﻿WAGNER 
  ON 
  THE 
  HESc:5IAN 
  FLY. 
  [11] 
  

  

  well* 
  as 
  diligent 
  investigations 
  of 
  the 
  hitherto 
  so 
  much 
  neglected 
  natural 
  

   history 
  of 
  the 
  gall-gnats, 
  of 
  having 
  built 
  a 
  solid 
  foundation 
  and 
  having 
  

   produced 
  rich 
  material 
  for 
  the 
  preparation 
  of 
  an 
  extensiv^e 
  monograph 
  of 
  

   this 
  rather 
  diificult 
  branch 
  of 
  entomology. 
  Dr. 
  Loew, 
  in 
  his 
  monograi:)h 
  

   of 
  the 
  gall-gnats, 
  accepts 
  nine 
  abdominal 
  segments, 
  but 
  does 
  not 
  state 
  

   their 
  number 
  in 
  his 
  later 
  description 
  of 
  the 
  rye 
  gall-gnat 
  {Cecidomyia 
  seca- 
  

   Una). 
  J. 
  Winnertz, 
  on 
  the 
  other 
  hand, 
  in 
  his 
  paper, 
  which 
  closely 
  sup- 
  

   plements 
  and 
  follows 
  the 
  one 
  just 
  mentioned, 
  includes 
  in 
  the 
  genitals 
  the 
  

   organ 
  seen 
  by 
  Loew 
  as 
  the 
  ninth 
  abdominal 
  segment, 
  deciding 
  accord- 
  

   ingly, 
  as 
  previously 
  done 
  by 
  Meigen, 
  for 
  the 
  acceptance 
  of 
  but 
  eight 
  

   abdominal 
  segments. 
  I 
  consider 
  Loew's 
  as 
  the 
  correct 
  view. 
  For 
  the 
  

   sake 
  of 
  brevity 
  I 
  confine 
  myself 
  to 
  our 
  gall-gnat 
  only. 
  Concerning 
  the 
  

   male 
  (Fig. 
  17), 
  the 
  genital 
  orifice 
  lies 
  underneath 
  the 
  papillae 
  subse- 
  

   quently 
  to 
  be 
  described, 
  at 
  the 
  end 
  of 
  a 
  thin, 
  retractile 
  cone, 
  which 
  

   should 
  be 
  taken 
  for 
  the 
  cirrus. 
  This 
  unpaired 
  organ 
  is 
  by 
  no 
  means 
  on 
  

   the 
  clasper, 
  but, 
  as 
  in 
  all 
  gall-gnats 
  examined 
  by 
  me, 
  at 
  the 
  base 
  of 
  the 
  

   clasper 
  itself, 
  from 
  which 
  it 
  follows 
  that 
  the 
  clasper 
  is 
  no 
  appendage, 
  

   and 
  must 
  be 
  taken, 
  regardless 
  of 
  its 
  small 
  size, 
  as 
  an 
  independent 
  seg- 
  

   ment. 
  On 
  the 
  abdomen 
  of 
  a 
  female 
  gall-gnat 
  we 
  can 
  in 
  all 
  cases 
  readily 
  

   distinguish 
  seven 
  abdominal 
  segments. 
  The 
  part 
  following 
  the 
  pygi- 
  

   dium 
  is, 
  in 
  the 
  different 
  species, 
  in 
  shape 
  and 
  consistence 
  of 
  various 
  

   formation, 
  with 
  peculiar 
  pilosity 
  ; 
  but 
  this 
  pygidium 
  allows 
  us 
  in 
  all 
  

   cases 
  to 
  distinguish 
  two 
  segments 
  separated 
  by 
  a 
  transverse 
  fold. 
  In 
  

   the 
  female 
  of 
  our 
  gall-gnat 
  (Figs. 
  20, 
  21, 
  22) 
  the 
  foj-emost 
  of 
  these 
  seg- 
  

   ments 
  is 
  more 
  chitinized; 
  the 
  posterior, 
  yellow 
  segment, 
  placed 
  some- 
  

   what 
  transversely 
  toward 
  the 
  preceding, 
  is 
  membranous, 
  elastic, 
  and 
  

   thereby 
  capable 
  of 
  assuming 
  various 
  forms. 
  According 
  as 
  the 
  ovipositor 
  

   is 
  more 
  or 
  less 
  protruded 
  the 
  membranous 
  organ 
  expands 
  longitudinally 
  

   or 
  it 
  contracts, 
  but 
  it 
  is 
  never 
  actually 
  withdrawn 
  as 
  in 
  the 
  ovipositor. 
  It 
  

   therefore 
  cannot 
  be 
  regarded 
  as 
  a 
  genital 
  organ. 
  Its 
  analogy 
  with 
  the 
  

   last 
  abdominal 
  segments 
  of 
  many 
  other 
  insects, 
  the 
  pygidium 
  especially 
  

   is 
  seen 
  in 
  that 
  it 
  likewise 
  serves 
  for 
  the 
  reception 
  of 
  the 
  ovipositor. 
  If 
  we 
  

   nevertheless 
  reckon 
  it 
  with 
  the 
  genitals 
  we 
  should 
  have 
  to 
  accept 
  in 
  the 
  

   species 
  with 
  a 
  very 
  tapering, 
  cylindrical, 
  and 
  throughout 
  membranous 
  

   pygidium 
  not 
  eigh 
  t 
  but 
  only 
  seven 
  abdominal 
  rings. 
  In 
  a 
  female 
  which, 
  

   in 
  .expiring 
  under 
  the 
  microscope, 
  evacuated 
  a 
  white 
  fluid, 
  I 
  believe 
  I 
  

   have 
  convinced 
  myself 
  that 
  the 
  location 
  of 
  the 
  anal 
  orifice 
  is 
  really 
  be- 
  

   low 
  the 
  posterior 
  end 
  of 
  said 
  organ. 
  Should 
  others 
  make 
  the 
  same 
  

   •observation, 
  the 
  term 
  pygidium 
  would 
  not 
  only 
  agree, 
  but 
  the 
  accepta- 
  

   tion 
  of 
  nine 
  abdominal 
  segments 
  for 
  the 
  female 
  gall-gnat 
  would 
  alto- 
  

   gether 
  irrefutably 
  receive 
  its 
  justification. 
  

  

  In 
  determining 
  the 
  color 
  of 
  the 
  various 
  body-parts 
  I 
  was 
  led 
  by 
  the 
  

   following 
  thought. 
  Tlie 
  smallness 
  of 
  the 
  object 
  is 
  to 
  the 
  naked 
  eye 
  very 
  

   often 
  a 
  hindrance 
  in 
  exactly 
  determining 
  the 
  true 
  color, 
  especiall}' 
  when 
  

   this 
  is 
  not 
  a 
  vivid 
  one. 
  This 
  case 
  appears 
  when 
  we 
  are 
  prevented 
  by 
  

   the 
  deviating 
  color 
  of 
  the 
  pilosity 
  from 
  properly 
  distinguishing 
  the 
  

   parts 
  underneath. 
  Only 
  with 
  the 
  microscope 
  can 
  we 
  get 
  over 
  this 
  diffi- 
  

   culty. 
  Under 
  it 
  the 
  hair-covering, 
  i^reviously 
  appearing 
  uniform, 
  dis- 
  

   solves 
  into 
  single 
  hairs, 
  whose 
  color 
  we 
  can 
  easily 
  distinguish 
  from 
  that 
  

   of 
  the 
  body. 
  Our 
  judgment 
  as 
  to 
  the 
  color 
  of 
  a 
  small, 
  pilose 
  part 
  of 
  an 
  

   insect, 
  therefore, 
  will 
  turn 
  out 
  variously, 
  according 
  to 
  whether 
  we 
  sepa- 
  

   rate 
  the 
  color 
  of 
  the 
  hair 
  from 
  that 
  of 
  the 
  part 
  itself, 
  or 
  whether 
  we 
  con- 
  

   sider 
  the 
  former 
  together 
  with 
  the 
  latter. 
  This 
  is 
  often 
  very 
  important 
  

   in 
  microscopical 
  observations, 
  and 
  must 
  especially 
  in 
  the 
  present 
  case 
  

   be 
  contemplated. 
  The 
  legs 
  of 
  our 
  female 
  gall-gnat, 
  for 
  instance, 
  appear 
  

   to 
  the 
  naked 
  eye 
  as 
  blackish, 
  or 
  black, 
  on 
  account 
  of 
  the 
  pilosity, 
  while 
  

  

  