﻿394 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  19 
  2 
  9 
  

  

  vannus, 
  a 
  fan), 
  distinguishing 
  them 
  individually 
  as 
  the 
  first 
  vannal 
  

   (fig. 
  10 
  B, 
  IV), 
  second 
  vannal 
  {2V)^ 
  etc. 
  

  

  The 
  innermost 
  part 
  of 
  the 
  wing 
  proximal 
  to 
  the 
  region 
  of 
  the 
  vannal 
  

   veins 
  is 
  often 
  difl'erentiated 
  as 
  a 
  lobe 
  or 
  a 
  distinct 
  part 
  of 
  the 
  wing 
  

   designated 
  by 
  Martynov 
  (1925) 
  the 
  jugal 
  region 
  because 
  in 
  the 
  fore 
  

   wing 
  it 
  sometimes 
  bears 
  a 
  small 
  lobe, 
  or 
  jugum, 
  serving 
  to 
  yoke 
  the 
  

   fore 
  and 
  hind 
  wings 
  together. 
  In 
  this 
  region 
  there 
  is 
  sometimes 
  a 
  

   network 
  of 
  irregular 
  veins, 
  but 
  again 
  the 
  jugal 
  region 
  may 
  contain 
  

   one 
  or 
  two 
  quite 
  definite 
  veins, 
  named 
  the 
  vena 
  arcuata 
  (fig. 
  10 
  B, 
  Va) 
  

   and 
  vena 
  cardinalis 
  (Vc) 
  by 
  Martynov. 
  

  

  The 
  area 
  of 
  the 
  wing 
  containing 
  the 
  veins 
  may 
  be 
  thus 
  divided, 
  es- 
  

   pecially 
  in 
  the 
  wing-flexing 
  insects, 
  into 
  three 
  regions. 
  The 
  first 
  is 
  

   the 
  prevanna] 
  region, 
  or 
  remigium, 
  the 
  second 
  is 
  the 
  vannal 
  region, 
  

   the 
  third 
  the 
  jugal 
  region. 
  (Fig. 
  14.) 
  The 
  remigium 
  and 
  the 
  vannus 
  

   are 
  often 
  separated 
  b}' 
  a 
  vannal 
  fold, 
  or 
  plica 
  vannalis 
  (fig. 
  10 
  B, 
  vf), 
  

   while 
  the 
  vannal 
  and 
  jugal 
  regions 
  are 
  separated 
  by 
  a 
  jugal 
  fold, 
  or 
  

   plica 
  jugalis 
  (jf). 
  The 
  vannal 
  fold, 
  however, 
  is 
  sometimes 
  doubly 
  

   plicate, 
  and 
  a 
  secondary 
  vein, 
  the 
  vena 
  dividens 
  (fig. 
  15 
  B, 
  Vd), 
  then 
  

   lies 
  between 
  the 
  two 
  lines 
  of 
  plication. 
  This 
  concept 
  of 
  the 
  structure 
  

   of 
  the 
  posterior 
  part 
  of 
  the 
  wing 
  will 
  at 
  least 
  serve 
  for 
  purposes 
  of 
  

   description 
  in 
  the 
  present 
  paper, 
  but 
  it 
  is 
  possible 
  that 
  a 
  more 
  com- 
  

   prehensive 
  study 
  of 
  the 
  wing 
  in 
  generalized 
  insects 
  will 
  reveal 
  that 
  we 
  

   do 
  not 
  yet 
  understand 
  the 
  true 
  homologies 
  of 
  the 
  veins 
  in 
  the 
  post- 
  

   cubital 
  region. 
  

  

  All 
  the 
  veins 
  of 
  the 
  wing 
  are 
  subject 
  to 
  secondary 
  forking 
  and 
  to 
  

   union 
  by 
  cross 
  veins. 
  In 
  some 
  orders 
  of 
  insects 
  the 
  cross-veins 
  are 
  so 
  

   numerous 
  that 
  the 
  whole 
  venational 
  pattern 
  becomes 
  a 
  close 
  network 
  

   of 
  veins 
  and 
  cross 
  veins. 
  (Figs. 
  7, 
  8, 
  9.) 
  Ordinarily, 
  however, 
  there 
  

   is 
  a 
  definite 
  number 
  of 
  cross 
  veins 
  having 
  specific 
  locations 
  as 
  indicated 
  

   in 
  the 
  diagram. 
  (Fig. 
  10 
  A.) 
  

  

  Articulation 
  of 
  the 
  wings. 
  — 
  The 
  simplest 
  structure 
  in 
  the 
  articular 
  

   parts 
  of 
  the 
  wing 
  is 
  that 
  shown 
  by 
  the 
  dragon 
  flies 
  and 
  May 
  flies, 
  

   since 
  the 
  wings 
  of 
  these 
  insects 
  are 
  adapted 
  to 
  movements 
  of 
  flight 
  

   only, 
  and, 
  as 
  a 
  consequence, 
  possess 
  only 
  the 
  flight 
  mechanism. 
  In 
  

   the 
  wings 
  of 
  insects 
  that 
  flex 
  the 
  wings, 
  there 
  is 
  superadded 
  to 
  the 
  

   apparatus 
  of 
  flight 
  a 
  mechanism 
  for 
  folding 
  the 
  wings. 
  The 
  dragon 
  

   fhes 
  and 
  May 
  flies 
  are 
  commonly 
  regarded 
  as 
  being 
  descendants 
  of 
  a 
  

   more 
  primitive 
  ancestral 
  stock 
  than 
  that 
  of 
  the 
  wing-flexing 
  insects; 
  

   but 
  the 
  question 
  as 
  to 
  whether 
  their 
  articular 
  mechanism 
  is 
  primitive, 
  

   or 
  derived 
  from 
  a 
  more 
  complicated 
  mechanism, 
  will 
  not 
  be 
  discussed 
  

   here. 
  The 
  dragon 
  fly 
  wing 
  base 
  m&j 
  be 
  taken 
  as 
  a 
  starting 
  point 
  in 
  

   a 
  descriptive 
  sequence, 
  however, 
  because 
  of 
  its 
  simplicity. 
  

  

  Each 
  wing 
  of 
  a 
  dragon 
  fly 
  is 
  attached 
  to 
  the 
  body 
  by 
  two 
  large 
  basal 
  

   plates. 
  (Fig. 
  11 
  A.) 
  The 
  first 
  plate 
  we 
  may 
  call 
  the 
  humeral 
  plate 
  

   (HP), 
  the 
  second 
  the 
  axillary 
  plate 
  {AxP). 
  The 
  humeral 
  plate, 
  

  

  