﻿120 
  E. 
  J. 
  ALLEN. 
  

  

  numerous 
  than 
  those 
  in 
  cells 
  of 
  the 
  previous 
  type 
  and 
  stain 
  

   blue 
  instead 
  of 
  red 
  (fig. 
  44^ 
  gl. 
  2). 
  

  

  (3) 
  Cells 
  still 
  of 
  the 
  same 
  general 
  shape, 
  but 
  less 
  swollen, 
  

   without 
  granules, 
  but 
  filled 
  with 
  a 
  homogeneous 
  substance 
  

   staining 
  faintly 
  blue 
  and 
  showing 
  at 
  most 
  slight 
  indications 
  

   of 
  a 
  network 
  such 
  as 
  is 
  usually 
  produced 
  by 
  the 
  action 
  of 
  

   preserving 
  fluids 
  ; 
  the 
  nuclei 
  of 
  these 
  cells 
  stain 
  more 
  deeply 
  

   and 
  more 
  diffusely 
  than 
  those 
  of 
  the 
  previous 
  types, 
  their 
  

   ground 
  substance 
  taking 
  on 
  a 
  faint 
  blue 
  tint, 
  whilst 
  the 
  

   chromatin 
  is 
  red 
  or 
  purple 
  (fig. 
  44, 
  gl. 
  3). 
  

  

  Cells 
  of 
  the 
  first 
  and 
  second 
  kinds 
  are 
  clearly 
  actively 
  

   secreting 
  cells, 
  whilst 
  those 
  of 
  the 
  third 
  kind 
  seem 
  to 
  be 
  cells 
  

   of 
  the 
  second 
  which 
  have 
  completely 
  discharged 
  their 
  secre- 
  

   tion 
  and 
  are 
  in 
  a 
  resting 
  condition, 
  in 
  all 
  probability 
  waiting 
  

   to 
  commence 
  the 
  secretory 
  process 
  upon 
  suitable 
  stimulation. 
  

   In 
  some 
  specimens 
  nearly 
  all 
  the 
  gland-cells 
  in 
  the 
  oeso- 
  

   phagus 
  are 
  iu 
  the 
  condition 
  last 
  described. 
  

  

  As 
  will 
  be 
  seen 
  by 
  comparing 
  the 
  two 
  sets 
  of 
  figures 
  and 
  

   the 
  two 
  descriptions, 
  the 
  gland-cells 
  of 
  the 
  oesophagus 
  show 
  

   many 
  points 
  of 
  resemblance 
  with 
  the 
  gland-cells 
  of 
  the 
  skin 
  

   and 
  of 
  the 
  parapodial 
  cirri. 
  

  

  The 
  structure 
  of 
  the 
  epithelium 
  of 
  the 
  pharynx 
  and 
  of 
  the 
  

   anterior 
  portion 
  of 
  the 
  intestine 
  is 
  essentially 
  the 
  same 
  as 
  that 
  

   which 
  has 
  been 
  described 
  for 
  the 
  oesophagus 
  ; 
  the 
  cells, 
  how- 
  

   ever, 
  become 
  gradually 
  less 
  elongated 
  in 
  shape, 
  and 
  the 
  

   number 
  of 
  gland-cells 
  diminishes. 
  

  

  At 
  about 
  segment 
  16 
  or 
  17 
  the 
  type 
  of 
  intestinal 
  epithelium 
  

   which 
  persists 
  through 
  the 
  greater 
  part 
  of 
  the 
  body 
  of 
  the 
  

   worm 
  is 
  established. 
  This 
  epithelium 
  is 
  found 
  in 
  two 
  

   markedly 
  different 
  conditions, 
  which 
  appear 
  to 
  depend 
  upon 
  

   whether 
  the 
  intestine 
  is 
  filled 
  with 
  food 
  and 
  digestion 
  is 
  

   actively 
  going 
  on, 
  or 
  whether 
  food 
  is 
  absent 
  from 
  it. 
  These 
  

   two 
  conditions 
  are 
  illustrated 
  in 
  figs. 
  45 
  and 
  46 
  (PI. 
  11). 
  

  

  Fig. 
  45 
  shows 
  the 
  state 
  of 
  things 
  which 
  is 
  found 
  when 
  food 
  

   is 
  present 
  and 
  digestion 
  is 
  actively 
  proceeding. 
  The 
  epithelial 
  

   cells 
  {ep.) 
  are 
  large 
  and 
  swollen, 
  whilst 
  the 
  gland-cells 
  have 
  

   shrivelled 
  till 
  little 
  more 
  than 
  the 
  nucleus 
  is 
  visible 
  [gl.]. 
  

  

  