﻿386 
  

  

  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  192 
  9 
  

  

  X^ 
  

  

  ferences. 
  In 
  bodily 
  form 
  and 
  structure 
  there 
  was 
  nothing 
  to 
  dis- 
  

   tinguish 
  a 
  Carboniferous 
  insect 
  from 
  one 
  of 
  its 
  modern 
  descendants 
  ; 
  

   the 
  oldest 
  species 
  known 
  had 
  a 
  head, 
  a 
  thorax, 
  and 
  an 
  abdomen, 
  with 
  

   four 
  wings 
  and 
  six 
  legs 
  carried 
  by 
  the 
  thorax. 
  

  

  One 
  important 
  conclusion, 
  therefore, 
  that 
  we 
  must 
  draw 
  from 
  a 
  

   study 
  of 
  the 
  Carboniferous 
  insects 
  is 
  that 
  they 
  do 
  not 
  by 
  any 
  means 
  

   represent 
  the 
  primitive 
  ancestors 
  of 
  insects. 
  Having 
  already 
  fully 
  

   developed 
  wings, 
  the 
  Carboniferous 
  insects 
  themselves 
  must 
  have 
  been 
  

   evolved 
  during 
  millions 
  of 
  years 
  preceding 
  their 
  time 
  from 
  wingless 
  

   forms 
  of 
  which 
  we 
  have 
  no 
  record. 
  Any 
  attempt 
  to 
  explain 
  the 
  genesis 
  

  

  of 
  insect 
  wings, 
  then, 
  must 
  be 
  purely 
  con- 
  

   jectural, 
  but 
  we 
  may 
  arrive 
  at 
  a 
  fairly 
  sat- 
  

   isfactory 
  conclusion 
  concerning 
  their 
  origin 
  

   by 
  a 
  study 
  of 
  the 
  wings 
  themselves 
  and 
  the 
  

   thoracic 
  segments 
  that 
  support 
  them. 
  In 
  

   one 
  feature, 
  however, 
  some 
  of 
  the 
  ancient 
  

   insects 
  do 
  give 
  us 
  a 
  slight 
  clew 
  to 
  the 
  pos- 
  

   sible 
  nature 
  of 
  the 
  primitive 
  wings, 
  as 
  we 
  

   shall 
  see 
  presently. 
  

  

  The 
  wings 
  of 
  all 
  modern 
  insects 
  are 
  car- 
  

   ried 
  by 
  the 
  second 
  and 
  third 
  segments 
  of 
  

   the 
  thorax. 
  Structurally 
  they 
  are 
  flat 
  out- 
  

   growths 
  of 
  the 
  lateral 
  edges 
  of 
  the 
  back 
  

   plates 
  of 
  these 
  segments. 
  In 
  their 
  develop- 
  

   ment 
  they 
  begin 
  as 
  flat 
  pads 
  or 
  pouchlike 
  

   outgrowths 
  of 
  the 
  body 
  wall, 
  the 
  two 
  layers 
  

   of 
  which 
  eventually 
  come 
  together 
  and 
  form 
  

   the 
  upper 
  and 
  lower 
  surfaces 
  of 
  the 
  mature 
  

   wing. 
  Semitubular 
  thickenings 
  of 
  the 
  op- 
  

   posed 
  surfaces 
  give 
  rise 
  to 
  the 
  veins. 
  The 
  

   canals 
  of 
  the 
  veins 
  represent, 
  therefore, 
  the 
  

   remnants 
  of 
  the 
  original 
  wing 
  cavity, 
  and 
  

   they 
  contain 
  the 
  tracheae, 
  nerves, 
  and 
  blood 
  

   of 
  the 
  wings. 
  

  

  Among 
  the 
  Carboniferous 
  insects 
  there 
  

   are 
  frequently 
  found 
  species 
  which 
  have 
  

   a 
  pair 
  of 
  small, 
  flat 
  lobes 
  resembhng 
  the 
  

   developing 
  wing 
  pads, 
  which 
  extend 
  laterally 
  from 
  the 
  margins 
  of 
  the 
  

   first 
  segment 
  of 
  the 
  thorax, 
  or 
  prothorax. 
  (Fig. 
  2 
  A, 
  B, 
  ^^Ti/. 
  ) 
  These 
  pro- 
  

   thoracic 
  lobes 
  suggest, 
  therefore, 
  that 
  the 
  wings 
  have 
  been 
  evolved 
  from 
  

   similar 
  lobes 
  on 
  the 
  mesothorax 
  and 
  meta 
  thorax. 
  There 
  is 
  no 
  evidence 
  

   to 
  suggest 
  the 
  improbable 
  view 
  that 
  insects 
  ever 
  had 
  three 
  pairs 
  of 
  

   fully 
  developed 
  wings 
  used 
  for 
  flight; 
  but 
  we 
  may 
  assume 
  that 
  three 
  

   pairs 
  of 
  flaps, 
  or 
  paranotai 
  lobes 
  as 
  they 
  have 
  been 
  termed, 
  forming 
  a 
  

   series 
  of 
  overlapping 
  plates 
  on 
  each 
  side 
  of 
  the 
  thorax 
  (fig. 
  3), 
  

  

  Figure 
  3.— 
  A 
  suggestion 
  of 
  the 
  pos- 
  

   sible 
  structure 
  of 
  a 
  primitive 
  in- 
  

   sect 
  provided 
  with 
  three 
  pairs 
  of 
  

   glider 
  lobes, 
  or 
  lateral 
  extensions 
  

   of 
  the 
  back 
  plates 
  of 
  the 
  thoracic 
  

   segments 
  

  

  