﻿6 
  PROCEEDINGS 
  OF 
  THE 
  NATIONAL 
  MUSEUM 
  vol.67 
  

  

  tain. 
  In 
  the 
  case 
  of 
  Ascaris 
  decipiens 
  (=Porrocaecum 
  decipiens) 
  

   of 
  the 
  Alaskan 
  seal, 
  the 
  source 
  of 
  infection 
  with 
  this 
  parasite 
  accord- 
  

   ing 
  to 
  Stiles 
  and 
  Hassall 
  (1899) 
  is 
  to 
  be 
  found 
  in 
  certain 
  fish 
  that 
  

   constitute 
  part 
  of 
  the 
  food 
  of 
  the 
  definitive 
  host. 
  Stiles 
  and 
  Hassall 
  

   (1899) 
  say 
  that 
  immature 
  ascarids, 
  representing 
  various 
  stages 
  inter- 
  

   mediate 
  between 
  the 
  adult 
  forms 
  of 
  Ascaris 
  decipiens 
  and 
  the 
  so- 
  

   called 
  Ascaris 
  capsularia, 
  which 
  is 
  a 
  collective 
  name 
  applied 
  to 
  larval 
  

   nematodes 
  found 
  encysted 
  in 
  various 
  species 
  of 
  fish, 
  occur 
  in 
  the 
  

   stomach 
  of 
  seals, 
  and 
  that 
  this 
  suggests 
  that 
  these 
  animals 
  acquire 
  

   the 
  infection 
  with 
  Porrocaecum 
  decipiens 
  as 
  a 
  result 
  of 
  eating 
  in- 
  

   fected 
  fish. 
  Although 
  Stiles 
  and 
  Hassall 
  did 
  not 
  carry 
  out 
  any 
  

   feeding 
  experiments, 
  they 
  report 
  finding 
  encysted 
  ascarids 
  in 
  the 
  

   Alaskan 
  pollock 
  and 
  the 
  Pacific 
  cod, 
  which 
  were 
  identical 
  with 
  the 
  

   youngest 
  forms, 
  presumably 
  of 
  Porrocaecum 
  decipiens, 
  found 
  in 
  

   seals. 
  Since 
  these 
  fishes 
  are 
  known 
  to 
  be 
  eaten 
  by 
  seals, 
  Stiles 
  and 
  

   Hassall 
  conclude 
  with 
  a 
  fair 
  degree 
  of 
  certainty 
  that 
  the 
  definitive 
  

   host 
  acquires 
  the 
  infection 
  as 
  a 
  result 
  of 
  eating 
  the 
  intermediate 
  

   host. 
  So 
  far 
  as 
  concerns 
  Ascaris 
  incisa 
  it 
  was 
  suggested 
  by 
  Leuckart 
  

   (1876) 
  that 
  it 
  is 
  the 
  larval 
  form 
  of 
  Ascaris 
  depressa 
  (=Porrocaecum 
  

   depressum), 
  a 
  nematode 
  that 
  occurs 
  in 
  various 
  birds 
  of 
  prey 
  such 
  

   as 
  hawks 
  and 
  owls. 
  Leuckart's 
  view 
  has 
  been 
  commonly 
  accepted 
  

   by 
  helminthologists, 
  although 
  no 
  experimental 
  evidence 
  has 
  been 
  

   obtained 
  to 
  prove 
  this 
  relationship. 
  

  

  The 
  occurrence 
  of 
  encysted 
  Porrocaecum 
  larvae 
  in 
  mammals 
  sug- 
  

   gests 
  a 
  relationship 
  between 
  the 
  intermediate 
  and 
  the 
  unknown 
  de- 
  

   finitive 
  hosts 
  similar 
  to 
  that 
  described 
  by 
  Stiles 
  and 
  Hassall 
  (1899) 
  for 
  

   Porrocaecum 
  decipiens. 
  The 
  unknown 
  definitive 
  hosts 
  in 
  the 
  cases 
  

   reported 
  by 
  the 
  present 
  writer 
  and 
  by 
  others 
  are 
  in 
  all 
  probability 
  

   birds, 
  presumably 
  hawks 
  and 
  owls, 
  and 
  other 
  flesh-eating 
  birds. 
  

   Two 
  species 
  of 
  Poi^rocaecum 
  from 
  hawks 
  are 
  represented 
  in 
  the 
  Hel- 
  

   minthological 
  Collections 
  of 
  the 
  United 
  States 
  National 
  Museum. 
  

   One 
  species 
  is 
  from 
  Circus 
  hudsonicus 
  and 
  the 
  other 
  is 
  from 
  Falco 
  

   columbarius, 
  both 
  from 
  Fishers 
  Island, 
  New 
  York. 
  The 
  form 
  from 
  

   Circus 
  hudsonicus 
  has 
  a 
  very 
  small 
  intestinal 
  cecum. 
  An 
  American 
  

   species 
  of 
  Porrocaecum 
  is 
  described 
  by 
  Smith, 
  Fox, 
  and 
  White 
  

   (1908) 
  as 
  Ascaris 
  ardea 
  {=Porrocaecum 
  retieidatum) 
  according 
  to 
  

   Baylis 
  and 
  Daubney 
  (1922), 
  from 
  a 
  North 
  American 
  blue 
  heron 
  

   (Ardea 
  herodias). 
  Smith, 
  Fox, 
  and 
  White 
  fail 
  to 
  mention 
  the 
  ven- 
  

   triculus 
  and 
  the 
  esophageal 
  bulb. 
  Baylis 
  and 
  Daubney 
  (1922) 
  are 
  

   convinced, 
  however, 
  that 
  the 
  species 
  described 
  by 
  Smith, 
  Fox, 
  and 
  

   White 
  is 
  a 
  synonym 
  of 
  Ascaris 
  reticulata 
  von 
  Linstow 
  1899 
  (^Pw- 
  

   rocaecv/m 
  reticulatum) 
  . 
  According 
  to 
  the 
  former 
  writers 
  this 
  species 
  

   has 
  a 
  well-developed 
  intestinal 
  cecum 
  and 
  a 
  less 
  conspicuous 
  ven- 
  

   triculus, 
  which 
  they 
  describe 
  as 
  short 
  and 
  oblong. 
  While 
  the 
  larval 
  

  

  