﻿396 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  19 
  29 
  

  

  half 
  of 
  the 
  lateral 
  edge 
  of 
  the 
  tergum, 
  or 
  back 
  plate 
  (T), 
  of 
  the 
  segment 
  

   supporting 
  the 
  wings, 
  or 
  sometimes 
  to 
  a 
  distinct 
  sclerite 
  (a) 
  of 
  the 
  

   tergum. 
  The 
  axillary 
  plate 
  is 
  articulated 
  to 
  the 
  posterior 
  half 
  of 
  the 
  

   lateral 
  tergal 
  margin 
  opposite 
  a 
  deep 
  membranous 
  area 
  of 
  the 
  latter. 
  

   The 
  wing 
  base 
  is 
  supported 
  from 
  below 
  by 
  the 
  v/ing 
  process 
  of 
  the 
  

   pleural 
  wall 
  of 
  the 
  segment, 
  one 
  branch 
  of 
  it 
  articulating 
  with 
  the 
  

   humeral 
  plate, 
  another 
  with 
  the 
  axillary 
  plate. 
  

  

  The 
  basal 
  plates 
  of 
  the 
  dragon 
  fly's 
  wing 
  turn 
  up 
  and 
  down 
  on 
  the 
  

   fulcral 
  arms 
  when 
  the 
  wings 
  are 
  lifted 
  or 
  depressed. 
  The 
  two 
  plates, 
  

   however, 
  are 
  slightly 
  movable 
  on 
  each 
  other, 
  and, 
  since 
  the 
  costal 
  vein 
  

   (CO 
  is 
  doubly 
  hinged 
  to 
  the 
  humeral 
  plate 
  by 
  the 
  small 
  intermediary 
  

   piece 
  (c) 
  at 
  its 
  base, 
  the 
  costal 
  area 
  of 
  the 
  wing 
  can 
  be 
  quite 
  freely 
  

   deflected 
  independent 
  of 
  the 
  rest 
  of 
  the 
  wing 
  area, 
  which 
  is 
  solidly 
  

   supported 
  on 
  the 
  axillary 
  plate 
  by 
  the 
  veins 
  attached 
  to 
  the 
  latter. 
  

  

  The 
  Ma}^ 
  flies, 
  or 
  Ephemerida, 
  are 
  the 
  only 
  other 
  order 
  of 
  modern 
  

   insects 
  that 
  do 
  not 
  flex 
  the 
  wings. 
  At 
  first 
  sight 
  the 
  base 
  of 
  the 
  

   Mayfly's 
  wing 
  (fig. 
  11 
  B) 
  appears 
  to 
  have 
  little 
  in 
  common 
  with 
  that 
  of 
  

   the 
  dragon 
  fly 
  (A). 
  On 
  closer 
  inspection, 
  however, 
  it 
  is 
  seen 
  that 
  the 
  

   chief 
  difference 
  consists 
  of 
  a 
  great 
  reduction 
  in 
  size 
  of 
  the 
  humeral 
  

   plate 
  (HP), 
  and 
  a 
  breaking 
  up 
  of 
  the 
  region 
  of 
  the 
  axillarj' 
  plate 
  {AxP) 
  

   into 
  a 
  number 
  of 
  irregular 
  sclerotizations. 
  The 
  humeral 
  plate 
  (HP) 
  

   becomes 
  a 
  small 
  sclerite 
  on 
  the 
  anterior 
  margin 
  of 
  the 
  wing 
  base 
  inter- 
  

   mediating 
  between 
  the 
  base 
  of 
  the 
  costal 
  vein 
  (C) 
  and 
  a 
  small 
  lobe 
  of 
  

   the 
  dorsal 
  wall 
  of 
  the 
  segment 
  supporting 
  the 
  wing. 
  The 
  small 
  

   plates 
  of 
  the 
  axillary 
  region 
  (Ax) 
  in 
  the 
  May 
  fly 
  suggest, 
  as 
  we 
  shall 
  

   presently 
  see, 
  the 
  definite 
  sclerites 
  of 
  the 
  flexor 
  mechanism 
  in 
  insects 
  

   that 
  fold 
  the 
  wings 
  horizontally 
  over 
  the 
  back. 
  

  

  In 
  all 
  insects 
  that 
  flex 
  the 
  wings, 
  the 
  major 
  part 
  of 
  thf 
  wing 
  base 
  

   is 
  occupied 
  by 
  a 
  number 
  of 
  small 
  sclerites 
  which 
  lie 
  between 
  the 
  edge 
  

   of 
  the 
  supporting 
  tergum 
  and 
  the 
  proximal 
  ends 
  of 
  the 
  veins. 
  These 
  

   axillary 
  sclerites, 
  or 
  axillaries 
  (fig. 
  12), 
  have 
  definite 
  and 
  constant 
  

   relations 
  not 
  only 
  to 
  the 
  tergum 
  and 
  the 
  veins, 
  but 
  also 
  to 
  one 
  another, 
  

   though 
  they 
  vary 
  much 
  in 
  details 
  of 
  form, 
  and 
  certain 
  pieces 
  are 
  

   sometimes 
  lacking. 
  Three 
  sclerites, 
  however, 
  are 
  practically 
  always 
  

   present 
  (lAx, 
  2 
  Ax, 
  3 
  Ax), 
  and 
  in 
  some 
  insects 
  there 
  is 
  a 
  fourth 
  (fig. 
  

   10 
  B, 
  4-Ax), 
  while 
  at 
  least 
  one 
  or 
  two 
  accessory 
  plates 
  (fig. 
  12, 
  m, 
  m') 
  

   are 
  usually 
  associated 
  with 
  the 
  more 
  constant 
  sclerites. 
  The 
  humeral 
  

   plate 
  of 
  the 
  wing 
  base 
  is 
  generalh^ 
  small 
  (HP), 
  and 
  may 
  be 
  absent, 
  

   but 
  it 
  is 
  often 
  relatively 
  large 
  though 
  never 
  attaining 
  the 
  size 
  it 
  has 
  

   in 
  the 
  wing 
  of 
  a 
  dragon 
  flj^ 
  (fig. 
  11 
  A, 
  HP). 
  When 
  the 
  humeral 
  

   plate 
  is 
  present 
  the 
  costal 
  vein 
  (CO 
  is 
  associated 
  with 
  it. 
  The 
  other 
  

   veins 
  are 
  related 
  to 
  the 
  sclerites 
  of 
  the 
  true 
  axillary 
  region. 
  

  

  The 
  axillary 
  sclerites 
  have 
  in 
  general 
  the 
  following 
  characteristics 
  

   and 
  relationships: 
  The 
  ^rst 
  axillary 
  (fig. 
  12, 
  lAx) 
  lies 
  next 
  to 
  the 
  

   body 
  in 
  the 
  anterior 
  part 
  of 
  the 
  axillary 
  region 
  of 
  the 
  wing 
  base, 
  and 
  is 
  

  

  