﻿ROBT. 
  E. 
  SAVAGE 
  — 
  THE 
  RESPIRATORY 
  SYSTEM 
  OF 
  

  

  2. 
  The 
  Structure 
  of 
  the 
  Thoracic 
  Spiracles. 
  

  

  The 
  structure 
  of 
  the 
  thoracic 
  spiracles 
  was 
  studied 
  (1) 
  by 
  means 
  of 
  whole 
  mounts 
  

   of 
  the 
  spiracles, 
  obtained 
  by 
  dissecting 
  them 
  out 
  and 
  then 
  boiling 
  in 
  10 
  per 
  cent. 
  

   KOH 
  solution 
  ; 
  and 
  (2) 
  by 
  longitudinal 
  and 
  transverse 
  sections 
  of 
  the 
  spiracles 
  (Plates 
  

   VII 
  and 
  VIII). 
  Horizontal 
  sections 
  were 
  not 
  procured 
  because 
  of 
  the 
  difficulty 
  of 
  

   obtaining 
  them 
  really 
  horizontal. 
  Two 
  fixatives 
  were 
  used 
  : 
  — 
  (1) 
  Corrosive 
  acetic 
  

   alcohol, 
  and 
  (2) 
  boiling 
  picro-sulphuric 
  (Kleinenberg's 
  formula). 
  The 
  best 
  results 
  were 
  

   obtained 
  by 
  using 
  the 
  former. 
  Embedding 
  for 
  seven 
  hours 
  in 
  paraffin 
  wax 
  of 
  melting 
  

   point 
  58° 
  C. 
  was 
  found 
  to 
  be 
  very 
  satisfactory.* 
  

  

  The 
  thoracic 
  spiracles 
  are 
  situated 
  on 
  the 
  ventral 
  surface 
  of 
  the 
  insect 
  near 
  the 
  

   lateral 
  margin, 
  the 
  mesothoracic 
  just 
  behind 
  the 
  junction 
  of 
  the 
  pro- 
  and 
  meso- 
  

   sternum, 
  and 
  the 
  metathoracic 
  just 
  posterior 
  to 
  the 
  junction 
  of 
  the 
  meso- 
  and 
  meta- 
  

   .sternum. 
  The 
  aperture 
  is 
  laterally 
  placed, 
  whilst 
  the 
  " 
  muscle 
  plate 
  " 
  (see 
  below) 
  

   is 
  ventral 
  and 
  somewhat 
  anteriorly 
  directed 
  (Plate 
  V, 
  fig. 
  2). 
  In 
  the 
  adult 
  insect 
  the 
  

   spiracles 
  are 
  in 
  grooves 
  of 
  the 
  integument 
  (Plate 
  VI, 
  fig. 
  4). 
  

  

  The 
  aperture 
  of 
  the 
  spiracle 
  is 
  surrounded 
  by 
  a 
  chitinous 
  rim 
  (Plate 
  VI, 
  figs. 
  3, 
  4-C,), 
  

   which 
  is 
  continuous 
  ventrally 
  with 
  what 
  will 
  be 
  called 
  the 
  muscle-plate 
  (C 
  2 
  ), 
  a 
  very 
  

   strong 
  and 
  thick 
  chitinous 
  structure, 
  which, 
  as 
  will 
  be 
  seen 
  below, 
  serves 
  for 
  the 
  attach- 
  

   ment 
  of 
  the 
  muscles 
  in 
  connection 
  with 
  the 
  closing 
  apparatus. 
  The 
  aperture 
  leads 
  

   into 
  a 
  chamber 
  (D) 
  which 
  will 
  be 
  called 
  the 
  collar 
  chamber 
  ; 
  this 
  cavity 
  extends 
  on 
  

   ^ach 
  side 
  (figs 
  3 
  and 
  4), 
  and 
  is 
  well 
  shown 
  in 
  section 
  on 
  Plate 
  VII, 
  figs. 
  5, 
  6, 
  11 
  and 
  12. 
  

   From 
  the 
  base 
  of 
  the 
  collar 
  chamber 
  in 
  the 
  median 
  part 
  arise 
  two 
  jaws 
  for 
  closing 
  the 
  

   entrance 
  to 
  the 
  tracheal 
  trunk 
  — 
  a 
  ventral 
  and 
  a 
  dorsal. 
  The 
  ventral 
  jaw 
  (Plates 
  VI, 
  

   VII, 
  VIII-A) 
  is 
  only 
  strongly 
  chitinised 
  on 
  the 
  surface 
  nearest 
  the 
  aperture 
  (Plate 
  VII, 
  

   figs. 
  7-10, 
  A). 
  The 
  dorsal 
  jaw 
  (Plates 
  VI, 
  VII, 
  VIII-B) 
  is 
  strongly 
  chitinised 
  on 
  both 
  

   surfaces 
  and 
  is 
  rigid 
  ; 
  it 
  is 
  always 
  placed 
  behind 
  the 
  ventral 
  jaw 
  (Plate 
  VII, 
  figs. 
  7-10). 
  

   In 
  fig. 
  3 
  on 
  Plate 
  VI, 
  the 
  spiracle 
  has 
  been 
  pressed 
  somewhat, 
  so 
  that 
  jaw 
  A 
  does 
  not 
  

   appear 
  to 
  be 
  in 
  front 
  of 
  jaw 
  B. 
  The 
  dorsal 
  jaw 
  is 
  semi-circular 
  (Plate 
  VI, 
  fig. 
  4) 
  and 
  

   «nds 
  in 
  two 
  processes 
  (E) 
  which 
  apparently 
  are 
  attached 
  to 
  muscles 
  in 
  connection 
  

   with 
  the 
  muscle 
  plate, 
  as 
  is 
  indicated 
  in 
  the 
  section 
  figured 
  on 
  Plate 
  VIII, 
  fig. 
  16. 
  

  

  The 
  two 
  jaws 
  guard 
  the 
  entrance 
  to 
  the 
  tracheal 
  tube, 
  but 
  lead 
  first 
  into 
  a 
  cavity 
  

   (Plate 
  VII, 
  fig. 
  8 
  ; 
  Plate 
  VIII, 
  fig. 
  16, 
  F), 
  in 
  the 
  ventral 
  wall 
  of 
  which 
  muscles 
  (M) 
  are 
  

   inserted 
  ; 
  these 
  muscles 
  are 
  attached 
  at 
  their 
  other 
  extremities 
  to 
  the 
  muscle 
  plate 
  ; 
  

   they 
  are 
  extremely 
  well-developed 
  and 
  almost 
  certainly 
  cause 
  by 
  their 
  con- 
  

   traction 
  the 
  closure 
  of 
  the 
  spiracle. 
  Upon 
  contraction 
  the 
  ventral 
  jaw 
  (A) 
  (which 
  

   as 
  stated 
  above 
  is 
  only 
  strongly 
  chitinised 
  on 
  its 
  outer 
  surface) 
  is 
  pulled 
  down 
  on 
  to 
  

   the 
  dorsal 
  jaw 
  (B) 
  which 
  is 
  practically 
  rigid, 
  and 
  the 
  closure 
  of 
  the 
  aperture 
  effected. 
  

   In 
  some 
  sections 
  obtained 
  the 
  two 
  jaws 
  are 
  in 
  apposition, 
  and 
  this 
  lends 
  support 
  to 
  the 
  

   above 
  statement. 
  It 
  is 
  very 
  probable 
  that 
  the 
  two 
  processes 
  of 
  the 
  dorsal 
  jaw 
  (E- 
  

   Plate 
  VI, 
  fig 
  4 
  ; 
  Plate 
  VIII, 
  fig 
  16), 
  mentioned 
  above 
  as 
  being 
  attached 
  to 
  the 
  closing 
  

   muscles, 
  are 
  pulled 
  inwards 
  and 
  thus 
  cause 
  a 
  more 
  effective 
  closure 
  of 
  the 
  aperture. 
  

  

  The 
  tracheal 
  trunk 
  arises 
  from 
  the 
  cavity 
  F 
  and 
  immediately 
  branches 
  (Plate 
  VI, 
  

   fig 
  3). 
  It 
  is 
  at 
  first 
  surrounded 
  by 
  a 
  layer 
  of 
  cells 
  with 
  large 
  nuclei. 
  

  

  On 
  Plate 
  VIII, 
  fig. 
  21, 
  is 
  a 
  reconstruction 
  intended 
  to 
  show 
  the 
  relations 
  of 
  the 
  

   transverse 
  series 
  of 
  sections 
  to 
  a 
  longitudinal 
  section. 
  It 
  explains 
  the 
  peculiar 
  appear- 
  

  

  *A11 
  the 
  sections 
  were 
  cut 
  in 
  the 
  summer 
  months, 
  

  

  