294 
The  Natural  History  of  the  Liver-Fluke 
destined  to  enter  the  sheep)  will,  on  leaving  their  host,  form 
their  cysts  on  the  grass  in  the  places  where  they  will  have  the 
best  chance  of  being  transferred  to  the  sheep  grazing  on  the 
ground. 
Man  himself  sometimes  serves  as  host  to  the  liver-fluke,  and 
in  this  case  the  cysts  containing  the  young  flukes  are  probably 
eaten  with  watercress. 
Growth  and  Duration  of  Life  of  the  Fluke  in  the  Sheep. — From 
observations  which  I need  not  describe  here,  as  they  have  been 
given  in  a former  Report,*  it  appears  probable  that  at  least  six 
weeks  elapse  from  the  time  the  fluke  is  swallowed  by  the  sheep 
before  the  parasite  becomes  adult  and  begins  to  produce  eggs. 
A very  great  increase  in  bulk  occurs,  for  when  the  young  fluke 
is  introduced  it  is  perhaps  only 
^jth  of  an  inch  in  length, 
whereas  the  adult  fluke  reaches 
an  inch  or  an  inch  and  a 
third.  A change  occurs  also 
in  the  form  of  the  body,  as 
will  be  seen  from  Figs.  14, 
15,  16,  and  17  ; it  is  due  to 
the  more  rapid  growth  of  the 
hind  part  of  the  body,  which 
contains  the  reproductive 
organs  (Fig.  18). 
Of  great  practical  import- 
ance is  the  question  how  long 
the  fluke  remains  alive  within 
the  sheep.  For  it  will  depend 
upon  the  length  of  this  period 
whether  or  not  it  is  worth 
while  trying  to  keep  the  in- 
fected animals  alive  until  the 
life  of  the  fluke  has  reached 
its  natural  limit. 
The  liver-fluke  is  supposed 
by  some  to  pass  out  of  the 
sheep  at  the  beginning  of 
summer.  If  this  were  the 
case,  its  life  would  not  last 
more  than  three-quarters  of 
a year.  Gerlach  states  that 
the  fluke  always  passes  out  in  the  months  of  June  and  July, 
but  Pech  f says  that  he  has  seen  flukes  pass  out  from  rotten 
* ‘Journal  of  the  Itoyal  Agricultural  Society,’  1S81,  p.  25. 
f ‘ Der  Thier-arzt,’  1873,  p.  87. 
Figs.  14,  15,  16. 
Three  young  flukes  from  the  liver  of  a sheep  to 
show  the  change  in  lorm  during  growth.  All 
are  magnified  7J-  times.  Fig.  14  (on  the  left) 
represents  the  smallest  fluke  I have  ever  found 
in  a sheep ; it  was  only  ^ of  an  inch  in  length. 
Fig.  15  (in  the  centre)  shows  the  shape  of  a 
fluke  *-  of  an  inch  loilg,  and  Fig.  16  (on  the 
right)  shows  a fluke  which  lias  reached  ‘ of  the 
full ‘length  of  the  adult  animal.  (Original. — 
A.  P.  T.) 
