﻿214 
  

  

  R. 
  J. 
  TILL 
  YARD. 
  

  

  little 
  larger 
  than 
  the 
  others 
  ; 
  9th 
  and 
  10th 
  segments 
  smaller, 
  not 
  so 
  clearly 
  separated 
  

   from 
  one 
  another 
  ; 
  apex 
  very 
  hairy. 
  Primary 
  setae 
  as 
  shown 
  in 
  text-fig. 
  2. 
  The 
  

   10th 
  segment 
  ends 
  somewhat 
  conically 
  in 
  a 
  small 
  anal 
  papilla, 
  on 
  which 
  three 
  weakly 
  

   formed 
  triangular 
  flaps 
  conceal 
  a 
  slight 
  depression. 
  Within 
  this, 
  in 
  a 
  carefully 
  

   cleared 
  slide, 
  an 
  exceedingly 
  minute 
  round 
  hole 
  can 
  be 
  seen, 
  which 
  is 
  probably 
  the 
  

   opening 
  of 
  the 
  silk 
  glands, 
  the 
  original 
  anus 
  having 
  been 
  modified 
  for 
  this 
  purpose. 
  

  

  Chaetotaxy 
  : 
  The 
  primary 
  setae 
  of 
  the 
  head, 
  prothorax, 
  and 
  last 
  two 
  segments 
  

   of 
  the 
  abdomen 
  are 
  on 
  different 
  plans 
  from 
  one 
  another 
  and 
  from 
  the 
  rest 
  of 
  the 
  

   segments, 
  and 
  are 
  not 
  here 
  discussed 
  further. 
  Those 
  of 
  the 
  first 
  eight 
  abdominal 
  

   segments, 
  meso- 
  and 
  metathorax 
  are 
  arranged 
  on 
  a 
  closely 
  similar 
  plan, 
  which 
  is 
  

   comparable 
  with 
  that 
  of 
  the 
  primary 
  setae 
  in 
  the 
  larvae 
  of 
  Lepidoptera, 
  as 
  set 
  forth 
  

   by 
  Fracker 
  (1915). 
  This 
  author 
  names 
  the 
  setae 
  by 
  Greek 
  letters. 
  His 
  method 
  will 
  

   be 
  adopted 
  here 
  ; 
  but 
  in 
  order 
  to 
  make 
  the 
  chaetotaxy 
  simpler 
  to 
  understand, 
  I 
  

   shall 
  also 
  arrange 
  the 
  setae 
  in 
  groups 
  to 
  which 
  positional 
  names 
  can 
  be 
  given, 
  on 
  the 
  

   following 
  plan 
  : 
  — 
  

  

  Position. 
  

  

  

  Names. 
  

  

  

  A 
  nterior 
  

  

  Seta. 
  

  

  Posterior 
  Seta 
  

  

  Dorsal 
  

   Latero-dorsal 
  

  

  a 
  (absent) 
  

   V 
  

  

  6 
  

  

  Lateral 
  or 
  Peristigmatic 
  :— 
  

  

  

  

  

  Upper 
  

  

  Lower 
  

  

  Latero-ventral 
  

  

  e 
  

  

  n 
  

  

  V 
  

  

  

  9 
  

   r(j.) 
  

  

  n 
  

  

  Ventral 
  or 
  Coxal 
  : 
  — 
  

  

  

  

  

  Upper 
  

   Lower 
  

  

  T 
  

   CO 
  

  

  

  a 
  

  

  By 
  using 
  this 
  table, 
  each 
  seta 
  receives, 
  besides 
  its 
  Greek 
  name, 
  a 
  positional 
  name 
  

   which 
  may 
  be 
  found 
  more 
  useful, 
  if 
  somewhat 
  longer 
  ; 
  e.g. 
  /? 
  becomes 
  the 
  posterior 
  

   dorsal 
  seta, 
  t] 
  the 
  lower 
  anterior 
  lateral 
  seta, 
  and 
  so 
  on. 
  

  

  Fracker, 
  in 
  his 
  work, 
  indicates 
  twelve 
  primary 
  setae 
  for 
  a 
  typical 
  segment 
  in 
  the 
  

   first 
  instar 
  of 
  the 
  Lepidopterous 
  caterpillar. 
  These 
  are 
  : 
  alpha, 
  beta, 
  gamma, 
  delta, 
  

   epsilon, 
  rho, 
  eta, 
  kappa, 
  pi, 
  nu, 
  tau 
  and 
  sigma. 
  He 
  also 
  indicates 
  three 
  others 
  as 
  

   subprimaries, 
  which 
  are 
  setae 
  arising 
  at 
  the 
  first 
  ecdysis 
  ; 
  they 
  are 
  theta, 
  mu 
  and 
  

   omega. 
  Of 
  the 
  twelve 
  primary 
  setae, 
  only 
  one, 
  alpha, 
  appears 
  to 
  be 
  absent 
  from 
  

   Ithone, 
  while 
  another, 
  tau, 
  only 
  appears 
  on 
  the 
  metathorax. 
  Of 
  the 
  subprimaries, 
  

   theta 
  is 
  never 
  present 
  in 
  Ithone, 
  thus 
  supporting 
  Fracker 
  's 
  contention 
  that 
  its 
  absence 
  

   from 
  the 
  first 
  instar 
  in 
  Hepialidae 
  shows 
  that 
  it 
  is 
  not 
  a 
  true 
  primary 
  seta 
  ; 
  mu 
  is 
  

   present 
  only 
  on 
  the 
  metathorax 
  ; 
  and 
  omega 
  occurs 
  on 
  both 
  metathorax 
  and 
  abdominal 
  

   segments. 
  It 
  would 
  thus 
  appear 
  that 
  omega 
  is 
  really 
  a 
  primary 
  seta 
  for 
  Ithone, 
  

   and 
  takes 
  the 
  place 
  of 
  the 
  more 
  dorsally 
  situated 
  tau, 
  present 
  in 
  the 
  Lepidoptera. 
  

   This 
  could 
  be 
  easily 
  understood 
  if 
  both 
  omega 
  and 
  tau 
  were 
  actually 
  primary 
  setae 
  

   for 
  the 
  ancestral 
  Panorpoid 
  type, 
  the 
  upper 
  seta 
  being 
  suppressed 
  in 
  Ithone, 
  the 
  

   lower 
  in 
  Lepidoptera. 
  The 
  seta 
  which 
  I 
  have 
  called 
  psi 
  appears 
  to 
  have 
  no 
  homologue 
  

   in 
  Lepidoptera. 
  

  

  Text-fig. 
  5 
  shows 
  the 
  chaetotaxy 
  of 
  the 
  metathorax 
  and 
  first 
  two 
  abdominal 
  

   segments 
  of 
  Ithone 
  in 
  diagrammatic 
  form. 
  From 
  the 
  mid-dorsal 
  line 
  to 
  the 
  dotted 
  

   lateral 
  line 
  above 
  pi, 
  the 
  microtrichia 
  are 
  exceedingly 
  abundant, 
  being 
  only 
  absent 
  

   from 
  certain 
  areas 
  around 
  the 
  primary 
  setae 
  which 
  correspond 
  with 
  the 
  hardened 
  

   plates 
  or 
  pinacula 
  of 
  Mecopterous 
  and 
  Lepidopterous 
  larvae, 
  but 
  which, 
  in 
  Ithone, 
  

   are 
  simply 
  clear, 
  unhardened 
  areas. 
  Each 
  primary 
  seta 
  has 
  a 
  small 
  circular 
  area 
  

   surrounding 
  it, 
  except 
  in 
  the 
  case 
  of 
  eta 
  and 
  kappa, 
  around 
  which 
  there 
  is 
  a 
  larger 
  

   pinaculum 
  enclosing 
  both, 
  and 
  represented 
  by 
  a 
  dotted 
  line 
  in 
  text-fig. 
  5. 
  On 
  the 
  

   meso- 
  and 
  metathorax, 
  there 
  is 
  also 
  a 
  much 
  larger 
  pinaculum 
  enclosing 
  gamma, 
  

  

  