﻿NOTEg 
  OK 
  RHABDOPLEURA 
  NORMANF, 
  AT.LMAN. 
  2o 
  

  

  the 
  insertion 
  of 
  the 
  stalk 
  is 
  indicated 
  by 
  a 
  thin 
  crescentic 
  

   plate 
  of 
  longitudinal 
  muscle-fibres, 
  which 
  seem 
  to 
  form 
  part 
  

   of 
  the 
  somatic 
  mesoderm 
  of 
  the 
  body 
  on 
  the 
  ventral 
  surface. 
  

   Tliey 
  are 
  first 
  recognisable 
  some 
  little 
  distance 
  above 
  

   (anterior 
  to) 
  the 
  bend 
  of 
  the 
  alimentary 
  canal. 
  At 
  the 
  level 
  

   of 
  the 
  intestinal 
  flexure 
  the 
  muscle-plate 
  has 
  become 
  some- 
  

   what 
  thicker 
  (fig. 
  1). 
  

  

  When 
  clear 
  of 
  the 
  body 
  of 
  the 
  polyp, 
  the 
  soft 
  pai't 
  of 
  the 
  

   stalk 
  (^^ 
  gymnocaulus" 
  of 
  Lankester) 
  shows 
  the 
  relations 
  re- 
  

   presented 
  diagram 
  maticall}' 
  in 
  fig. 
  2. 
  It 
  is 
  presumably 
  

   covered 
  entirely 
  by 
  ectoderm 
  ; 
  this 
  ectoderm 
  is 
  certainly 
  

   thick 
  and 
  glandular 
  on 
  the 
  upper 
  side, 
  that 
  turned 
  towards 
  

   the 
  polyp. 
  Beneath 
  this 
  lies 
  the 
  longitudinal 
  muscle 
  as 
  two 
  

   J-shaped 
  bands 
  separated 
  from 
  one 
  another 
  by 
  a 
  septum, 
  

   which 
  bisects 
  the 
  cavity 
  of 
  the 
  stalk. 
  At 
  the 
  ventral 
  border 
  

   of 
  this 
  septum 
  the 
  ectoderm 
  is 
  thickened 
  into 
  a 
  triangle, 
  the 
  

   cells 
  of 
  which 
  are 
  not 
  pigmented, 
  as 
  is 
  the 
  rest 
  of 
  the 
  ecto- 
  

   derm, 
  and 
  stain 
  very 
  faintly 
  ; 
  they 
  have 
  very 
  much 
  the 
  

   appearance 
  of 
  a 
  superficial 
  nerve 
  (figs. 
  2, 
  3, 
  a). 
  Abutting 
  on 
  

   this 
  triangle 
  a 
  fine 
  canal 
  is 
  excavated 
  in 
  the 
  substance 
  of 
  the 
  

   mesentery, 
  recognisable 
  in 
  many 
  sections 
  and 
  several 
  speci- 
  

   mens, 
  but 
  not 
  in 
  nil 
  ; 
  it 
  may 
  perhaps 
  be 
  an 
  artificial 
  

   structure 
  (fig. 
  2, 
  h). 
  In 
  the 
  central 
  part 
  of 
  the 
  stalk 
  another 
  

   cavity 
  is 
  always 
  visible, 
  generally 
  completely 
  filled 
  with 
  a 
  

   granular 
  mass, 
  but 
  in 
  the 
  section 
  figured 
  this 
  mass 
  had 
  

   shrunk 
  away 
  from 
  the 
  walls, 
  which 
  are 
  thus 
  rendered 
  more 
  

   conspicuous 
  (figs. 
  2, 
  3, 
  end?). 
  

  

  At 
  the 
  junction 
  of 
  the 
  soft 
  stalk 
  with 
  the 
  body 
  the 
  rela- 
  

   tions 
  are 
  extremely 
  difficult 
  to 
  determine, 
  owing 
  to 
  the 
  

   obliquity 
  of 
  the 
  structures 
  concerned 
  and 
  to 
  a 
  rotation 
  of 
  the 
  

   stalk. 
  The 
  coelom 
  is 
  comparatively 
  broad 
  at 
  the 
  point 
  of 
  

   insertion, 
  and 
  I 
  believe 
  that 
  I 
  can 
  trace 
  the 
  paired 
  cavities 
  of 
  

   the 
  stalk 
  into 
  the 
  coelom, 
  and 
  the 
  central 
  cavity 
  of 
  the 
  

   mesentery 
  into 
  continuity 
  with 
  the 
  endoderm. 
  In 
  palliation 
  

   of 
  this 
  uncertainty, 
  I 
  have 
  drawn 
  the 
  outline 
  of 
  a 
  human 
  red 
  

   blood-corpuscle 
  on 
  the 
  same 
  scale 
  (fig. 
  2, 
  r. 
  c), 
  from 
  which 
  it 
  

   may 
  be 
  gathered 
  readily 
  that 
  the 
  difficulty 
  of 
  study 
  of 
  such 
  

  

  VOL. 
  48, 
  PART 
  1. 
  NEW 
  SERIES. 
  3 
  

  

  