﻿THE 
  ANATOMY 
  OF 
  rcEClLOCHJlTUS, 
  CLAPAKEDE. 
  Ill 
  

  

  the 
  organs 
  of 
  PoecilochaetuSj 
  whilst 
  the 
  deeply 
  staiuing 
  

   layer 
  of 
  short 
  rods 
  either 
  does 
  not 
  exist 
  in 
  the 
  Capitellids 
  or 
  

   was 
  not 
  rendered 
  evident 
  by 
  the 
  methods 
  employed. 
  The 
  

   spindles 
  of 
  Eisig 
  I 
  am 
  inclined 
  to 
  regard 
  as 
  the 
  nuclei 
  of 
  the 
  

   hair-bearing 
  cells, 
  being 
  led 
  to 
  this 
  view 
  by 
  a 
  comparison 
  of 
  

   the 
  structure 
  of 
  the 
  hair-bearing 
  cells 
  with 
  the 
  ciliated 
  cells 
  of 
  

   the 
  nuchal 
  grooves 
  and 
  of 
  the 
  oesophagus 
  inPcecilochaetus. 
  

   On 
  the 
  other 
  hand, 
  they 
  may 
  represent 
  bipolar 
  ganglion-cells. 
  

  

  Ashworth 
  (1902) 
  has 
  recently 
  written 
  on 
  the 
  structure 
  of 
  the 
  

   lateral 
  sense-organs 
  in 
  Scalibregma 
  inflatum. 
  He 
  de- 
  

   scribes 
  and 
  figures 
  the 
  sensory 
  hairs, 
  the 
  layer 
  of 
  short, 
  deeply 
  

   staiuing 
  rods, 
  and 
  tbe 
  long 
  rods, 
  all 
  of 
  which 
  have 
  apparently 
  

   the 
  same 
  relations 
  as 
  in 
  Poecilochaitus. 
  Ashworth, 
  how- 
  

   ever, 
  interprets 
  the 
  long 
  rods 
  as 
  hair-bearing 
  cells 
  and 
  the 
  

   deeply 
  staining 
  short 
  rods 
  as 
  their 
  nuclei. 
  With 
  this 
  inter- 
  

   pretation 
  1 
  am 
  unable 
  to 
  agree, 
  both 
  from 
  the 
  appearance 
  of 
  

   the 
  structures 
  themselves 
  in 
  my 
  preparations 
  as 
  well 
  as 
  from 
  

   a 
  comparison 
  with 
  the 
  known 
  structure 
  of 
  ciliated 
  cells 
  (cf. 
  

   p. 
  118). 
  

  

  Ashworth 
  also 
  describes 
  and 
  figures 
  large 
  unipolar 
  and 
  

   bipolar 
  ganglion-cells 
  similar 
  to 
  those 
  found 
  in 
  Poecilo- 
  

   chsetus, 
  and 
  states 
  that 
  the 
  processes 
  of 
  these 
  cells 
  can 
  be 
  

   traced 
  into 
  continuity 
  with 
  the 
  internal 
  ends 
  of 
  the 
  rods 
  which 
  

   carry 
  the 
  sense-hairs. 
  I 
  have 
  been 
  unable 
  to 
  make 
  out 
  with 
  

   certainty 
  such 
  a 
  connection 
  in 
  Pcecilocheetus, 
  though 
  the 
  

   appearances 
  presented 
  are 
  in 
  no 
  way 
  opposed 
  to 
  its 
  ex- 
  

   istence. 
  

  

  Further 
  studies 
  on 
  the 
  lateral 
  sense-organs 
  in 
  the 
  different 
  

   groups 
  of 
  Polycha3tes, 
  made 
  with 
  the 
  aid 
  of 
  more 
  special 
  

   methods 
  for 
  determining 
  the 
  course 
  of 
  the 
  nervous 
  fibres, 
  are 
  

   necessary 
  before 
  their 
  structure 
  can 
  be 
  fully 
  understood. 
  

  

  Nuchal 
  Organ. 
  

  

  One 
  of 
  the 
  most 
  characteristic 
  features 
  of 
  the 
  genus 
  Poeci- 
  

  

  lochgetus 
  is 
  the 
  great 
  development 
  of 
  the 
  nuchal 
  organ, 
  

  

  which, 
  as 
  already 
  stated, 
  consists 
  of 
  a 
  broad, 
  basal 
  portion 
  

  

  springing 
  from 
  the 
  dorsal 
  surface 
  of 
  the 
  posterior 
  end 
  of 
  the 
  

  

  