﻿410 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1929 
  

  

  the 
  remigium 
  {Rm) 
  by 
  a 
  vannal 
  fold, 
  or 
  plica 
  {vj), 
  and 
  the 
  jugal 
  lobe 
  

   {Ju) 
  is 
  separated 
  from 
  the 
  vannus 
  by 
  a 
  jugal 
  plica 
  [jj). 
  The 
  axillary 
  

   sclerites 
  are 
  highly 
  variable 
  in 
  form 
  in 
  difi'erent 
  insects, 
  but 
  their 
  

   relationships 
  to 
  one 
  another 
  and 
  to 
  the 
  bases 
  of 
  the 
  veins 
  are 
  constant. 
  

   The 
  articulation 
  of 
  the 
  radial 
  vein 
  (fig. 
  12, 
  R) 
  with 
  the 
  second 
  axillary 
  

   {2Ax) 
  lies 
  at 
  the 
  point 
  d 
  on 
  the 
  anterior 
  side 
  of 
  the 
  axillary 
  triangle 
  

   (fig. 
  22 
  A). 
  The 
  edge 
  of 
  the 
  triangle 
  between 
  this 
  point 
  and 
  the 
  apex 
  

   (c)- 
  is 
  formed 
  by 
  the 
  Hne 
  of 
  flexion, 
  or 
  plica 
  basalis 
  (bf), 
  between 
  the 
  

   median 
  plates 
  of 
  the 
  wing 
  base 
  (fig. 
  12, 
  w, 
  7n'), 
  or 
  between 
  the 
  cor- 
  

   responding 
  areas 
  if 
  the 
  plates 
  are 
  obsolete 
  or 
  absent. 
  The 
  third 
  

   axillary 
  sclerite 
  (fig. 
  12, 
  3 
  Ax) 
  is 
  the 
  crucial 
  piece 
  of 
  the 
  flexor 
  mech- 
  

   anism. 
  Typically 
  it 
  is 
  essentially 
  Y-shaped, 
  the 
  two 
  prongs 
  being 
  

   the 
  arms 
  of 
  the 
  mesal 
  part 
  hinged 
  by 
  their 
  tips 
  (/, 
  6) 
  between 
  the 
  

   second 
  axillary 
  and 
  a 
  posterior 
  process 
  of 
  the 
  tergum, 
  with 
  the 
  flexor 
  

   muscle 
  (D) 
  inserted 
  in 
  the 
  crotch, 
  while 
  the 
  stalk 
  is 
  the 
  distal 
  arm, 
  the 
  

   end 
  of 
  which 
  is 
  closely 
  associated 
  with 
  the 
  bases 
  of 
  the 
  vannal 
  veins 
  

   (IV, 
  2V) 
  at 
  the 
  apex 
  of 
  the 
  axillary 
  triangle. 
  (Fig. 
  22 
  A, 
  c.) 
  

  

  When 
  the 
  muscles 
  that 
  keep 
  the 
  wing 
  extended 
  are 
  relaxed, 
  the 
  

   wing 
  automatically 
  turns 
  a 
  little 
  posteriorly, 
  and 
  a 
  prominent 
  convex 
  

   fold 
  is 
  formed 
  along 
  the 
  oblique 
  plica 
  basalis 
  (fig. 
  12, 
  hj) 
  at 
  the 
  base 
  

   of 
  the 
  medio-cubital 
  field 
  of 
  the 
  wing, 
  which 
  is 
  between 
  the 
  two 
  median 
  

   plates 
  (m, 
  m.') 
  when 
  these 
  plates 
  are 
  present. 
  At 
  the 
  same 
  time, 
  the 
  

   third 
  axillary 
  sclerite 
  {3Ax) 
  is 
  revolved 
  upward 
  on 
  its 
  basal 
  hinge, 
  or 
  

   hinges 
  (6,/), 
  until 
  the 
  insertion 
  point 
  of 
  its 
  muscle 
  {D) 
  lies 
  dorsal 
  and 
  

   slightly 
  mesad 
  to 
  the 
  axis 
  of 
  the 
  hinge. 
  The 
  muscle, 
  which 
  arises 
  on 
  

   the 
  inner 
  wall 
  of 
  the 
  pleuron 
  below 
  the 
  wing 
  base 
  (fig. 
  19, 
  D), 
  thus 
  

   acquires 
  an 
  efTective 
  purchase 
  on 
  the 
  third 
  axillary, 
  and, 
  by 
  contrac- 
  

   tion, 
  it 
  evidently 
  now 
  continues 
  the 
  revolution 
  of 
  the 
  sclerite, 
  turning 
  

   the 
  outer 
  end 
  of 
  the 
  latter 
  (fig. 
  12, 
  c) 
  dorsally, 
  mesally, 
  and 
  forward, 
  

   until 
  the 
  sclerite 
  is 
  completely 
  inverted 
  and 
  reversed 
  in 
  position. 
  

   Concomitant 
  with 
  the 
  movement 
  of 
  the 
  third 
  axillary, 
  the 
  first 
  median 
  

   plate 
  (w), 
  which 
  is 
  usually 
  attached 
  to 
  the 
  latter, 
  turns 
  to 
  a 
  vertical 
  

   position 
  between 
  its 
  hinge 
  with 
  the 
  second 
  axillary 
  {2Ax) 
  and 
  its 
  

   hinge 
  with 
  the 
  second 
  median 
  plate 
  (m'), 
  or 
  with 
  the 
  base 
  of 
  the 
  medio- 
  

   cubital 
  area 
  of 
  the 
  wing, 
  and 
  this 
  line 
  of 
  flexion 
  {hj) 
  is 
  swung 
  inward 
  

   posteriorly 
  imtil 
  it 
  takes 
  an 
  oblique 
  position 
  extending 
  from 
  in 
  front 
  

   posteriorly 
  and 
  mesally, 
  overlapping 
  the 
  posterior 
  part 
  of 
  the 
  second 
  

   axillary. 
  

  

  The 
  movements 
  of 
  the 
  third 
  axillary 
  and 
  the 
  attached 
  median 
  plate 
  

   (m), 
  caused 
  by 
  the 
  contraction 
  of 
  the 
  flexor 
  muscle 
  {D), 
  bring 
  about 
  

   the 
  flexion 
  of 
  the 
  wing 
  and 
  incidentally 
  whatever 
  folding 
  the 
  wing 
  

   surface 
  undergoes 
  during 
  flexion* 
  The 
  mesal 
  revolution 
  of 
  the 
  third 
  

   axillary 
  directly 
  lifts 
  the 
  base 
  of 
  the 
  vannal 
  region 
  of 
  the 
  wiiig 
  asso- 
  

   ciated 
  with 
  the 
  end 
  of 
  its 
  distal 
  arm, 
  and 
  brings 
  it 
  to 
  a 
  mesal 
  position 
  

   against 
  the 
  side 
  of 
  the 
  body. 
  At 
  the 
  same 
  time, 
  the 
  upward 
  revolu- 
  

  

  