﻿PLATYPTILIA 
  ISODACTYLUS. 
  191 
  

  

  ends 
  (June 
  17th, 
  1904). 
  Second 
  instar' 
  1 
  ' 
  : 
  The 
  head 
  has 
  increased 
  

   from 
  a 
  width 
  of 
  025mm. 
  to 
  one 
  of 
  nearly 
  0-5mm. 
  (in 
  the 
  third 
  instar 
  

   it 
  is 
  0'15mm., 
  and 
  in 
  the 
  fullgrown 
  larva 
  l*2mm.) 
  ; 
  there 
  are 
  skin- 
  

   points 
  everywhere, 
  colourless 
  and 
  transparent, 
  but 
  very 
  prominent. 
  

   The 
  arrangement 
  of 
  hairs 
  and 
  tubercles 
  seems 
  to 
  be 
  already 
  that 
  of 
  

   the 
  adult 
  larva, 
  viz., 
  6 
  hairs 
  on 
  each 
  side 
  of 
  the 
  prothoracic 
  plate, 
  3 
  set 
  as 
  

   a 
  triangle 
  in 
  front 
  of 
  spiracle, 
  and 
  2, 
  level, 
  at 
  base 
  of 
  legs 
  ; 
  on 
  the 
  2nd 
  

   and 
  3rd 
  thoracic 
  segments 
  there 
  are 
  4 
  pairs 
  of 
  hairs 
  — 
  the 
  first 
  pair, 
  a 
  

   small 
  inner 
  and 
  longer 
  outer, 
  placed 
  slightly 
  trapezoidally 
  ; 
  the 
  second 
  

   pair, 
  a 
  small 
  inner 
  and 
  large 
  outer, 
  slightly 
  reversed 
  trapezoidal 
  (if 
  

   these 
  4 
  hairs 
  were 
  described 
  as 
  actually 
  in 
  line 
  the 
  error 
  would 
  be 
  

   trifling, 
  and 
  if 
  said 
  to 
  be 
  equidistant 
  it 
  would 
  be 
  little 
  more 
  appreciable, 
  

   the 
  distance 
  between 
  the 
  hairs 
  of 
  each 
  pair 
  being 
  more 
  than 
  half 
  that 
  

   between 
  the 
  pairs) 
  ; 
  the 
  third 
  pair 
  is 
  not 
  quite 
  so 
  close, 
  the 
  upper 
  hair 
  

   is 
  small 
  the 
  lower 
  large, 
  the 
  upper 
  one 
  is 
  behind 
  the 
  lower, 
  the 
  line 
  

   joining 
  them 
  being 
  about 
  45° 
  from 
  the 
  horizontal, 
  the 
  upper 
  one 
  is 
  so 
  

   small 
  that 
  it 
  may 
  easily 
  have 
  been 
  present 
  in 
  the 
  first 
  instar 
  and 
  escaped 
  

   observation 
  ; 
  the 
  fourth 
  pair 
  is 
  the 
  pair 
  on 
  a 
  level 
  at 
  base 
  of 
  legs. 
  

   The 
  abdominal 
  tubercles, 
  i, 
  ii 
  and 
  iii 
  are 
  in 
  usual 
  position 
  — 
  i 
  the 
  

   smallest, 
  ii 
  the 
  largest, 
  i 
  and 
  ii 
  are 
  very 
  far 
  apart 
  and 
  very 
  trapezoidal, 
  

   iii 
  being 
  almost 
  as 
  near 
  ii 
  as 
  i 
  is. 
  Tubercle 
  v 
  is 
  small, 
  below 
  spiracle 
  ; 
  

   iv 
  large, 
  lower 
  and 
  behind 
  ; 
  vi 
  is 
  solitary, 
  large, 
  towards 
  hind 
  margin 
  

   of 
  segment 
  ; 
  vii 
  has 
  one 
  hair 
  very 
  large, 
  the 
  two 
  in 
  front 
  of 
  it 
  

   small. 
  There 
  are 
  6 
  hooks 
  to 
  prolegs 
  and 
  5 
  to 
  anal 
  claspers. 
  

   The 
  hairs 
  are 
  all 
  smooth 
  and 
  pointed. 
  Third 
  instar: 
  The 
  same 
  

   description 
  would 
  apply 
  to 
  the 
  third 
  instar, 
  except 
  that 
  there 
  are 
  9 
  

   hooks 
  to 
  the 
  prolegs, 
  and 
  7 
  to 
  the 
  anal 
  claspers, 
  and 
  that 
  the 
  skin- 
  

   points 
  are 
  prolonged 
  into 
  fine 
  needle 
  points. 
  There 
  are 
  still 
  no 
  other 
  

   secondary 
  hairs. 
  Final 
  instar: 
  In 
  the 
  last 
  skin, 
  the 
  skin-points 
  

   are 
  quite 
  rounded, 
  but 
  a 
  certain 
  number 
  have 
  developed 
  into 
  quasi- 
  

   secondary 
  hairs. 
  These 
  are 
  most 
  abundant 
  on 
  the 
  anterior 
  segments 
  ; 
  

   on 
  the 
  mesothorax, 
  they 
  are 
  fairly 
  regularly 
  distributed 
  on 
  the 
  darker 
  

   portions 
  of 
  the 
  middle 
  zone 
  of 
  the 
  segment, 
  but 
  are 
  not 
  difficult 
  to 
  

   count, 
  viz., 
  about 
  37 
  on 
  either 
  side, 
  from 
  dorsal 
  line 
  to 
  leg- 
  base. 
  On 
  

   the 
  abdominal 
  segments, 
  they 
  are 
  wanting 
  in 
  the 
  spiracular 
  region, 
  

   from 
  just 
  above 
  iii 
  to 
  below 
  v; 
  there 
  are 
  about 
  13 
  round 
  i 
  and 
  ii, 
  

   and 
  6 
  between 
  iv-fv 
  and 
  vi, 
  on 
  the 
  1st 
  abdominal, 
  and 
  none 
  below 
  vi. 
  

   On 
  the 
  following 
  segments 
  they 
  occur 
  right 
  down 
  to 
  the 
  ventral 
  line. 
  

   On 
  the 
  5th 
  abdominal 
  there 
  are 
  about 
  25 
  above 
  iii, 
  and 
  about 
  30 
  below 
  

   iv. 
  On 
  the 
  7th 
  abdominal 
  there 
  are 
  14 
  on 
  dorsum 
  (above 
  iii) 
  and 
  

   8 
  below 
  iv. 
  On 
  the 
  8th 
  abdominal 
  there 
  may, 
  or 
  may 
  not. 
  be 
  3 
  or 
  

  

  * 
  The 
  larva 
  in 
  the 
  first 
  instar 
  has 
  apparently 
  no 
  skin-points. 
  I 
  may 
  have 
  

   missed 
  the 
  second 
  instar, 
  and 
  what 
  I 
  take 
  to 
  be 
  the 
  second, 
  may 
  really 
  be 
  the 
  third. 
  

   I 
  think, 
  however, 
  that 
  this 
  is 
  not 
  so. 
  The 
  chief 
  ground 
  for 
  supposing 
  this 
  to 
  be 
  

   the 
  case, 
  is 
  the 
  considerable 
  increase 
  in 
  the 
  size 
  of 
  the 
  head 
  between 
  the 
  first 
  and 
  

   supposed 
  second 
  instar. 
  A 
  very 
  similar 
  amount 
  of 
  increase, 
  however, 
  occurs 
  in 
  

   Adaina 
  microdactyly 
  where 
  I 
  have 
  a 
  larva 
  at 
  moult 
  showing 
  both 
  heads 
  in 
  the 
  

   same 
  specimen, 
  and 
  what 
  is 
  nearer 
  home, 
  a 
  precisely 
  similar 
  increase 
  in 
  the 
  size 
  oi 
  

   the 
  head 
  occurs 
  at 
  the 
  first 
  moult. 
  The 
  difficulty 
  of 
  following 
  one 
  larva 
  in 
  these 
  

   internal 
  feeders 
  is 
  practically 
  too 
  great 
  to 
  be 
  achieved, 
  especially 
  when 
  one 
  has 
  to 
  

   be 
  economical 
  of 
  material, 
  but 
  that 
  o( 
  comparing 
  a 
  number 
  of 
  different 
  specimens 
  

   may 
  usually 
  be 
  depended 
  on, 
  the 
  criteria 
  of 
  different 
  instars 
  being, 
  not 
  the 
  size 
  

   of 
  the 
  larva 
  itself, 
  but 
  of 
  its 
  head, 
  or 
  the 
  Lengths 
  of 
  the 
  hairs, 
  or 
  other 
  hard 
  parts 
  

   that 
  are 
  invariable 
  throughout, 
  an 
  instar 
  (Chapman). 
  

  

  