﻿THE 
  ANATOMY 
  OF 
  PtECILOCH.l^TUS, 
  CLAPAEEDE. 
  »/ 
  

  

  oose 
  coils 
  lying 
  immediately 
  in 
  front 
  of 
  the 
  head. 
  They 
  

   clearly 
  serve, 
  amongst 
  other 
  functions, 
  as 
  important 
  organs 
  

   of 
  respiration. 
  

  

  From 
  the 
  posterior 
  dorsal 
  region 
  of 
  the 
  head 
  three 
  long 
  

   tentacle-like 
  processes 
  arise, 
  a 
  long 
  median 
  process, 
  which 
  

   falls 
  back 
  on 
  the 
  dorsal 
  surface 
  of 
  the 
  body, 
  and 
  two 
  lateral 
  

   processes, 
  the 
  three 
  being 
  united 
  into 
  one 
  broad 
  base, 
  which 
  

   is 
  attached 
  to 
  the 
  head. 
  These 
  three 
  processes 
  constitute 
  the 
  

   nuchal 
  organ 
  (fig. 
  1 
  and 
  fig. 
  7, 
  nucli.), 
  the 
  very 
  great 
  develop- 
  

   ment 
  of 
  which 
  is 
  one 
  of 
  the 
  most 
  striking 
  features 
  of 
  the 
  

   genus 
  Pcecilocliffitus. 
  Occasionally 
  a 
  specimen 
  is 
  seen 
  in 
  

   which 
  one 
  or 
  other 
  of 
  the 
  three 
  processes 
  has 
  further 
  divided, 
  

   or 
  rather 
  given 
  off 
  a 
  well-developed 
  lateral 
  branch. 
  The 
  

   nuchal 
  organ 
  is 
  generally 
  of 
  a 
  brownish 
  colour 
  in 
  the 
  living 
  

   worm. 
  

  

  The 
  first 
  segment, 
  or 
  prostomium, 
  is 
  greatly 
  developed, 
  and 
  

   its 
  parapodia 
  and 
  chEeta3 
  are 
  directed 
  forwards. 
  Each 
  para- 
  

   podium 
  consists 
  of 
  a 
  neuropodium 
  and 
  a 
  notopodium 
  com- 
  

   pletely 
  united 
  together, 
  and 
  carries 
  a 
  ueuropodial 
  and 
  a 
  

   notopodial 
  cirrus, 
  the 
  former 
  being 
  large, 
  flask-shaped 
  and 
  

   directed 
  forwards, 
  whilst 
  the 
  latter 
  in 
  this 
  first 
  segment 
  is 
  

   small 
  and 
  rudimentary, 
  showing 
  merely 
  as 
  a 
  small 
  pro- 
  

   jection 
  on 
  the 
  dorsal 
  surface 
  of 
  the 
  parapodium 
  (PI. 
  8, 
  

   fig. 
  7). 
  

  

  There 
  are 
  two 
  bundles 
  of 
  simple, 
  long, 
  smooth 
  chtetJB, 
  

   which 
  extend 
  for 
  a 
  considerable 
  distance 
  in 
  front 
  of 
  the 
  head. 
  

   The 
  notopodial 
  cheette 
  are 
  about 
  twice 
  the 
  length 
  of 
  the 
  

   ueuropodial, 
  and 
  both 
  sets 
  curve 
  inwards, 
  the 
  longest 
  ones 
  

   often 
  crossing 
  their 
  fellows 
  of 
  the 
  opposite 
  side. 
  

  

  The 
  parapodia 
  and 
  their 
  cirri 
  are 
  covered 
  with 
  small 
  

   papillEe, 
  at 
  the 
  ends 
  of 
  which 
  are 
  the 
  external 
  openings 
  of 
  

   mucus 
  glands. 
  Between 
  the 
  ueuropodial 
  and 
  notopodial 
  

   cirrus 
  lies 
  a 
  well-developed 
  lateral 
  sense-organ, 
  similar 
  in 
  

   structure 
  to 
  those 
  found 
  on 
  all 
  the 
  anterior 
  segments 
  of 
  the 
  

   body. 
  These 
  organs 
  have 
  the 
  appearance 
  of 
  small, 
  pro- 
  

   jecting, 
  pear-shaped 
  lobes, 
  Avith 
  the 
  narrowest 
  portion 
  at 
  the 
  

   point 
  of 
  attachment 
  to 
  the 
  parapodium. 
  A 
  number 
  of 
  sensory 
  

  

  