and  the  Prevention  of  Rot.  293 
covered  by  them,  and  they  were  found  abundantly  on  the 
flooded  ground. 
On  returning  three  weeks  later  to  the  same  ditch  I was  unable 
to  find  a single  example  alive  in  the  water.  As  I had  not  suffi- 
cient leisure  on  this  visit  to  examine  the  ground  near  the  ditch, 
I returned  for  the  purpose  of  doing  so  eight  days  later.  There 
had  been  dry  weather  since  the  flood,  but  early  that  morning 
heavy  rain  bad  fallen,  and  I found  numbers  of  specimens  of 
L.  truncatulus  on  the  gravel  of  a path  near  the  ditch,  and 
these  seemed  to  have  crawled  out  of  the  grass  when  revived  by 
the  rain.  At  the  roots  of  the  grass,  all  along  the  margin  of  the 
ditch,  others  were  found  in  abundance.  Some  few  shells  were 
quite  empty,  but  the  majority  contained  the  dried  remains  of 
the  snail,  which  had  shrunk  far  back  into  the  spire  of  the  shell. 
Most  of  these  appeared  to  be  quite  dead,  but  were,  however, 
merely  dormant,  for  on  placing  them  in  water  the  tissues 
imbibed  moisture  and  assumed  their  natural  bulk  ; and  after 
a few  hours  the  snails  had  regained  their  full  activity,  and  were 
seemingly  none  the  worse  for  their  prolonged  drying  up. 
To  test  the  power  of  resisting  drought  possessed  by  the  snail, 
I collected  a number  of  specimens,  and  placed  them  in  an  open 
vessel  on  a shelf  in  a dry  laboratory,  in  a position  where  the 
sun  fell  upon  them  for  an  hour  or  so  daily.  I found  that  rather 
more  than  half  of  them  withstood  twenty-six  days  of  this 
treatment,  and  some  few  revived  after  more  than  six  weeks. 
That  the  snails  can  live  on  moist  ground,  quite  away  from  any 
quantity  of  water,  for  considerable  periods,  is  sufficiently  proved 
by  the  fact  that  I have  kept  them  alive  for  eleven  weeks  on 
moist  grass  and  moss,  even  when  infested  with  the  larval  forms 
of  the  liver-fluke. 
It  is  clear,  therefore,  that  the  kind  of  snail  under  consideration 
may  be  brought  in  great  quantities  by  floods,  and  may  be  left 
on  the  fields  when  the  waters  pass  away.  The  snails  thus  left 
continue  to  wander  and  feed,  so  long  as  the  bottom  of  the  grass 
remains  moist.  Their  numbers  are  recruited  from  surrounding 
ditches  and  streams.  Even  on  land  tvhich  is  not  liable  to  floods 
this  snail  may  exist  in  large  quantities,  having  crawled  from  the 
ditches,  ponds,  streams,  and  marshy  spots,  through  the  moist 
grass.  A drought  may  render  the  snail  dormant,  but,  unless 
continued  too  long,  it  revives  at  the  first  shower  of  rain. 
If  there  are  fluke-eggs  on  the  ground,  the  embryos  hatched 
out  of  these  will  gain  entrance  to  the  Limnceus  truncatulus 
living  in  wet  places.  Owing  to  the  habit  which  this  par- 
ticular snail  has  of  living  so  much  out  of  the  water,  either  on 
the  banks  of  ditches,  or  further  away  towards  the  centre  of 
the  fields  if  they  are  damp  enough,  the  cercariae  (the  larval  forms 
