the  follicles  have  reached  from  about  one 
eighth  to  one  half  of  the  size  of  the  mature  follicle.  The 
1 Proteins  are  complex  nitrogenous  substances  which  in  one  form  or  another 
go  to  make  up  a very  large  portion  of  the  animal  body.  They  are  particularly 
well  represented  in  flesh  or  meat,  and  so  may  be  described  roughly  as  flesh - 
forming  substances. 
^ Heape  : “ Ovulation,”  &c.  Proc.  Royal  Soc.,  Vol.  76,  1905. 
