﻿CESTODE 
  PARASITES 
  OF 
  FISHES— 
  LINTON. 
  449 
  

  

  shark 
  {Prionace 
  glaiica) 
  which 
  appears 
  to 
  be 
  identical 
  with 
  this 
  spe- 
  

   cies, 
  at 
  least 
  in 
  the 
  character 
  and 
  disposition 
  of 
  the 
  hooks 
  on 
  the 
  

   proboscides, 
  which 
  I 
  find 
  to 
  be 
  one 
  of 
  the 
  safest 
  criteria 
  iu 
  determining 
  

   identities 
  in 
  the 
  Tetrarhynchidii\ 
  Two 
  specimens 
  were 
  fonnd 
  in 
  the 
  

   blue 
  shark 
  August 
  5, 
  1889, 
  at 
  Woods 
  Holl, 
  Massachusetts. 
  They 
  were 
  

   associated 
  with 
  Orygmatohothrium 
  angustum 
  and 
  Antliohothrlum 
  Jacini- 
  

   atiim. 
  

  

  Dimensions 
  of 
  alcoholic 
  specimens: 
  Length 
  of 
  head 
  and 
  neck, 
  0.85 
  

   mm. 
  in 
  one, 
  1 
  in 
  the 
  other; 
  length 
  of 
  bothrinm, 
  0.24; 
  breadth 
  of 
  head, 
  

   0.36; 
  diameter 
  of 
  neck, 
  0.27; 
  length 
  of 
  last 
  (eighth) 
  segment, 
  0.54; 
  

   wLole 
  length 
  of 
  each 
  specimen, 
  2.5. 
  Color 
  faint 
  reddish 
  brown 
  or 
  flesh 
  

   color. 
  The 
  posterior 
  segments 
  are 
  loosely 
  attached 
  and 
  evidently 
  be- 
  

   came 
  detached 
  before 
  maturity. 
  A 
  number 
  of 
  free 
  proglottides 
  which 
  

   had 
  been 
  placed 
  in 
  a 
  vial 
  with 
  specimens 
  of 
  0. 
  angustum 
  are 
  evidently 
  

   Rhynchobothrium 
  segments 
  and 
  presumably 
  belong 
  to 
  this 
  species. 
  

   One 
  of 
  them 
  is 
  represented 
  in 
  Fig. 
  8. 
  If 
  they 
  are 
  in 
  truth 
  specimens 
  

   of 
  this 
  species 
  they 
  have 
  increased 
  in 
  length 
  enormously 
  as 
  compared 
  

   with 
  those 
  which 
  are 
  still 
  attached 
  to 
  the 
  strobile. 
  

  

  Dimensions 
  of 
  one 
  of 
  these 
  free 
  proglottides 
  (alcoholic): 
  Length, 
  2.8 
  

   mm.; 
  breadth 
  near 
  anterior 
  end, 
  0.56; 
  breadth 
  at 
  reproductive 
  aper- 
  

   tnre, 
  0.56; 
  breadth 
  near 
  posterior 
  end, 
  0,3. 
  

  

  Proglottis 
  slipper-shaped, 
  round 
  at 
  anterior 
  end, 
  slightly 
  constricted 
  

   in 
  front 
  of 
  reproductive 
  aperture 
  about 
  middle, 
  bluntly 
  rounded 
  and 
  

   slightly 
  narrowed 
  posteriorly; 
  reproductive 
  aperture 
  on 
  lateral 
  margin 
  

   near 
  posterior 
  third, 
  in 
  broad 
  shallow 
  cloaca; 
  vitellaria 
  narrow 
  along 
  

   each 
  lateral 
  margin 
  through 
  nearly 
  whole 
  length; 
  testicular 
  masses 
  in 
  

   anterior 
  half; 
  ovaries 
  two, 
  united 
  by 
  narrow 
  part 
  about 
  halfway 
  between 
  

   reproductive 
  aperture 
  and 
  posterior 
  end; 
  vagina 
  short, 
  curved, 
  opening 
  

   beside 
  and 
  behind 
  cirrus; 
  cirrus 
  bulb 
  oval, 
  inclined 
  inward 
  and 
  forward. 
  

  

  The 
  crenulate 
  ma' 
  gins 
  agree 
  with 
  what 
  was 
  observed 
  on 
  segments 
  

   attached 
  to 
  strobile. 
  Analogy 
  with 
  R. 
  bulbifer, 
  whose 
  proglottides 
  

   grow 
  after 
  separation 
  from 
  strobile, 
  favor 
  the 
  theory 
  that 
  these 
  segments 
  

   belong 
  to 
  R. 
  ten 
  ulspine. 
  Length 
  of 
  longest 
  fragment, 
  22 
  mm. 
  (the 
  length 
  

   of 
  a 
  strobile 
  must 
  be 
  very 
  considerably 
  greater 
  than 
  this) 
  ; 
  length 
  of 
  

   bothrinm, 
  0.55; 
  breadth 
  of 
  bothrium, 
  0.4; 
  length 
  of 
  head 
  and 
  neck, 
  1.4; 
  

   diameter 
  of 
  neck, 
  0.4; 
  length 
  of 
  contractile 
  bulbs, 
  0.35; 
  length 
  of 
  last 
  

   segments, 
  2.4; 
  breadth 
  of 
  last 
  segments, 
  0.6. 
  

  

  Dimensions 
  of 
  another 
  specimen, 
  alcoholic: 
  Length 
  of 
  bothrium, 
  0.45 
  

   mm.; 
  length 
  of 
  proboscis, 
  0.9; 
  diameter 
  of 
  proboscis 
  at 
  base, 
  including 
  

   hooks, 
  0.045; 
  diameter 
  of 
  proboscis 
  at 
  apex, 
  including 
  hooks, 
  0.035; 
  

   length 
  of 
  largest 
  hooks, 
  0.012. 
  

  

  In 
  one 
  specimen 
  two 
  of 
  the 
  proboscides 
  had 
  been 
  extended 
  along 
  with 
  

   0.3 
  mm. 
  of 
  the 
  sheath. 
  

  

  The 
  scolex 
  and 
  strobile 
  bear 
  some 
  resemblance 
  to 
  those 
  of 
  R. 
  agile, 
  

   but 
  the 
  character 
  of 
  the 
  hooks 
  on 
  the 
  proboscides 
  is 
  quite 
  different 
  in 
  the 
  

   two 
  species. 
  

  

  Proc. 
  2sr. 
  M. 
  vol. 
  XX 
  29 
  

  

  