﻿64 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.98 
  

  

  an 
  infection 
  of 
  almost 
  100 
  percent 
  was 
  obtained 
  in 
  young 
  snails 
  of 
  

   approximately 
  1 
  mm. 
  in 
  length. 
  He 
  reports 
  that 
  78 
  to 
  93 
  days 
  elapse 
  

   between 
  initial 
  miracidial 
  penetration 
  and 
  cercarial 
  emergence. 
  Cer- 
  

   carial 
  shedding 
  takes 
  place 
  in 
  late 
  afternoon 
  or 
  night. 
  Stunkard 
  

   ( 
  1946) 
  reports 
  that 
  this 
  species 
  will 
  harbor 
  the 
  larval 
  stages 
  of 
  Schhfo- 
  

   soma 
  japonicum 
  as 
  far 
  as 
  the 
  mature 
  sporocyst 
  stage. 
  

  

  Oncomelania 
  nosophora 
  (Robson) 
  is 
  one 
  of 
  the 
  main 
  intermediate 
  

   hosts 
  of 
  Schistosoma 
  japonicmn 
  in 
  China 
  and 
  Japan, 
  but 
  it 
  is 
  also 
  

   known 
  to 
  serve 
  as 
  host 
  to 
  Paragonimus 
  tvestenna7ui, 
  a 
  close 
  relative 
  

   to 
  P. 
  kellicotti 
  (Chen, 
  1941). 
  This 
  may 
  indicate 
  that 
  Oncomelania 
  

   and 
  Potnatiopsis 
  have 
  a 
  similar 
  physiological 
  constitution 
  and 
  that 
  

   Pomatiopsis 
  might 
  possibly 
  be 
  capable 
  of 
  serving, 
  at 
  least 
  experi- 
  

   mentally, 
  as 
  an 
  intermediate 
  host 
  of 
  Schistosoma 
  japonicwm. 
  It 
  is 
  

   well 
  to 
  remember, 
  however, 
  that 
  these 
  two 
  species 
  of 
  Paragonimus 
  

   have 
  not 
  been 
  shown 
  to 
  be 
  the 
  same 
  or 
  distinct 
  species. 
  That 
  one 
  kind 
  

   of 
  mollusk 
  plays 
  host 
  to 
  a 
  certain 
  trematode 
  does 
  not 
  necessarily 
  mean 
  

   that 
  the 
  same 
  mollusk 
  will 
  serve 
  as 
  host 
  for 
  a 
  closely 
  related 
  species 
  of 
  

   trematode. 
  For 
  example, 
  one 
  species 
  of 
  Schistosoma 
  is 
  carried 
  by 
  

   OncoTYielania 
  (a 
  gill-bearing 
  Streptoneura) 
  , 
  another 
  species 
  by 
  Bulinus 
  

   (a 
  lung-bearing 
  Euthyneura). 
  Care 
  must 
  be 
  taken 
  in 
  the 
  use 
  of 
  

   specificity 
  homologies. 
  Systematic 
  relationships 
  in 
  mollusks 
  are 
  no 
  

   key 
  to 
  the 
  solution. 
  Of 
  primary 
  importance, 
  however, 
  is 
  the 
  combina- 
  

   tion 
  of 
  suitable 
  physiological 
  environment 
  and 
  the 
  ideal 
  habitat 
  or 
  

   external 
  environment 
  of 
  the 
  snail. 
  From 
  this 
  latter 
  standpoint, 
  

   Pomatiopsis 
  lapidaria 
  offers 
  the 
  most 
  suitable 
  conditions 
  in 
  North 
  

   America 
  for 
  the 
  introduction 
  of 
  Schistosoma 
  japomeum. 
  

  

  Our 
  present 
  knowledge 
  of 
  molluscan 
  host 
  specificity 
  is 
  very 
  frag- 
  

   mentary. 
  The 
  final 
  answer 
  will 
  probably 
  come 
  from 
  a 
  physiological 
  

   analysis 
  of 
  each 
  implicated 
  molluscan 
  species. 
  Miracidia 
  of 
  the 
  

   trematode 
  must 
  not 
  only 
  be 
  attracted 
  to 
  the 
  snail, 
  but 
  upon 
  entering 
  

   must 
  develop 
  successfully 
  to 
  the 
  cercarial 
  stages. 
  The 
  miracidia 
  of 
  

   Schistosoma 
  japonicwm 
  in 
  the 
  Philippines 
  are 
  not 
  in 
  the 
  least 
  attracted 
  

   to 
  thiarid 
  or 
  lymnaeid 
  snails, 
  but 
  they 
  do 
  make 
  rapid 
  advances 
  toward 
  

   Oncomelania 
  quadrasi 
  and 
  several 
  species 
  of 
  Syncera. 
  O. 
  quadrasi 
  

   is 
  the 
  only 
  known 
  intermediate 
  host 
  of 
  this 
  trematode 
  in 
  that 
  area, 
  but 
  

   several 
  hundred 
  specimens 
  of 
  Syncera 
  examined 
  from 
  the 
  endemic 
  re- 
  

   gion 
  of 
  Palo, 
  Leyte, 
  showed 
  no 
  signs 
  of 
  infection, 
  nor 
  was 
  an 
  attempt 
  

   to 
  infect 
  three 
  species 
  of 
  "attractive" 
  Syncera 
  successful. 
  Chinese 
  

   species 
  of 
  Syncera 
  collected 
  from 
  the 
  same 
  spot 
  as 
  infected 
  Oncome- 
  

   lania 
  nosophora 
  always 
  gave 
  negative 
  results. 
  That 
  miracidia 
  are 
  

   attracted 
  to 
  Syncera 
  is 
  perhaps 
  correlated 
  with 
  the 
  fact 
  that 
  this 
  snail 
  

   has 
  very 
  much 
  the 
  same 
  amphibious 
  habits 
  as 
  Oncamelania. 
  The 
  same 
  

   commensal 
  ciliates 
  are 
  found 
  abundantly 
  in 
  the 
  mantle 
  cavity 
  of 
  these 
  

   two 
  genera 
  but 
  are 
  absent 
  from 
  snails 
  that 
  have 
  no 
  attraction 
  for 
  

   japonicum 
  miracidia. 
  

  

  