﻿THE 
  ANATOMY 
  OF 
  PCEOILOOHJUTUS, 
  CLAPArIiDE. 
  93 
  

  

  again 
  tlie 
  form 
  of 
  pear-shaped 
  papillge 
  protruding 
  from 
  the 
  

   surfaces 
  of 
  the 
  parapodia 
  between 
  the 
  cirri. 
  

  

  The 
  pygidium 
  is 
  well 
  developed 
  ; 
  the 
  anus 
  is 
  somewhat 
  

   dorsal, 
  and 
  is 
  surrounded 
  by 
  five 
  large 
  lobes 
  (PI. 
  8, 
  fig. 
  6). 
  

   There 
  are 
  two 
  pairs 
  of 
  anal 
  cirri, 
  both 
  situated 
  below 
  the 
  

   anus, 
  the 
  more 
  dorsal 
  pair 
  being 
  long 
  and 
  slender, 
  the 
  more 
  

   ventral 
  pair 
  short. 
  

  

  The 
  anus 
  and 
  the 
  terminal 
  portion 
  of 
  the 
  intestine 
  are 
  

   strongly 
  ciliated, 
  and 
  all 
  the 
  cirri 
  in 
  the 
  hindermost 
  region 
  of 
  

   the 
  body, 
  as 
  well 
  as 
  the 
  dorsal 
  and 
  ventral 
  surfaces 
  of 
  the 
  

   body 
  itself, 
  are 
  very 
  richly 
  provided 
  with 
  papillae, 
  at 
  the 
  

   extremities 
  of 
  which 
  lie 
  the 
  external 
  openings 
  of 
  epithelial 
  

   glands. 
  

  

  No 
  description 
  of 
  the 
  general 
  aspect 
  of 
  the 
  living 
  Poecilo- 
  

   chfetus 
  is 
  complete 
  without 
  reference 
  to 
  the 
  remarkable 
  

   system 
  of 
  blood-vessels, 
  which 
  is 
  visible 
  through 
  the 
  tran- 
  

   parent 
  body-wall 
  (Fig. 
  1). 
  A 
  detailed 
  nccouut 
  of 
  tliis 
  vascular 
  

   system 
  will 
  be 
  found 
  in 
  the 
  special 
  section 
  on 
  p. 
  126. 
  

  

  Internal 
  Anatomy 
  and 
  Histology. 
  

   ♦ 
  Epithelium 
  and 
  Cuticle. 
  

  

  The 
  character 
  of 
  the 
  epithelium 
  differs 
  in 
  different 
  parts 
  of 
  

   the 
  body. 
  The 
  cells 
  composing 
  it 
  may 
  be 
  either 
  almost 
  

   cubical, 
  with 
  spherical 
  nuclei 
  (PI. 
  9, 
  fig. 
  20), 
  or 
  they 
  may 
  

   be 
  elongated 
  in 
  a 
  direction 
  either 
  perpendicular 
  (PI. 
  9, 
  

   fig. 
  21) 
  or 
  parallel 
  to 
  the 
  body 
  surface 
  (PI. 
  10, 
  fig. 
  23). 
  The 
  

   elongated 
  cells 
  have 
  oval 
  nuclei, 
  the 
  long 
  axes 
  of 
  which 
  are 
  

   parallel 
  to 
  the 
  long 
  axes 
  of 
  the 
  cells. 
  

  

  Over 
  the 
  greater 
  part 
  of 
  the 
  body 
  the 
  epithelial 
  cells 
  are 
  

   arranged 
  in 
  a 
  single 
  layer, 
  but 
  in 
  isolated 
  places, 
  more 
  

   especially 
  on 
  the 
  ventro-lateral 
  surfaces 
  to 
  be 
  presently 
  

   described, 
  two 
  layers 
  can 
  be 
  recognised. 
  The 
  cuticle, 
  which 
  

   lies 
  external 
  to 
  the 
  epithelial 
  cells, 
  varies 
  in 
  thickness 
  in 
  

   different 
  parts 
  of 
  the 
  body. 
  

  

  Cells 
  nearly 
  cubical 
  in 
  shape 
  are 
  found 
  on 
  the 
  dorsal 
  

  

  