﻿THE 
  ANATOMY 
  OF 
  P(ECILOCH.BT[JS, 
  OLAPARfeOE. 
  117 
  

  

  Ciliated 
  Groove 
  of 
  the 
  Alimentary 
  Canal. 
  — 
  Trans- 
  

   verse 
  sections 
  show 
  the 
  existence 
  of 
  a 
  deep, 
  longitudinal 
  

   ciliated 
  groove 
  running 
  along 
  the 
  mid-ventral 
  line 
  of 
  the 
  

   alimentary 
  canal 
  throughout 
  its 
  entire 
  length. 
  A 
  similar 
  

   groove 
  has 
  been 
  described 
  in 
  many 
  Polych^tes, 
  and 
  is 
  homo- 
  

   logous 
  with 
  the 
  secondary 
  intestine 
  (" 
  nebendarm 
  ") 
  of 
  the 
  

   Capitellids 
  (Eisig, 
  1887). 
  

  

  The 
  Epithelium 
  of 
  the 
  Alimentary 
  Canal. 
  — 
  The 
  

   epithelium 
  of 
  the 
  alimentary 
  canal^ 
  though 
  differing 
  much 
  in 
  

   appearance 
  in 
  its 
  different 
  parts^ 
  consists 
  essentially 
  of 
  cells 
  

   of 
  two 
  kinds, 
  (1) 
  columnar 
  epithelial 
  cells, 
  and 
  (2) 
  goblet- 
  

   shaped 
  gland-cells 
  lying 
  between 
  the 
  columnar 
  cells 
  and 
  

   opening 
  by 
  more 
  or 
  less 
  narrow 
  necks 
  into 
  the 
  lumen 
  of 
  the 
  

   canal. 
  

  

  The 
  columnar 
  epithelial 
  cells 
  of 
  the 
  oesophagus 
  (PI. 
  11, 
  fig. 
  

   44) 
  are 
  narrow 
  and 
  elongated, 
  with 
  large, 
  oval 
  nuclei, 
  the 
  

   long 
  axes 
  of 
  which 
  lie 
  parallel 
  to 
  the 
  long 
  axes 
  of 
  the 
  cells. 
  

   The 
  cells 
  themselves 
  are 
  strongly 
  ciliated 
  and 
  show 
  a 
  

   characteristic 
  structure, 
  similar 
  to 
  that 
  which 
  exists 
  in 
  other 
  

   ciliated 
  cells 
  of 
  the 
  worm 
  (compare 
  the 
  groove 
  of 
  the 
  nuchal 
  

   organ, 
  p. 
  114, 
  the 
  lateral 
  sense-organs, 
  p. 
  108, 
  and 
  the 
  epi- 
  

   thelium 
  of 
  the 
  genital 
  funnels, 
  p. 
  135). 
  The 
  appearance 
  pre- 
  

   sented 
  by 
  the 
  ciliated 
  borders 
  is 
  seen 
  in 
  fig. 
  44. 
  The 
  surface 
  

   of 
  each 
  cell 
  is 
  covered 
  by 
  a 
  thin 
  cuticle 
  (cu.) 
  continuous 
  with 
  

   the 
  cuticle 
  of 
  the 
  external 
  body 
  surface. 
  Immediately 
  within 
  

   this 
  cuticle 
  is 
  a 
  clear 
  space 
  through 
  which 
  the 
  inner 
  ends 
  of 
  

   the 
  cilia 
  are 
  seen 
  to 
  pass. 
  This 
  clear 
  space, 
  which 
  may 
  in 
  

   part 
  at 
  any 
  rate 
  be 
  due 
  to 
  contraction 
  of 
  the 
  contents 
  of 
  the 
  

   cells 
  during 
  the 
  preservation 
  of 
  the 
  tissue, 
  is 
  bounded 
  inter- 
  

   nally 
  by 
  a 
  layer 
  of 
  deeply 
  staining 
  short 
  rods 
  (.y. 
  v.), 
  which 
  

   appear 
  to 
  be 
  in 
  reality 
  slightly 
  thickened, 
  deeply 
  staining 
  

   portions 
  of 
  the 
  individual 
  cilia. 
  In 
  sections 
  these 
  rods 
  lie 
  in 
  

   a 
  straight 
  line 
  which 
  runs 
  parallel 
  to 
  the 
  cuticle. 
  Beyond 
  

   this 
  deeply 
  staining 
  layer 
  of 
  rods 
  the 
  ends 
  of 
  the 
  cilia 
  {I. 
  r.) 
  

   can 
  still 
  be 
  traced 
  for 
  some 
  little 
  distance 
  into 
  the 
  protoplasm 
  

   of 
  the 
  cell-body, 
  which 
  is 
  at 
  first 
  clear 
  excepting 
  for 
  tlie 
  

   striation 
  due 
  to 
  these 
  inner 
  ends 
  of 
  the 
  cilia, 
  and 
  subsequently 
  

  

  