﻿FRESH-WATER 
  TRICLADS 
  OF 
  ALASKA 
  — 
  KENK 
  

  

  171 
  

  

  coronata. 
  Hyman 
  (1931, 
  p. 
  126) 
  states 
  that 
  in 
  P. 
  coronata 
  the 
  

   curved 
  band 
  of 
  eyes 
  narrows 
  as 
  it 
  crosses 
  the 
  base 
  of 
  the 
  auricles; 
  

   no 
  such 
  narrowing 
  has 
  been 
  seen 
  in 
  P. 
  borealis. 
  These 
  differences 
  

   are, 
  however, 
  insignificant 
  and 
  do 
  not 
  permit 
  a 
  clear 
  separation 
  of 
  

   the 
  two 
  forms. 
  The 
  same 
  may 
  be 
  said 
  of 
  other 
  species 
  of 
  the 
  genus, 
  

   which 
  likewise 
  could 
  be 
  confused 
  with 
  the 
  American 
  forms 
  in 
  life: 
  

   the 
  Japanese 
  species, 
  P. 
  auriculata 
  and 
  P. 
  karafto; 
  and 
  P. 
  schmidti 
  

   occurring 
  both 
  in 
  Kamchatka 
  and 
  in 
  Japan. 
  These 
  forms 
  differ 
  

   from 
  each 
  other 
  more 
  clearly 
  in 
  their 
  anatomical 
  characters. 
  

  

  bd 
  ode 
  

  

  Figure 
  22. 
  — 
  Polycelis 
  borealis, 
  diagram 
  of 
  the 
  copulatory 
  organs 
  in 
  longitudinal 
  section, 
  

   X 
  70. 
  a, 
  atrium; 
  b, 
  bursa; 
  bd, 
  bursa 
  stalk; 
  de, 
  ejaculatory 
  duct; 
  o, 
  mouth; 
  ode, 
  common 
  

   oviduct; 
  pg, 
  genital 
  pore; 
  vd, 
  vas 
  deferens; 
  vs, 
  seminal 
  vesicle. 
  

  

  To 
  gain 
  a 
  better 
  insight 
  into 
  the 
  systematic 
  relations 
  of 
  Poly- 
  

   celis 
  borealis 
  to 
  other 
  species 
  of 
  the 
  same 
  genus, 
  it 
  is 
  necessary 
  to 
  review 
  

   the 
  present 
  state 
  of 
  the 
  systematics 
  of 
  the 
  genus. 
  The 
  genus 
  Poly- 
  

   celis 
  has 
  a 
  muscular 
  pattern 
  of 
  the 
  pharynx 
  typical 
  of 
  the 
  family 
  

   Planariidae; 
  the 
  oviducts 
  unite, 
  without 
  embracing 
  the 
  bursa 
  stalk, 
  

   to 
  form 
  an 
  unpaired 
  terminal 
  oviduct; 
  the 
  testes 
  are 
  situated 
  in 
  the 
  

   anterior 
  part 
  of 
  the 
  body 
  only; 
  the 
  male 
  atrium 
  is 
  not 
  surrounded 
  

   by 
  radial 
  muscle 
  plates; 
  and 
  the 
  eyes 
  are 
  numerous. 
  The 
  genus 
  

   thus 
  defined 
  (Kenk, 
  1930) 
  has 
  today 
  about 
  twenty 
  species. 
  It 
  may 
  

   be 
  subdivided 
  into 
  subgenera 
  on 
  the 
  basis 
  of 
  structural 
  characters 
  

   of 
  the 
  copulatory 
  apparatus. 
  

  

  Subgenus 
  Polycelis, 
  lacking 
  adenodactyls 
  and 
  lacking 
  an 
  excessive 
  

   development 
  of 
  the 
  muscle 
  coat 
  of 
  the 
  male 
  atrium. 
  This 
  subgenus 
  

   includes 
  Sorocelides 
  Sabussowa 
  (1929, 
  p. 
  521) 
  and 
  Polycelidia 
  Zabu- 
  

   sova 
  (1936, 
  p. 
  152), 
  both 
  described 
  as 
  distinct 
  genera. 
  The 
  subgenus 
  

   comprises 
  the 
  following 
  species: 
  

  

  238538—53 
  

  

  