﻿406 
  

  

  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  192 
  9 
  

  

  tion 
  of 
  the 
  vertical, 
  tergo-aternal 
  muscles 
  (figs. 
  17 
  A, 
  20, 
  O). 
  The 
  

   mechanism 
  of 
  the 
  upstroke, 
  therefore, 
  is 
  that 
  of 
  a 
  lever 
  of 
  the 
  first 
  

   class, 
  the 
  fulcrum 
  being 
  the 
  pleural 
  wing 
  process 
  (WP) 
  upon 
  which 
  

   the 
  base 
  of 
  the 
  wing 
  rests. 
  The 
  tergo-sternal 
  muscles 
  are 
  often 
  

   large 
  and 
  powerful, 
  suggesting 
  that 
  the 
  upstroke 
  of 
  the 
  wings 
  is 
  an 
  

   important 
  contributant 
  to 
  the 
  force 
  of 
  flight. 
  

  

  The 
  downstroke 
  of 
  the 
  wings 
  is 
  not 
  the 
  work 
  of 
  a 
  single 
  set 
  of 
  

   muscles. 
  It 
  results 
  in 
  part 
  from 
  the 
  restoration 
  of 
  the 
  dorsal 
  curva- 
  

   ture 
  of 
  the 
  back 
  by 
  the 
  contraction 
  of 
  the 
  dorsal 
  longitudinal 
  muscltes 
  

   (fig. 
  17 
  C, 
  20, 
  A; 
  fig. 
  18, 
  81, 
  112), 
  which 
  are 
  the 
  segmental 
  antag- 
  

   onists 
  of 
  the 
  tergosternal 
  muscles; 
  but 
  probably 
  an 
  important 
  effector 
  

  

  of 
  the 
  wing 
  depres- 
  

   sion 
  in 
  most 
  insects 
  

   is 
  the 
  posterior 
  pleu- 
  

   ral 
  muscle 
  (figs. 
  13, 
  

   19, 
  M") 
  inserted 
  on 
  

   the 
  subalar 
  sclerite 
  

   {Sa). 
  The 
  subalar 
  

   sclerite, 
  as 
  we 
  have 
  

   seen, 
  is 
  in 
  immediate 
  

   connection 
  with 
  the 
  

   second 
  axillary 
  of 
  

   the 
  wing 
  base 
  {2 
  Ax), 
  

   and 
  a 
  pull 
  upon 
  the 
  

   subalar 
  muscle 
  

   strongly 
  depresses 
  

   the 
  wing. 
  

  

  The 
  forward 
  and 
  

   rearward 
  move- 
  

   ments 
  of 
  the 
  wing 
  

   during 
  flight 
  are 
  of 
  

   small 
  extent, 
  but 
  of 
  

   m 
  u 
  c 
  h 
  importance 
  . 
  

   They 
  evidently 
  are 
  

   produced 
  by 
  the 
  an- 
  

   terior 
  and 
  posterior 
  pleural 
  muscles 
  (figs. 
  13, 
  19, 
  E, 
  M' 
  , 
  and 
  M") 
  

   pulling 
  on 
  the 
  wing 
  base, 
  respectively 
  before 
  and 
  behind 
  the 
  pleural 
  

   fulcrum 
  {WP). 
  

  

  The 
  rotation 
  of 
  the 
  wing 
  on 
  its 
  long 
  axis 
  accompanies 
  the 
  anterior 
  

   and 
  posterior 
  movements, 
  and 
  is 
  produced 
  by 
  the 
  same 
  muscles, 
  

   namely, 
  the 
  muscles 
  of 
  the 
  basalar 
  and 
  subalar 
  sclerites. 
  The 
  first 
  

   (fig. 
  20, 
  M') 
  pulling 
  downward 
  on 
  the 
  basalare 
  {Ba) 
  turns 
  this 
  sclerite 
  

   inward 
  on 
  the 
  upper 
  edge 
  of 
  the 
  pleuron 
  {PI), 
  and 
  the 
  connection 
  

   (a) 
  of 
  the 
  basalare 
  with 
  the 
  humeral 
  angle 
  of 
  the 
  wing 
  base 
  deflects 
  

  

  Figure 
  20.— 
  Diagram 
  of 
  the 
  "direct" 
  and 
  "indirect 
  " 
  wing 
  muscles 
  in 
  

   left 
  half 
  of 
  a 
  segment, 
  anterior 
  view. 
  A, 
  Section 
  of 
  longitudinal 
  dorsal 
  

   muscle 
  ("indirect" 
  depressor 
  of 
  the 
  wings); 
  a, 
  membranous 
  connection 
  

   of 
  basalare 
  {Ba) 
  with 
  base 
  of 
  wing; 
  Ba, 
  basalare; 
  C, 
  tergo-sternal 
  

   muscle 
  ("indirect" 
  elevator 
  of 
  the 
  wing); 
  Cx, 
  coxa; 
  Af', 
  coxo-basalar 
  

   muscle 
  (" 
  direct 
  " 
  pronator-extensor 
  of 
  the 
  wing); 
  PI, 
  pleuron; 
  S, 
  ster- 
  

   num; 
  T, 
  tergum; 
  W, 
  wing; 
  WP, 
  pleural 
  wing 
  process 
  

  

  