﻿HOW 
  INSECTS 
  FLY 
  SNODGTIASS 
  

  

  391 
  

  

  and 
  they 
  often 
  make 
  long 
  excursions 
  inland, 
  appearing 
  in 
  places 
  where 
  

   a 
  dragon 
  fly 
  is 
  least 
  expected. 
  So 
  agile 
  are 
  they 
  on 
  the 
  wing 
  that 
  tha 
  

   collector 
  must 
  sometimes 
  resort 
  to 
  the 
  gun 
  and 
  bird 
  shot 
  to 
  procure 
  

   specimens 
  of 
  them. 
  

  

  The 
  May 
  flies 
  are 
  members 
  of 
  the 
  order 
  Ephemerida. 
  They 
  are 
  

   mostly 
  fragile, 
  short-lived 
  creatures 
  in 
  the 
  adult 
  stage, 
  and 
  when 
  at 
  

   rest 
  fold 
  the 
  wings 
  straight 
  up 
  over 
  the 
  back 
  with 
  the 
  dorsal 
  surfaces 
  

   together. 
  (Fig. 
  9.) 
  

  

  All 
  other 
  modern 
  winged 
  insects, 
  with 
  a 
  few 
  exceptions 
  such 
  as 
  the 
  

   butterflies, 
  fold 
  the 
  wings 
  posteriorly 
  and 
  horizontally 
  over 
  the 
  body 
  

   when 
  they 
  are 
  not 
  

  

  in 
  use. 
  This 
  man- 
  ^^^^5t>^ 
  ^^P? 
  

  

  ner 
  of 
  folding 
  the 
  

   wings 
  may 
  be 
  dis- 
  

   tinguished 
  a 
  s 
  flexion 
  . 
  

   It 
  is 
  quite 
  different 
  

   from 
  the 
  other, 
  in 
  

   which 
  the 
  extended 
  

   wings 
  are 
  merely 
  

   brought 
  together 
  

   vertically 
  over 
  the 
  

   back, 
  and 
  it 
  involves 
  

   the 
  presence 
  of 
  a 
  

   special 
  mechanism 
  

   of 
  flexion 
  which 
  the 
  

   dragon 
  flies 
  and 
  May 
  

   flies 
  do 
  not 
  possess. 
  

  

  Since 
  the 
  wing- 
  

   flexor 
  apparatus 
  has 
  

   very 
  evidently 
  been 
  

   added 
  to 
  that 
  which 
  

   produces 
  the 
  move- 
  

   ments 
  of 
  flight, 
  it 
  

   is 
  usually 
  supposed 
  

   that 
  the 
  insects 
  

   which 
  do 
  not 
  flex 
  the 
  

   wings 
  are 
  descend- 
  

   ants 
  of 
  a 
  more 
  primitive 
  group 
  of 
  ancestral 
  insects 
  than 
  are 
  tho.'e 
  which 
  

   flex 
  the 
  wings. 
  The 
  fundamental 
  structure 
  of 
  the 
  wings 
  we 
  might 
  sus- 
  

   pect, 
  therefore, 
  would 
  be 
  best 
  preserved 
  in 
  the 
  wings 
  of 
  the 
  dragon 
  flies 
  

   and 
  May 
  flies; 
  but 
  it 
  is 
  certain 
  that 
  these 
  insects, 
  though 
  of 
  relatively 
  

   primitive 
  origin, 
  have 
  developed 
  many 
  specialized 
  characters 
  of 
  their 
  

   own. 
  Particularly 
  is 
  this 
  true 
  of 
  the 
  dragon 
  flies. 
  The^structure 
  of 
  a 
  

   "generalized" 
  wing, 
  then, 
  is 
  to 
  be 
  judged 
  rather 
  fromUhe 
  ensemble 
  

   of 
  the 
  wing 
  characters 
  in 
  all 
  insects 
  than 
  from 
  a 
  study 
  of 
  the 
  wings 
  of 
  

   any 
  particular 
  group 
  of 
  insects. 
  

  

  Figure 
  S.— 
  Dragon 
  flies 
  of 
  the 
  suborder 
  Zygoptera, 
  called 
  damsel 
  flies, 
  

   which, 
  when 
  at 
  rest, 
  fold 
  the 
  wings 
  in 
  a 
  vertical 
  plane 
  over 
  the 
  back 
  

   (Ischnura 
  cermda, 
  from 
  Kennedy) 
  

  

  