﻿MONOPHLEBUS 
  STEBBINGI, 
  VAR. 
  OCTOCAUDATA. 
  47 
  

  

  ance 
  of 
  the 
  muscle 
  plate 
  in 
  Fig. 
  20. 
  This 
  transverse 
  series 
  (obtained 
  from 
  longitudinal 
  

   sections 
  of 
  the 
  insect) 
  also 
  show 
  well 
  the 
  groove 
  of 
  the 
  integument 
  in 
  which 
  the 
  

   spiracle 
  lies 
  and 
  the 
  relations 
  of 
  the 
  collar 
  chamber 
  with 
  the 
  external 
  aperture 
  . 
  

  

  3. 
  The 
  Structure 
  of 
  the 
  Abdominal 
  Spiracles. 
  

  

  There 
  are 
  seven 
  pairs 
  of 
  abdominal 
  spiracles 
  situated 
  on 
  the 
  dorsal 
  surface, 
  near 
  

   the 
  lateral 
  margins 
  of 
  the 
  insect 
  and 
  near 
  the 
  junctions 
  of 
  the 
  abdominal 
  segments, 
  

   but 
  there 
  is 
  no 
  spiracle 
  at 
  the 
  junction 
  of 
  the 
  metathorax 
  with 
  the 
  first 
  abdominal 
  

   segment. 
  

  

  The 
  external 
  opening 
  is 
  surrounded 
  by 
  a 
  chitinous 
  rim 
  ; 
  this 
  leads 
  into 
  a 
  chamber 
  

   (=collar 
  chamber 
  of 
  thoracic 
  spiracles) 
  the 
  walls 
  of 
  which 
  are 
  raised 
  into 
  a 
  prominent 
  

   spiral 
  thread 
  (Plate 
  IX, 
  figs. 
  22, 
  23). 
  Projecting 
  into 
  this 
  cavity 
  is 
  a 
  number 
  of 
  teeth, 
  

   — 
  eight 
  to 
  ten 
  — 
  which 
  are 
  united 
  at 
  their 
  bases 
  ; 
  their 
  free 
  pointed 
  ends 
  almost 
  approxi- 
  

   mate, 
  leaving 
  a 
  narrow 
  pore 
  — 
  the 
  opening 
  into 
  the 
  tracheal 
  tube 
  (Plate 
  IX, 
  figs. 
  22, 
  

   23, 
  26). 
  The 
  first 
  part 
  of 
  the 
  tracheal 
  tube 
  is 
  very 
  narrow 
  in 
  the 
  sections 
  examined, 
  

   and 
  is 
  surrounded 
  by 
  a 
  layer 
  of 
  spindle-shaped 
  cells 
  (G-), 
  which 
  suggest 
  a 
  muscular 
  

   function, 
  and 
  it 
  is 
  highly 
  probable 
  that 
  the 
  teeth 
  are 
  brought 
  together 
  and 
  the 
  narrow 
  

   lumen 
  occluded 
  by 
  the 
  relaxation 
  of 
  these 
  cells. 
  The 
  teeth 
  appear 
  to 
  bend 
  over 
  to 
  one 
  

   side 
  as 
  is 
  shown 
  in 
  transverse 
  and 
  longitudinal 
  sections 
  (Plate 
  IX, 
  figs. 
  22, 
  26). 
  

  

  Imperial 
  College 
  of 
  Science 
  and 
  Technology, 
  

  

  South 
  Kensington, 
  S.W. 
  

  

  