﻿FRESH-WATER 
  TRICLADS 
  OF 
  ALASKA 
  — 
  ^KENK 
  179 
  

  

  and 
  a 
  pair 
  of 
  rounded 
  auricles 
  protruding 
  both 
  anteriorly 
  and 
  later- 
  

   ally. 
  No 
  distinct 
  adhesive 
  or 
  grasping 
  organ 
  is 
  developed. 
  There 
  is 
  

   a 
  gentle 
  narrowing 
  of 
  the 
  head 
  (neck) 
  behind 
  the 
  auricles. 
  Behind 
  

   the 
  head, 
  the 
  width 
  of 
  the 
  body 
  gradually 
  increases 
  until 
  the 
  greatest 
  

   width 
  is 
  reached. 
  The 
  posterior 
  end 
  is 
  bluntly 
  pointed. 
  

  

  The 
  body 
  lacks 
  pigment, 
  being 
  white 
  except 
  for 
  the 
  contents 
  of 
  

   the 
  intestine, 
  which 
  may 
  show 
  through 
  the 
  body 
  wall. 
  

  

  There 
  are 
  two 
  principal 
  eyes. 
  The 
  distance 
  between 
  them 
  amounts 
  

   to 
  about 
  one-third 
  the 
  width 
  of 
  the 
  head 
  at 
  the 
  level 
  of 
  the 
  eyes. 
  

   The 
  distance 
  of 
  each 
  eye 
  from 
  the 
  frontal 
  margin 
  is 
  equal 
  to, 
  or 
  

   slightly 
  larger 
  than, 
  the 
  distance 
  from 
  the 
  lateral 
  margin. 
  Additional, 
  

   supernumerary, 
  eyes 
  were 
  seen 
  in 
  a 
  few 
  individuals 
  at 
  short 
  distances 
  

   either 
  anterior 
  or 
  posterior 
  to 
  the 
  principal 
  eyes. 
  

  

  The 
  species 
  bears 
  a 
  striking 
  resemblance 
  to 
  a 
  European 
  species, 
  

   Dendrocoelum 
  nausicaae 
  Schmidt 
  of 
  the 
  Balkan 
  Peninsula. 
  It 
  is 
  

   generally 
  associated 
  with 
  another 
  triclad 
  inhabiting 
  the 
  same 
  streams 
  

   in 
  Alaska, 
  Phagocata 
  nivea, 
  from 
  which 
  it 
  may 
  be 
  distinguished 
  by 
  

   its 
  larger 
  size 
  and 
  by 
  the 
  position 
  of 
  the 
  eyes. 
  

  

  A 
  distinct 
  adhesive 
  organ 
  is 
  not 
  seen 
  in 
  living 
  animals. 
  In 
  histologi- 
  

   cal 
  sections, 
  a 
  transverse 
  band, 
  pierced 
  by 
  numerous 
  openings 
  of 
  

   eosinophilic 
  glands, 
  is 
  found 
  below 
  the 
  frontal 
  margin 
  of 
  the 
  head. 
  

   The 
  nature 
  of 
  the 
  glands 
  and 
  the 
  local 
  differentiation 
  of 
  the 
  epithelium 
  

   correspond 
  entirely 
  to 
  the 
  structure 
  of 
  the 
  submarginal 
  adhesive 
  zone 
  

   which 
  is 
  seen 
  in 
  this 
  species, 
  as 
  well 
  as 
  in 
  other 
  triclads, 
  bordering 
  the 
  

   lateral 
  margins 
  of 
  the 
  body. 
  The 
  frontal 
  adhesive 
  area 
  may, 
  therefore, 
  

   be 
  interpreted 
  as 
  an 
  extension 
  of 
  the 
  lateral 
  adhesive 
  zone. 
  It 
  is 
  

   somewhat 
  wider 
  than 
  the 
  lateral 
  one 
  and 
  has 
  no 
  muscular 
  differen- 
  

   tiations 
  such 
  as 
  are 
  typical 
  of 
  true 
  grasping 
  organs. 
  The 
  continuity 
  

   of 
  the 
  two 
  zones 
  is 
  interrupted 
  by 
  a 
  short 
  gap 
  on 
  each 
  side 
  of 
  the 
  

   head 
  below 
  the 
  auricle. 
  

  

  The 
  internal 
  muscle 
  zone 
  of 
  the 
  pharynx 
  consists 
  of 
  a 
  layer 
  of 
  inter- 
  

   mingled 
  circular 
  and 
  longitudinal 
  fibers. 
  This 
  character 
  places 
  the 
  

   species 
  in 
  the 
  family 
  Dendrocoelidae. 
  The 
  anterior 
  intestinal 
  trunk 
  

   bears 
  a 
  fairly 
  large 
  number, 
  21 
  to 
  24 
  pairs, 
  of 
  lateral 
  branches, 
  or 
  

   diverticula. 
  

  

  Of 
  a 
  total 
  of 
  eight 
  individuals 
  of 
  this 
  species 
  at 
  my 
  disposal, 
  five 
  

   were 
  young, 
  two 
  showed 
  primordia 
  of 
  genital 
  structures, 
  and 
  only 
  one 
  

   had 
  the 
  principal 
  parts 
  of 
  the 
  reproductive 
  system 
  developed, 
  though 
  

   not 
  fully 
  differentiated 
  histologically. 
  The 
  description 
  of 
  the 
  genital 
  

   organs, 
  therefore, 
  must 
  be 
  given 
  with 
  certain 
  reservations. 
  

  

  The 
  testes 
  are 
  predominantly 
  ventral, 
  situated 
  mainly 
  below 
  the 
  

   level 
  of 
  the 
  intestinal 
  diverticula, 
  occasionally 
  extending 
  farther 
  

   dorsally 
  between 
  the 
  diverticula. 
  No 
  clearly 
  recognizable 
  testes 
  were 
  

   seen 
  behind 
  the 
  level 
  of 
  the 
  mouth; 
  they 
  may, 
  however, 
  appear 
  there 
  

  

  