﻿HOW 
  INSECTS 
  FLY 
  SNODGEASS 
  401 
  

  

  enables 
  the 
  insects 
  to 
  sail 
  through 
  the 
  air 
  wdth 
  comparatively 
  little 
  

   movement 
  of 
  the 
  wings. 
  Proximal 
  to 
  the 
  vannus 
  is 
  the 
  jugal 
  region 
  

   (fig. 
  14, 
  Ju), 
  usuall}^ 
  a 
  small 
  membranous 
  area 
  or 
  lobe 
  at 
  the 
  base 
  of 
  

   the 
  wing, 
  but 
  sometimes 
  much 
  enlarged 
  (fig. 
  16). 
  

  

  III. 
  THE 
  WING 
  MUSCLES 
  

  

  The 
  nmsculature 
  of 
  an 
  insect's 
  wdng 
  is 
  very 
  simple, 
  considering 
  the 
  

   nature 
  of 
  the 
  wing 
  movements 
  and 
  the 
  fine 
  adjustments 
  of 
  the 
  latter 
  

   that 
  the 
  muscles 
  are 
  able 
  to 
  produce. 
  The 
  effect 
  of 
  the 
  muscles 
  on 
  the 
  

   wings 
  depends 
  largely 
  on 
  the 
  maimer 
  in 
  which 
  the 
  wings 
  are 
  attached 
  

   to 
  the 
  body 
  and 
  on 
  the 
  details 
  of 
  structure 
  in 
  the 
  wings 
  themselves. 
  

  

  In 
  the 
  majority 
  of 
  insects, 
  all 
  the 
  movements 
  of 
  the 
  wings 
  are 
  

   accomplished 
  b}^ 
  five 
  principal 
  pairs, 
  or 
  paired 
  sets, 
  of 
  muscles 
  in 
  each 
  

   wing 
  segment. 
  Anatomically 
  the 
  wing 
  muscles 
  belong 
  to 
  three 
  

   groups, 
  namely, 
  dorsal 
  longitudinal 
  muscles, 
  tergo-stemal 
  muscles, 
  and 
  

   pleural 
  muscles. 
  Considering 
  the 
  manner 
  in 
  which 
  they 
  effect 
  move- 
  

  

  C 
  Sc 
  K 
  C+Sc+Ri 
  

  

  FiGUPE 
  16.— 
  Hind 
  wing 
  of 
  a 
  blister 
  beetle 
  {Epicaitta 
  marginata), 
  showing 
  the 
  large 
  

   jugal 
  region 
  (J'a) 
  

  

  ment 
  in 
  the 
  wings, 
  however, 
  they 
  are 
  usually 
  classed 
  as 
  ** 
  indirect 
  wing 
  

   muscles" 
  and 
  ''direct 
  wing 
  muscles," 
  the 
  first 
  class 
  being 
  the 
  dorsal 
  

   and 
  tergo-sternal 
  muscles, 
  the 
  second 
  the 
  pleural 
  m.uscles. 
  Function- 
  

   ally, 
  each 
  of 
  the 
  five 
  sets 
  of 
  muscles 
  must 
  be 
  considered 
  individually. 
  

   If 
  the 
  wings 
  of 
  insects 
  originated, 
  as 
  we 
  have 
  supposed, 
  from 
  

   movable 
  flaps 
  of 
  the 
  body 
  wall 
  extending 
  laterally 
  from 
  the 
  edges 
  of 
  

   the 
  back 
  plates 
  of 
  the 
  body 
  (fig. 
  6), 
  they 
  had 
  primarily 
  at 
  their 
  dis- 
  

   posal 
  for 
  motor 
  purposes 
  only 
  the 
  muscles 
  of 
  the 
  body 
  segments 
  

   supporting 
  them. 
  These 
  muscles 
  comprised 
  the 
  longitudinal 
  inter- 
  

   segmental 
  muscles, 
  and 
  possibly 
  dorso 
  ventral 
  intrasegmental 
  muscles. 
  

   The 
  dorsal 
  longitudinal 
  muscles, 
  by 
  pulling 
  lengthwise 
  on 
  the 
  back- 
  

   plates, 
  could 
  arch 
  these 
  plates 
  upward 
  between 
  the 
  two 
  ends 
  in 
  each 
  

   segment. 
  Thus, 
  considering 
  that 
  the 
  wing 
  lobes 
  were 
  extensions 
  of 
  

   the^terga, 
  and 
  were 
  supported 
  near 
  their 
  bases 
  on 
  the 
  upper 
  edges 
  of 
  

   the 
  pleural 
  waUs 
  of 
  the 
  segment, 
  each 
  lobe 
  could 
  be 
  given 
  a 
  downward 
  

   movement 
  by 
  an 
  upward 
  flexure 
  of 
  the 
  tergum 
  just 
  as 
  a 
  pump 
  handle 
  

  

  