﻿HOW 
  INSECTS 
  FLY 
  SNODGRASS 
  

  

  413 
  

  

  The 
  flexing 
  of 
  the 
  wing 
  becomes 
  a 
  still 
  more 
  complicated 
  process 
  if 
  

   the 
  vannal 
  region 
  is 
  particularly 
  enlarged. 
  In 
  some 
  of 
  the 
  Orthoptera, 
  

   including 
  most 
  of 
  the 
  cockroaches, 
  the 
  grasshoppers, 
  and 
  the 
  crickets, 
  

   and 
  in 
  some 
  other 
  insects, 
  the 
  vannus 
  of 
  each 
  hind 
  wing 
  is 
  so 
  much 
  

   expanded 
  (fig. 
  15 
  B) 
  that, 
  when 
  the 
  wing 
  is 
  flexed, 
  it 
  must 
  be 
  plaited 
  

   and 
  folded 
  up 
  like 
  a 
  fan 
  (fig. 
  23 
  B) 
  in 
  order 
  to 
  give 
  space 
  for 
  the 
  rest 
  of 
  

   the 
  wing. 
  In 
  wings 
  that 
  are 
  plaited 
  during 
  flexion 
  there 
  may 
  be, 
  as 
  

   in 
  the 
  hiud 
  wing 
  of 
  a 
  grasshopper, 
  two 
  lines 
  of 
  folding 
  between 
  the 
  

   remigium 
  and 
  the 
  vannus 
  with 
  a 
  dividing 
  vein, 
  or 
  vena 
  dividens, 
  

   between 
  them. 
  (Fig. 
  15 
  B, 
  Vd.) 
  The 
  folding 
  and 
  plaiting 
  of 
  the 
  fully 
  

   flexed 
  wings 
  of 
  a 
  grasshopper 
  are 
  shown 
  in 
  Figure 
  23. 
  The 
  narrower 
  

  

  vf^ 
  iV 
  2V 
  sV 
  

  

  Vd 
  . 
  vf 
  

  

  2CU 
  

  

  _--^iCu 
  

  

  R+M 
  

  

  S" 
  

  

  Figure 
  23.— 
  Cross 
  sections 
  through 
  the 
  folded 
  wings 
  of 
  a 
  grasshopper 
  (Dissosteira) 
  _ 
  

   A, 
  Cross 
  section 
  through 
  the 
  wings 
  and 
  the 
  abdomen; 
  the 
  forewings, 
  or 
  tegmina 
  

   (Wi), 
  when 
  closed, 
  form 
  a 
  compartment 
  over 
  the 
  back 
  ( 
  T) 
  in 
  which 
  are 
  folded 
  the 
  

   large 
  hind 
  wings 
  (Wz); 
  B, 
  cross 
  section 
  of 
  the 
  right 
  hind 
  wing, 
  posterior 
  view, 
  

   showing 
  the 
  many 
  plaits 
  of 
  the 
  vannal 
  region 
  ( 
  V) 
  which 
  is 
  folded 
  like 
  a 
  fan. 
  Let- 
  

   tering 
  as 
  on 
  Figure 
  15 
  

  

  forewings, 
  or 
  tegmina 
  (A, 
  Wo), 
  overlap 
  each 
  other 
  to 
  form 
  a 
  rooflike 
  

   covering 
  with 
  steeply 
  slopmg 
  sides 
  completely 
  inclosing 
  and 
  protect- 
  

   ing 
  the 
  more 
  delicate 
  hind 
  wings 
  (IF3) 
  folded 
  beneath 
  them. 
  

  

  The 
  extension 
  of 
  the 
  wing 
  involves 
  a 
  reversal 
  of 
  the 
  movements 
  of 
  

   flexion. 
  The 
  flexor 
  muscle 
  must 
  first 
  relax. 
  A 
  contraction 
  then 
  of 
  the 
  

   anterior 
  pleural 
  muscles 
  (figs. 
  13, 
  19, 
  E, 
  M'), 
  pulling 
  on 
  the 
  humeral 
  

   angle 
  of 
  the 
  wing 
  base, 
  may 
  extend 
  the 
  wing 
  directly, 
  though 
  the 
  action 
  

   of 
  these 
  muscles 
  in 
  this 
  capacity 
  is 
  often 
  difficult 
  to 
  demonstrate 
  in 
  a 
  

   dead 
  specimen. 
  With 
  insects 
  in 
  which 
  the 
  second 
  axillary 
  sclerite 
  is 
  

   elevated 
  on 
  the 
  outer 
  edge 
  of 
  the 
  first 
  axillary 
  in 
  the 
  fully 
  flexed 
  wing, 
  

   it 
  is 
  clear 
  that 
  the 
  wing 
  may 
  be 
  extended 
  by 
  the 
  downward 
  pull 
  of 
  the 
  

   posterior 
  pleural 
  muscle 
  (M') 
  on 
  the 
  second 
  axillary, 
  for 
  a 
  pressure 
  on 
  

   this 
  sclerite 
  at 
  once 
  restores 
  all 
  the 
  axillary 
  elements 
  to 
  a 
  horizontal 
  

  

  