﻿286 
  PEOCEEDINGS 
  OF 
  THE 
  FOURTH 
  ENTOMOLOGICAJ. 
  MEETING 
  

  

  of 
  a 
  rapid 
  up-and-down 
  motion 
  of 
  the 
  body, 
  a 
  sort 
  of 
  tetanic 
  vibration. 
  

   This 
  was 
  so 
  rapid 
  that 
  the 
  insect 
  when 
  viewed 
  sideways 
  was 
  difficult 
  

   to 
  see 
  at 
  all, 
  the 
  tarsi 
  being 
  the 
  only 
  parts 
  which 
  could 
  be 
  definitely 
  

   located. 
  On 
  the 
  other 
  hand 
  when 
  it 
  was 
  viewed 
  directly 
  from 
  above 
  

   the 
  degree 
  of 
  concealment 
  was 
  small, 
  merely 
  a 
  slight 
  blurring 
  of 
  the 
  

   outline 
  of 
  the 
  body 
  and 
  femoral 
  portions 
  of 
  the 
  legs. 
  It 
  is 
  probable 
  

   that 
  the 
  fly 
  is 
  thus 
  well 
  concealed 
  from 
  enemies 
  approaching 
  on 
  its 
  

   own 
  level 
  ; 
  those 
  walking 
  on 
  the 
  tree-trunk 
  on 
  which 
  it 
  sits, 
  for 
  example. 
  

   An 
  enemy 
  such 
  as 
  a 
  bird 
  approaching 
  from 
  directly 
  above 
  the 
  insect 
  

   will 
  probably 
  not 
  be 
  misled 
  to 
  any 
  great 
  extent, 
  however, 
  and 
  in 
  this 
  

   respect 
  the 
  device 
  is 
  incomplete. 
  

  

  About 
  a 
  week 
  later 
  it 
  was 
  my 
  good 
  fortune 
  to 
  see 
  the 
  second 
  Tipulid, 
  

   and 
  in 
  this 
  the 
  defect 
  just 
  mentioned 
  was 
  remedied 
  in 
  a 
  very 
  simple 
  

   and 
  effective 
  way. 
  The 
  body 
  was 
  not 
  moved 
  vertically 
  up 
  and 
  down, 
  

   but 
  with 
  a 
  circular 
  motion 
  in 
  a 
  plane 
  at 
  right 
  angles 
  to 
  its 
  long 
  axis 
  

   so 
  that 
  a 
  line 
  from 
  head 
  to 
  tail 
  traced 
  out 
  a 
  cylinder 
  in 
  the 
  air. 
  This 
  

   rotary 
  movement 
  obscures 
  the 
  outline 
  and 
  position 
  of 
  the 
  body 
  when 
  

   seen 
  at 
  any 
  angle. 
  The 
  direction 
  of 
  rotation 
  seemed 
  not 
  always 
  to 
  be 
  

   the 
  same, 
  but 
  of 
  this 
  I 
  was 
  not 
  certain 
  as 
  the 
  motion 
  is 
  confusing. 
  As 
  

   in 
  the 
  former 
  case 
  the 
  fly 
  started 
  its 
  rotation 
  when 
  disturbed. 
  When 
  

   more 
  disturbed, 
  both 
  of 
  them 
  resorted 
  to 
  flight. 
  It 
  seems 
  to 
  me 
  that 
  

   these 
  movements 
  and 
  those 
  of 
  web-shaking 
  spiders 
  are 
  in 
  the 
  same 
  

   category, 
  both 
  consisting 
  of 
  a 
  vibration 
  of 
  the 
  body 
  in 
  the 
  middle 
  of 
  an 
  

   elastic 
  frame-work 
  supplied 
  in 
  the 
  one 
  case 
  by 
  the 
  web 
  and 
  in 
  the 
  other 
  

   by 
  the 
  long 
  thin 
  legs. 
  For 
  a 
  short-legged 
  fly 
  such 
  as 
  the 
  Platypezid 
  

   the 
  amplitude 
  of 
  the 
  body- 
  vibrations 
  obtainable 
  by 
  this 
  method 
  would 
  

   be 
  so 
  small 
  as 
  to 
  be 
  quite 
  useless 
  for 
  effective 
  obliteration 
  or 
  the 
  confu- 
  

   sion 
  of 
  enemies, 
  and 
  the 
  rapidly-alternating 
  translatory 
  motion 
  of 
  the 
  

   whole 
  insect 
  (quite 
  distinct 
  from 
  " 
  running 
  away 
  " 
  in 
  the 
  ordinary 
  

   sense) 
  may 
  be 
  regarded 
  as 
  another 
  means 
  of 
  attaining 
  a 
  similar 
  end. 
  

  

  Mr. 
  Fletcher. 
  

   Mr. 
  White. 
  

   Dr. 
  Gravely. 
  

  

  Mr. 
  V/liite. 
  

  

  You 
  see 
  the 
  same 
  swaying 
  movements 
  in 
  Gongylus 
  and 
  other 
  pre- 
  

   daceous 
  animals. 
  

  

  I 
  do 
  not 
  know 
  what 
  the 
  food 
  of 
  Platypezid 
  imagines 
  may 
  be, 
  but 
  I 
  

   do 
  not 
  think 
  they 
  are 
  predaceous. 
  

  

  In 
  the 
  case 
  of 
  Phalangid 
  spiders 
  and 
  Tipulida) 
  the 
  vibratory 
  move- 
  

   ment 
  renders 
  the 
  animal 
  more 
  difficult 
  to 
  see. 
  Do 
  you 
  think 
  that 
  this 
  

   is 
  so 
  in 
  this 
  case 
  ? 
  

  

  Mr. 
  Howlett 
  thought 
  the 
  motion 
  was 
  protective, 
  rendering 
  their 
  

   capture 
  more 
  difficult 
  than 
  when 
  at 
  rest 
  or 
  on 
  the 
  wing. 
  

  

  