﻿104 
  E. 
  J. 
  ALLEN. 
  

  

  ganglion 
  receives 
  the 
  fibres 
  of 
  the 
  palp-ganglion 
  nerve 
  (the 
  

   origin 
  of 
  which 
  in 
  the 
  brain 
  has 
  already 
  been 
  described), 
  and 
  

   gives 
  off 
  a 
  bundle 
  of 
  nerve-fibres, 
  which 
  immediately 
  enters 
  

   the 
  palp. 
  

  

  The 
  Nuchal 
  Ganglion, 
  — 
  The 
  uuchal 
  ganglion 
  lies 
  in 
  the 
  

   base 
  of 
  the 
  nuchal 
  organ, 
  and 
  consists 
  of 
  a 
  considerable 
  mass 
  of 
  

   nervous 
  felt-work 
  surrounded 
  by 
  a 
  number 
  of 
  ganglion-cells, 
  

   some 
  of 
  them 
  of 
  large 
  size. 
  Bundles 
  of 
  nerve-fibres 
  pass 
  from 
  

   it 
  into 
  the 
  different 
  branches 
  of 
  the 
  organ, 
  and 
  these 
  doubt- 
  

   less 
  supply 
  the 
  external 
  ciliated 
  grooves 
  which 
  run 
  along 
  

   those 
  branches 
  (cf. 
  p. 
  112), 
  though 
  individual 
  fibres 
  have 
  

   not 
  actually 
  been 
  traced 
  so 
  far. 
  

  

  The 
  Relation 
  of 
  the 
  Different 
  Parts 
  of 
  the 
  Brain 
  

   to 
  one 
  another. 
  — 
  The 
  arrangement 
  of 
  the 
  brain 
  and 
  the 
  

   ganglia 
  connected 
  with 
  it 
  in 
  Poecilochffitus 
  is 
  of 
  some 
  theo- 
  

   retical 
  interest 
  when 
  considered 
  in 
  connection 
  with 
  that 
  of 
  

   other 
  Polychajtes. 
  Our 
  recent 
  kuowledge 
  of 
  the 
  structure 
  of 
  

   the 
  Polycheete 
  enchaphalon 
  is 
  largely 
  based 
  on 
  the 
  careful 
  work 
  

   of 
  Racovitza 
  (1896). 
  This 
  author 
  distinguishes 
  three 
  regions, 
  

   to 
  which 
  he 
  gives 
  equal 
  morphological 
  importance 
  — 
  the 
  fore- 
  

   brain 
  (Cerveau 
  ante 
  rieur), 
  with 
  which 
  the 
  palp-ganglia 
  are 
  

   connected; 
  tlie 
  mid-brain 
  (Cerveau 
  moyen) 
  with 
  the 
  anten- 
  

   nary 
  and 
  optic 
  ganglia; 
  and 
  the 
  hind 
  brain 
  (Cerveau 
  poste- 
  

   rieur) 
  with 
  the 
  nuchal 
  ganglia. 
  The 
  relations 
  of 
  the 
  parts 
  in 
  

   Poecilochfetus 
  are 
  noteworthy 
  ia 
  that 
  the 
  palp-ganglia 
  and 
  

   the 
  nuchal 
  ganglion 
  are 
  not 
  fused 
  in 
  the 
  mass 
  of 
  the 
  brain, 
  as 
  in 
  

   the 
  forms 
  described 
  by 
  Racovitza, 
  but 
  are 
  separated 
  distinctly 
  

   from 
  it. 
  The 
  eyes 
  being 
  simple, 
  there 
  is 
  no 
  development 
  of 
  

   optic 
  ganglia, 
  and 
  the 
  antennary 
  ganglia 
  are 
  also 
  not 
  obvious. 
  

   With 
  regard 
  to 
  the 
  divisions 
  of 
  the 
  brain 
  itself, 
  the 
  facts 
  

   point 
  to 
  the 
  presence 
  of 
  the 
  first 
  two 
  at 
  any 
  rate 
  of 
  Raco- 
  

   vitza's 
  three 
  regions, 
  though 
  the 
  matter 
  is 
  by 
  no 
  means 
  clear. 
  

   The 
  anterior 
  ganglion-cells 
  (Text-fig. 
  1, 
  ant. 
  gang, 
  celh), 
  

   with 
  their 
  bundle 
  of 
  fibres, 
  which, 
  as 
  has 
  been 
  stated, 
  very 
  

   possibly 
  form 
  the 
  first 
  I'oot 
  of 
  the 
  palp-ganglion 
  nerve, 
  would 
  

   represent 
  the 
  fore-brain 
  of 
  Racovitza, 
  whilst 
  the 
  fact 
  that 
  the 
  

   nerves 
  to 
  the 
  tentacle 
  {n. 
  t.) 
  and 
  the 
  oesophageal 
  commissures 
  

  

  