﻿300 
  W. 
  BLAXLAND 
  BENHAM. 
  

  

  studied 
  at 
  first 
  entire^ 
  stained 
  in 
  alum-cocliineal^ 
  and 
  mounted 
  

   in 
  Canada 
  balsam 
  ; 
  it 
  was 
  then 
  cut 
  into 
  a 
  seines 
  of 
  transverse 
  

   sections. 
  The 
  anterior 
  end 
  of 
  the 
  other 
  was 
  cut 
  longitudinally 
  ; 
  

   a 
  portion 
  from 
  the 
  middle 
  of 
  the 
  body 
  was 
  cut 
  transversely, 
  

   and 
  other 
  portions 
  of 
  the 
  worm 
  were 
  studied 
  in 
  glycerine. 
  

  

  The 
  prostomium, 
  as 
  usual 
  in 
  this 
  genus, 
  is 
  remarkably 
  

   long 
  and 
  narrow, 
  but 
  does 
  not 
  exhibit 
  any 
  annulation. 
  The 
  

   sensory 
  cells 
  form 
  a 
  thick 
  layer 
  over 
  its 
  whole 
  extent. 
  The 
  

   Segments 
  I 
  and 
  II 
  are 
  short, 
  and 
  the 
  subsequent 
  ones 
  become 
  

   progressively 
  larger 
  ; 
  the 
  body 
  is 
  much 
  dilated 
  in 
  the 
  region 
  

   occupied 
  by 
  the 
  sexual 
  products 
  (PI. 
  16, 
  fig. 
  1). 
  Each 
  segment 
  

   is 
  surrounded 
  by 
  a 
  ring 
  of 
  more 
  deeply 
  stained 
  nuclei 
  at 
  about 
  

   the 
  level 
  of 
  the 
  cha3t?e, 
  probably 
  a 
  ring 
  of 
  sensory 
  cells 
  ; 
  and 
  

   a 
  lateral 
  line 
  is 
  evident 
  in 
  transverse 
  section. 
  

  

  The 
  chsetae 
  are 
  four 
  in 
  number 
  in 
  each 
  segment 
  (fig. 
  15). 
  

   The 
  single 
  dorsal 
  chteta 
  is 
  only 
  about 
  one 
  third 
  to 
  one 
  half 
  

   the 
  length 
  of 
  the 
  single 
  ventral 
  one, 
  which 
  is 
  very 
  much 
  

   stouter 
  than 
  the 
  former 
  ; 
  both 
  are, 
  however, 
  alike 
  in 
  form 
  

   — 
  the 
  basal 
  region 
  is 
  straight, 
  the 
  freely 
  projecting 
  portion 
  

   is 
  curved 
  so 
  as 
  to 
  be 
  sickle 
  shaped 
  with 
  a 
  simple 
  point. 
  In 
  

   the 
  mid-body 
  the 
  dorsal 
  chteta 
  is 
  about 
  0'09 
  mm., 
  the 
  ventral 
  

   0*15 
  mm. 
  in 
  length. 
  The 
  dorsal 
  ch^tas 
  are 
  present 
  through- 
  

   out 
  the 
  worm. 
  

  

  The 
  clitellum 
  covers 
  Segments 
  XI 
  to 
  XIII 
  and 
  part 
  of 
  

   XIV 
  ; 
  it 
  surrounds 
  the 
  body, 
  but 
  is 
  better 
  developed 
  laterally 
  

   than 
  either 
  ventrally 
  or 
  dorsally, 
  indeed, 
  it 
  appears 
  in 
  trans- 
  

   verse 
  section 
  as 
  thinner 
  dorsally 
  than 
  elsewhere. 
  

  

  I 
  was 
  unable 
  to 
  detect 
  any 
  of 
  the 
  genital 
  pores 
  on 
  the 
  entire 
  

   worm 
  ; 
  but 
  from 
  a 
  study 
  of 
  sections 
  I 
  believe 
  that 
  the 
  two 
  

   pairs 
  of 
  male 
  pores 
  in 
  Segments 
  XI 
  and 
  XII 
  lie 
  just 
  in 
  front 
  

   of 
  the 
  ventral 
  chfetse. 
  There 
  is 
  a 
  single 
  pair 
  of 
  oviducal 
  

   pores 
  in 
  Segment 
  XIII 
  ; 
  each 
  ^Dore 
  is 
  external 
  to 
  the 
  line 
  of 
  

   ventral 
  cheetge, 
  and 
  lies 
  below 
  a 
  slightly 
  overhanging 
  pro- 
  

   jection 
  of 
  the 
  lateral 
  margin 
  of 
  the 
  ventral 
  surface. 
  In 
  the 
  

   possession 
  of 
  a 
  single 
  pair 
  of 
  female 
  gonads 
  and 
  ducts 
  this 
  

   species 
  differs 
  from 
  the 
  other 
  two 
  known 
  species, 
  H. 
  gor- 
  

   dioides, 
  and 
  H. 
  smithi; 
  hence 
  the 
  specific 
  name 
  hetero- 
  

  

  