﻿540 
  rnocEEDlXGS 
  of 
  the 
  XATTOXAL 
  MFSEFM. 
  vol 
  xx 
  

  

  placed 
  with 
  let'ereiu'e 
  to 
  each 
  other, 
  with 
  their 
  walls, 
  in 
  section 
  exposed, 
  

   contiguous. 
  The 
  vitellaria 
  also 
  extend 
  forward 
  on 
  eacli 
  side 
  of 
  the 
  

   uterine 
  folds. 
  

  

  Transverse 
  and 
  longitudinal 
  sections 
  reveal 
  the 
  following 
  facts 
  with 
  

   regard 
  to 
  the 
  arrangement 
  of 
  the 
  vessels 
  of 
  the 
  excretory 
  and 
  digest- 
  

   ive 
  systems: 
  A 
  plexus 
  of 
  anastomosing 
  vessels 
  is 
  seen 
  in 
  front 
  of 
  the 
  

   pharynx 
  (Fig. 
  8), 
  from 
  which 
  the 
  two 
  lateral 
  vessels 
  of 
  the 
  intestine 
  

   are 
  soon 
  differentiated. 
  The 
  pharynx 
  follows 
  tlie 
  oral 
  sucker 
  immedi- 
  

   ately 
  and 
  opens 
  into 
  a 
  short 
  (esophagus 
  (Fig. 
  10) 
  which 
  extends 
  poste- 
  

   riorly 
  for 
  a 
  short 
  distance 
  in 
  a 
  blind 
  i)rolongation, 
  anteriorly 
  it 
  eom- 
  

   niunicates 
  with 
  the 
  two 
  intestinal 
  vessels. 
  (Fig. 
  9.) 
  The 
  remaining 
  

   vessels 
  of 
  the 
  plexus, 
  whi(di 
  I 
  take 
  to 
  represent 
  the 
  excretory 
  system, 
  

   (continue 
  as 
  several 
  vessels 
  for 
  some 
  distance 
  back 
  of 
  the 
  pharynx, 
  but 
  

   appear 
  as 
  only 
  two 
  ])rincipal 
  lateral 
  vessels 
  in 
  sections 
  about 
  the 
  ante- 
  

   rior 
  limit 
  of 
  the 
  ventral 
  sucker. 
  In 
  sections 
  through 
  the 
  ventral 
  sucker 
  

   and 
  testes 
  the 
  longitudinal 
  vessels 
  are 
  much 
  compressed 
  and 
  crowded 
  

   against 
  the 
  body 
  wall. 
  In 
  the 
  posterior 
  half 
  of 
  the 
  body 
  the 
  intestinal 
  

   tracts 
  occupy 
  the 
  greater 
  part 
  of 
  the 
  space, 
  are 
  compressed 
  laterally, 
  

   and 
  contain 
  a 
  very 
  dark-brown 
  or 
  black 
  food, 
  material. 
  The 
  w^alls 
  of 
  

   the 
  intestine 
  are 
  very 
  much 
  folded, 
  even 
  amounting 
  almost 
  to 
  distinct 
  

   rami, 
  and 
  are 
  beset 
  with 
  distinct 
  villi, 
  0.041 
  mm. 
  in 
  depth. 
  The 
  excre- 
  

   tory 
  vessels 
  are 
  indistinct 
  in 
  sections 
  of 
  the 
  middle 
  of 
  the 
  body; 
  there 
  

   is, 
  however, 
  a 
  very 
  prominent 
  posterior 
  vessel 
  which 
  terminates 
  in 
  a 
  

   distinct 
  pore. 
  

  

  The 
  vitellaria 
  in 
  the 
  serial 
  sections 
  begin 
  as 
  small 
  brownish-yellow 
  

   tubular 
  masses 
  in 
  the 
  vicinity 
  of 
  the 
  testes, 
  where 
  they 
  are 
  arranged 
  

   laterally 
  near 
  the 
  periphery. 
  Behind 
  the 
  testes 
  they 
  are 
  more 
  abun- 
  

   dant, 
  but 
  nowhere 
  very 
  voluminous. 
  

  

  The 
  body 
  wall 
  is 
  very 
  thick 
  and 
  muscular, 
  and 
  the 
  body 
  cavity 
  back 
  

   of 
  the 
  testes 
  mainly 
  occupied 
  by 
  the 
  very 
  large 
  intestinal 
  vessels. 
  

  

  31. 
  DISTOMUM 
  species 
  (larva). 
  

   (Plates 
  Lill, 
  tiers. 
  12, 
  13; 
  LI\', 
  ii.n- 
  1.) 
  

  

  No. 
  4871, 
  U.S.lSr.M. 
  From 
  pericardium 
  of 
  Htizostedion 
  eanaflevse, 
  

   Washington, 
  Pennsylvania 
  (market), 
  tish 
  from 
  Lake 
  Frie: 
  collected 
  

   March 
  7, 
  1891. 
  

  

  These 
  specimens 
  are 
  small, 
  immature, 
  in 
  capsules, 
  0..'>5 
  to 
  0.8,") 
  mm. 
  

   in 
  diameter. 
  Diameter 
  of 
  oral 
  sucker, 
  0.094 
  mm.; 
  diameter 
  of 
  ventral 
  

   sucker, 
  0.055 
  mm. 
  The 
  specimens 
  are 
  too 
  immature 
  for 
  identification. 
  

  

  Sections 
  of 
  a 
  cyst 
  with 
  its 
  contained 
  eml)ryo 
  show 
  that 
  the 
  outer 
  

   half 
  of 
  the 
  wall 
  of 
  the 
  cyst 
  is 
  built 
  up 
  of 
  concentric 
  layers 
  of 
  connect- 
  

   ive 
  tissue 
  secreted 
  from 
  the 
  tissues 
  of 
  the 
  host; 
  the 
  inner 
  half 
  of 
  the 
  

   wall 
  consists 
  of 
  an 
  embryonic 
  envelope, 
  which 
  communicates 
  with 
  the 
  

   embryo 
  by 
  a 
  special 
  duct. 
  The 
  o])ening 
  of 
  this 
  duct, 
  as 
  relates 
  to 
  

   the 
  embryo, 
  is 
  ventral, 
  and 
  is 
  situated 
  a 
  little 
  way 
  back 
  of 
  the 
  ventral 
  

   sucker. 
  

  

  