﻿THE 
  ANATOMY 
  OP 
  FCECILOCHJLTUS, 
  OLAPABEDE. 
  lOl 
  

  

  Cha3ta3. 
  

  

  An 
  account 
  has 
  already 
  been 
  given, 
  in 
  describing 
  the 
  ex- 
  

   ternal 
  features, 
  of 
  the 
  different 
  types 
  oE 
  bristles 
  which 
  Poecilo 
  - 
  

   chtet 
  us 
  possesses 
  (see 
  PL 
  9, 
  figs. 
  13 
  — 
  19). 
  The 
  shafts 
  of 
  these 
  

   bristles 
  almost 
  all 
  show 
  longitudinal 
  striation, 
  together 
  with 
  

   transverse 
  markings 
  at 
  irregular 
  intervals. 
  The 
  longitudinal 
  

   striations 
  are 
  shown 
  in 
  sections 
  to 
  be 
  due 
  to 
  the 
  fact 
  that 
  the 
  

   bristle 
  is 
  built 
  up 
  of 
  a 
  large 
  number 
  of 
  longitudinal 
  tubes 
  

   lying 
  side 
  by 
  side. 
  This 
  is 
  especially 
  marked 
  in 
  the 
  stout 
  

   hooks 
  of 
  the 
  neuropodium, 
  which 
  occur 
  in 
  segments 
  2 
  and 
  3, 
  

   and 
  in 
  the 
  hooks 
  of 
  the 
  notopodium 
  in 
  the 
  terminal 
  segments. 
  

   All 
  chsetae 
  with 
  stout 
  shafts 
  also 
  show 
  the 
  structure 
  well. 
  

  

  This 
  type 
  of 
  minute 
  structure 
  in 
  the 
  bristles 
  of 
  Chtetopods 
  

   has 
  recently 
  been 
  described 
  in 
  detail 
  by 
  Schepotieff 
  (1903), 
  

   to 
  whose 
  paper 
  reference 
  should 
  be 
  made 
  for 
  further 
  details. 
  

  

  Nervous 
  System. 
  

  

  Brain. 
  — 
  Practically 
  the 
  whole 
  of 
  the 
  head 
  of 
  the 
  worm 
  is 
  

   occupied 
  by 
  the 
  substance 
  of 
  the 
  brain. 
  This 
  substance 
  con- 
  

   sists 
  of 
  a 
  ventral^ 
  mass 
  of 
  nervous 
  felt-work 
  (punctated 
  sub- 
  

   stance) 
  covered 
  externally 
  by 
  a 
  mass 
  of 
  ganglion-cells. 
  

  

  The 
  arrangement 
  of 
  the 
  parts 
  can 
  be 
  best 
  explained 
  by 
  

   reference 
  to 
  the 
  diagrammatic 
  figure 
  of 
  a 
  section 
  of 
  the 
  brain 
  

   given 
  in 
  the 
  text 
  (Fig. 
  1). 
  

  

  This 
  figure 
  represents 
  a 
  thick 
  sagittal 
  (longitudinal-vertical) 
  

   section 
  through 
  the 
  brain 
  cut 
  a 
  little 
  on 
  one 
  side 
  of 
  the 
  middle 
  

   line, 
  and 
  has 
  been 
  constructed 
  from 
  an 
  examination 
  of 
  several 
  

   series 
  of 
  thin 
  sections. 
  The 
  large 
  circumoesophageal 
  commis- 
  

   sures, 
  which 
  put 
  the 
  brain 
  in 
  communication 
  with 
  the 
  ventral 
  

   nerve-cord 
  of 
  the 
  worm, 
  can 
  be 
  traced 
  from 
  the 
  particular 
  mass 
  

   of 
  punctated 
  substance 
  which 
  occupies 
  the 
  centre 
  of 
  the 
  brain 
  

  

  * 
  In 
  the 
  description 
  of 
  the 
  brain 
  the 
  terms 
  anterior, 
  posterior, 
  dorsal 
  and 
  

   ventral 
  are 
  used 
  on 
  the 
  assumption 
  that 
  the 
  worm 
  has 
  the 
  proboscis 
  slightly 
  

   everted 
  as 
  in 
  the 
  sagittal 
  section 
  fig. 
  42 
  (PI. 
  11). 
  In 
  the 
  position 
  of 
  repose, 
  

   what 
  is 
  here 
  called 
  the 
  anterior 
  surface, 
  becomes 
  more 
  ventral 
  in 
  position. 
  

  

  