﻿106 
  E. 
  J. 
  ALLEN. 
  

  

  developed 
  stomatogasfcric 
  nervous 
  system, 
  comprising 
  a 
  

   ganglion 
  and 
  a 
  large 
  bundle 
  of 
  nerve-fibres 
  on 
  the 
  pharynx, 
  

   is 
  found 
  in 
  Poecilochpetus, 
  but 
  my 
  preparations 
  have 
  not 
  

   sufl&ced 
  to 
  discover 
  the 
  complete 
  details 
  of 
  its 
  arrangement. 
  

  

  Lateral 
  Sense-organs. 
  

  

  The 
  position 
  and 
  external 
  appearance 
  of 
  the 
  lateral 
  sense- 
  

   organs 
  are 
  described 
  on 
  pp. 
  87 
  — 
  92 
  (figs. 
  1, 
  2, 
  7, 
  etc.). 
  In 
  

   segments 
  1 
  — 
  6, 
  as 
  well 
  as 
  in 
  the 
  segments 
  at 
  the 
  tail 
  end 
  of 
  

   the 
  body, 
  it 
  will 
  be 
  remembered 
  that 
  these 
  organs 
  have 
  the 
  

   form 
  of 
  pear-shaped 
  papillas 
  protruding 
  beyond 
  the 
  surface 
  

   of 
  the 
  parapodium 
  between 
  the 
  cirri, 
  whilst 
  in 
  the 
  remaining 
  

   segments 
  they 
  lie 
  in 
  the 
  parapodium 
  with 
  only 
  a 
  slightly 
  

   raised 
  rim 
  protruding 
  beyond 
  the 
  general 
  body 
  surface. 
  

  

  The 
  histological 
  structure 
  is 
  best 
  studied 
  in 
  detail 
  in 
  

   organs 
  of 
  the 
  latter 
  type, 
  as, 
  for 
  example, 
  in 
  those 
  at 
  about 
  

   segment 
  20, 
  and 
  the 
  most 
  instructive 
  general 
  view 
  is 
  seen 
  

   in 
  horizontal 
  sections 
  of 
  the 
  body. 
  Such 
  a 
  section 
  is 
  shown 
  

   in 
  fig. 
  34 
  (PI. 
  10), 
  which 
  passes 
  through 
  the 
  middle 
  of 
  a 
  lateral 
  

   organ. 
  Externally 
  the 
  organ 
  appears 
  as 
  a 
  cup-shaped 
  de- 
  

   pression 
  or 
  crater 
  surrounded 
  by 
  a 
  raised 
  circular 
  rim. 
  From 
  

   the 
  floor 
  of 
  the 
  depression 
  there 
  springs 
  a 
  mass 
  of 
  stiff 
  hairs, 
  

   which, 
  when 
  the 
  organ 
  is 
  not 
  much 
  contracted, 
  extend 
  far 
  

   beyond 
  the 
  raised 
  margin 
  of 
  the 
  rim. 
  

  

  The 
  external 
  rim 
  itself 
  is 
  composed 
  of 
  clear, 
  trans- 
  

   parent, 
  epithelial 
  cells, 
  often 
  showing 
  vacuoles 
  of 
  some 
  size 
  

   (PI. 
  10, 
  fig. 
  34, 
  ej). 
  r.) 
  These 
  cells, 
  as 
  well 
  as 
  the 
  face 
  of 
  the 
  

   depression 
  (haii'-bearing 
  area) 
  are 
  covered 
  externally 
  by 
  a 
  

   continuation 
  of 
  the 
  ordinary 
  body 
  cuticle 
  (en.), 
  which, 
  

   excepting 
  at 
  the 
  points 
  of 
  attachment 
  of 
  the 
  muscle-fibres 
  

   to 
  be 
  described 
  in 
  the 
  next 
  paragraph, 
  shows 
  no 
  marked 
  

   vai'iation 
  in 
  thickness 
  in 
  the 
  region 
  of 
  the 
  lateral 
  organs. 
  

  

  Internal 
  Muscular 
  System. 
  — 
  Immediately 
  within 
  the 
  

   epithelial 
  ridge 
  the 
  hair-bearing 
  area 
  is 
  surrounded 
  on 
  its 
  

   dorsal, 
  its 
  anterior 
  and 
  its 
  posterior 
  sides 
  by 
  bands 
  of 
  muscle- 
  

   fibre 
  [m.f.), 
  which 
  extend 
  from 
  the 
  cuticle 
  to 
  the 
  internal 
  

  

  