286 
The  Natural  History  of  the  Liver-Fluke 
Figure  6 shows  it  as  soon  as  the  change  is  completed.  We 
need  a name  by  which  to  distinguish  this  first  generation  in 
Fig.  5.  Fig.  6. 
Fig.  5,  on  the  left,  shows  the  change  of  the  embryo  into  sporocyst  just  after  it  has  entered  the  snail. 
Fig.  6,  on  the  right,  shows  a young  sporocyst  produced  by  the  change  ol  the  embryo:  /,  boring- 
tool  ; h',  eye-spots  disappearing ; k,  germinal  cells.  ^Magnified  500  times.  (Original. — A.  P..T.) 
the  snail,  and  so  will  call  it  by  its'  English  name  sporocyst , 
which  simply  means  a bag  of  germs.  This  is  literally  what  it 
becomes  as  it  grows  inside  the  snail,  its  host.  It  lives  entirely 
at  the  expense  of  the  juices  of  the  snail,  and  the  rapidity  of  its 
growth  depends  upon  the  warmth  of  the  season.  In  ordinary 
July  weather  it  will  reach  its  full  length  of  of  an  inch  by  the 
end  of  the  first  fortnight.  In  colder  weather,  however,  growth  is 
much  slower ; and  in  winter  time  very  little  progress  is  made, 
even  in  three  or  four  months. 
Figure  8 shows  a full-grown  sporocyst ; it  contains  about 
half-a-dozen  germs  of  different  sizes.  They  are  round  at  first, 
then  they  get  longer,  and  finally  take  the  outward  shape  of  a 
sack.  At  the  lower  part  of  the  figure  is  one  which  is  just  ready 
to  hatch  out,  lying  with  its  head  directed  downwards.  This 
belongs  to  the  second  generation ; it  will  be  seen  that  it  is 
different  from  the  sporocyst,  and  it  is  called  a redia,  after  the 
celebrated  anatomist  Redi.  As  soon  as  the  young  redia  is  ready 
to  leave,  it  breaks  its  way  through  the  wall  of  the  parent ; the 
wound  formed  by  its  forcing  its  way  through  immediately  closes 
up,  and  the  remaining  germs  continue  to  grow.  In  this  way 
each  sporocyst  produces  about  half  a score  of  rediae.  But  there 
is  yet  another  way  in  which  the  sporocyst  multiplies,  namely, 
by  the  division  of  one  sporocyst  into  two  across  the  middle,  as 
