﻿THE 
  LARVA 
  AND 
  PUPA 
  OF 
  ORTHOPODOMYIA 
  ARBORICOLLIS. 
  451 
  

  

  Larvae 
  of 
  the 
  genus 
  Orthopodomyia 
  at 
  the 
  fourth 
  instar 
  have 
  been 
  characterised 
  

   among 
  other 
  features 
  as 
  being 
  of 
  a 
  reddish 
  colour. 
  This 
  we 
  found 
  to 
  be 
  true 
  for 
  some 
  

   arboricollis 
  larvae 
  — 
  particularly 
  in 
  the 
  third 
  instar, 
  but 
  often 
  those 
  at 
  the 
  fourth 
  

   instar 
  were 
  either 
  practically 
  colourless 
  or 
  as 
  frequently 
  blue-grey 
  or 
  even 
  sky-blue. 
  

   Another 
  generic 
  character 
  of 
  Orthopodomyia 
  is 
  the 
  development 
  at 
  the 
  fourth 
  instar 
  

   of 
  chitinous 
  plates 
  on 
  the 
  6th-8th 
  abdominal 
  segments. 
  In 
  this 
  character 
  also 
  many 
  

   of 
  our 
  larvae 
  failed 
  ; 
  some 
  of 
  the 
  larvae 
  developing 
  plates 
  on 
  the 
  6th, 
  7th, 
  and 
  8th 
  

   abdominal 
  segments 
  ; 
  others 
  developing 
  any 
  one, 
  or 
  combination 
  of 
  two, 
  of 
  the 
  

   plates 
  only 
  ; 
  while 
  still 
  others 
  failed 
  to 
  develop 
  any 
  sign 
  of 
  a 
  plate, 
  and 
  yet 
  all 
  pupated 
  

   and 
  emerged 
  as 
  perfectly 
  normal 
  adults 
  with 
  no 
  apparent 
  individual 
  differences. 
  

   The 
  chitinous 
  abdominal 
  plates 
  are 
  clearly, 
  in 
  arboricollis 
  at 
  least, 
  an 
  exceedingly 
  

   variable 
  character. 
  

  

  Nor 
  is 
  this 
  the 
  only 
  character 
  in 
  which 
  the 
  larvae 
  of 
  arboricollis 
  show 
  astonishing 
  

   variation. 
  In 
  those 
  collected 
  from 
  the 
  mango 
  tree-hole 
  we 
  noticed 
  with 
  the 
  naked 
  

   eye 
  that 
  there 
  seemed 
  to 
  be 
  present 
  two 
  such 
  easily 
  recognisable 
  types 
  that 
  we 
  felt 
  

   almost 
  certain 
  two 
  distinct 
  species 
  were 
  associated. 
  The 
  one 
  type 
  had 
  short, 
  straight 
  

   antennae, 
  with 
  slender 
  frontal 
  plumes, 
  while 
  the 
  other 
  had 
  long, 
  inwardly 
  curved 
  

   antennae 
  and 
  dense 
  frontal 
  plumes 
  (Plate 
  xxiii, 
  figs. 
  2, 
  3). 
  

  

  When 
  the 
  larvae 
  were 
  examined 
  carefully 
  under 
  the 
  microscope, 
  it 
  was 
  discovered 
  

   that 
  from 
  one 
  extreme 
  to 
  the 
  other 
  there 
  were 
  individuals 
  presenting 
  every 
  inter- 
  

   mediate 
  variation. 
  The 
  larvae 
  were 
  separated 
  into 
  different 
  tubes 
  so 
  that 
  the 
  

   variation 
  in 
  the 
  frontal 
  hairs 
  would 
  form 
  a 
  progressive 
  series 
  from 
  the 
  simplest 
  type 
  

   to 
  the 
  most 
  densely 
  plumose 
  type. 
  This 
  was 
  done 
  with 
  the 
  object 
  of 
  demonstrating 
  

   the 
  points 
  at 
  which 
  possible 
  variations 
  in 
  the 
  adults 
  would 
  appear. 
  Every 
  larva 
  in 
  

   the 
  series, 
  showing 
  also 
  all 
  stages 
  of 
  abdominal-plate 
  development, 
  pupated 
  and 
  

   emerged 
  successfully, 
  but 
  prolonged 
  microscopical 
  comparison 
  failed 
  to 
  show 
  a 
  

   single 
  distinction 
  in 
  the 
  adults, 
  either 
  male 
  or 
  female. 
  The 
  whole 
  of 
  this 
  series 
  has 
  

   been 
  mounted 
  and 
  preserved. 
  

  

  The 
  larvae 
  to 
  the 
  naked 
  eye 
  are 
  unusually 
  hairy, 
  and 
  this 
  condition 
  gives 
  to 
  the 
  

   thorax 
  a 
  characteristic 
  appearance 
  of 
  being 
  greatly 
  widened. 
  The 
  larvae 
  swim 
  

   normally 
  with 
  a 
  slow 
  action 
  of 
  the 
  abdomen, 
  but 
  when 
  disturbed 
  they 
  are 
  capable 
  

   of 
  rapid 
  movement, 
  diving 
  to 
  the 
  bottom 
  and 
  remaining 
  submerged 
  for 
  long 
  periods. 
  

   The 
  specific 
  gravity 
  of 
  the 
  larvae 
  is 
  very 
  nearly 
  the 
  same 
  as 
  that 
  of 
  water, 
  and 
  the 
  

   larvae 
  may 
  often 
  be 
  seen 
  in 
  stable 
  equilibrium 
  at 
  different 
  depths 
  in 
  the 
  water. 
  

  

  Descriptions 
  of 
  the 
  Early 
  Stages. 
  

  

  Larva 
  in 
  the 
  Fourth 
  Instar. 
  

  

  Antennae 
  of 
  two 
  forms 
  : 
  (1) 
  straight 
  and 
  short, 
  or 
  (2) 
  longer, 
  curving 
  downwards 
  

   and 
  inwards 
  towards 
  the 
  apex 
  (Plate 
  xxiii, 
  figs. 
  2, 
  3) 
  ; 
  both 
  forms 
  yellow 
  in 
  colour, 
  

   with 
  a 
  small 
  plume 
  situated 
  at 
  a 
  point 
  about 
  one-third 
  from 
  the 
  base. 
  Frontal 
  

   hairs 
  : 
  eight 
  frontal 
  hairs 
  carried 
  on 
  the 
  anterior 
  periphery 
  of 
  the 
  head 
  between 
  the 
  

   antennae. 
  The 
  plumes 
  are 
  exceedingly 
  variable, 
  sometimes 
  being 
  dense, 
  with 
  widely 
  

   spreading 
  branches, 
  the 
  tips 
  of 
  which 
  curve 
  gracefully 
  upwards 
  ; 
  or 
  these 
  plumes 
  

   only 
  represented 
  by 
  simple, 
  bifurcated, 
  or 
  sparsely 
  branched 
  hairs 
  (Plate 
  xxiii, 
  

   figs. 
  2, 
  3). 
  All 
  intermediate 
  variations 
  between 
  the 
  two 
  extremes 
  occur, 
  often 
  in 
  

   larvae 
  from 
  the 
  same 
  breeding- 
  place. 
  The 
  pair 
  of 
  plumes 
  nearest 
  the 
  middle 
  line 
  

   of 
  the 
  head 
  are 
  much 
  smaller, 
  and 
  are 
  placed 
  a 
  little 
  in 
  front 
  of 
  the 
  others. 
  Situated 
  

   below 
  each 
  eye 
  is 
  a 
  large 
  downwardly 
  directed 
  plume. 
  Eyes 
  small 
  and 
  spherical. 
  

   Head 
  sub-globular, 
  transparent, 
  and 
  from 
  a 
  point 
  at 
  the 
  base 
  of 
  the 
  antennae 
  on 
  the 
  

   dorsal 
  surface 
  a 
  dark 
  line 
  extends 
  backwards 
  enclosing 
  the 
  occipital 
  area 
  in 
  the 
  form 
  

   of 
  an 
  open 
  V- 
  Between 
  the 
  arms 
  of 
  the 
  V 
  at 
  about 
  the 
  centre 
  of 
  the 
  head 
  often 
  an 
  

   oval 
  brown 
  mark 
  occurs. 
  A 
  few 
  scattered 
  simple 
  hairs 
  are 
  present 
  at 
  other 
  points 
  on 
  the 
  

   head. 
  Thorax 
  ornamented 
  at 
  the 
  sides 
  with 
  numerous 
  long 
  hairs 
  bunched 
  together. 
  

   Dorsal 
  surface 
  ornamented 
  with 
  stellate 
  spine 
  hairs 
  like 
  those 
  of 
  Finlaya 
  genicalata, 
  

   and 
  a 
  few 
  long 
  simple 
  hairs. 
  Number 
  of 
  hairs 
  in 
  stellate 
  spine 
  very 
  variable. 
  Abdomen 
  

   (Plate 
  xxiii, 
  figs. 
  1, 
  4) 
  ornamented 
  with 
  stellate 
  spine 
  hairs 
  laterally 
  and 
  dorsally, 
  

  

  