﻿212 
  

  

  R. 
  J. 
  TILL 
  YARD. 
  

  

  the 
  maxilla, 
  or 
  rather 
  its 
  galea 
  (the 
  palp 
  and 
  lacinia 
  being 
  absent) 
  becoming 
  an 
  elon- 
  

   gated 
  lancet 
  which 
  slides 
  to 
  and 
  fro 
  beneath 
  the 
  somewhat 
  more 
  strongly 
  built 
  spear- 
  

   like 
  mandible 
  ; 
  the 
  upper 
  surface 
  of 
  the 
  maxilla 
  and 
  the 
  lower 
  surface 
  of 
  the 
  mandible 
  

   are 
  grooved, 
  so 
  that 
  a 
  complete 
  tube 
  is 
  formed 
  between 
  them, 
  and 
  along 
  this 
  tube 
  

   the 
  juices 
  of 
  the 
  victim 
  are 
  sucked 
  by 
  pharyngeal 
  action. 
  But 
  in 
  the 
  larva 
  of 
  Ithone, 
  

  

  Fig. 
  3. 
  Ithone 
  fusca, 
  Newm., 
  first 
  larval 
  instar 
  : 
  a, 
  left 
  mandible 
  

   and 
  antenna 
  ; 
  b, 
  left 
  maxilla, 
  with 
  the 
  position 
  of 
  the 
  mandible 
  

   dotted 
  in 
  (x 
  180). 
  

  

  probably 
  owing 
  to 
  the 
  peculiar 
  habit 
  of 
  always 
  striking 
  upwards 
  at 
  its 
  victims, 
  the 
  

   functions 
  of 
  mandible 
  and 
  maxilla 
  appear 
  to 
  be 
  almost 
  reversed, 
  and 
  their 
  structure 
  

   completely 
  so. 
  On 
  first 
  examining 
  one 
  of 
  these 
  larvae, 
  one 
  is 
  struck 
  by 
  the 
  fact 
  

   that 
  it 
  is 
  the 
  lower 
  jaw 
  which 
  is 
  strongly 
  chitinised, 
  and 
  which 
  carries, 
  on 
  its 
  upper 
  

   surface, 
  a 
  deep 
  groove 
  in 
  which 
  the 
  exceedinglv 
  slender 
  apical 
  part 
  of 
  the 
  upper 
  jaw 
  

   works 
  to 
  and 
  fro. 
  The 
  muscles 
  of 
  the 
  mandible 
  are 
  weakly 
  formed, 
  and 
  there 
  is 
  

   little 
  sign 
  left 
  of 
  the 
  original 
  ginglvmus 
  joint 
  connecting 
  it 
  with 
  the 
  head 
  ; 
  on 
  the 
  

   other 
  hand, 
  the 
  sides 
  of 
  the 
  head 
  below 
  the 
  bases 
  of 
  the 
  maxillae 
  are 
  swollen 
  out, 
  

   and 
  even 
  become 
  corrugated 
  in 
  the 
  last 
  instar, 
  to 
  accommodate 
  the 
  powerful 
  muscles 
  

   which 
  work 
  the 
  maxillae 
  themselves. 
  It 
  seemed 
  to 
  me 
  at 
  first 
  probable 
  that 
  mandibles 
  

   and 
  maxillae 
  had 
  indeed 
  changed 
  places 
  through 
  some 
  strange 
  new 
  conformation 
  

   of 
  the 
  head 
  ; 
  but 
  a 
  number 
  of 
  careful 
  dissections 
  show 
  that 
  this 
  is 
  not 
  so, 
  for 
  the 
  

   mandibles 
  can 
  be 
  clearly 
  seen 
  to 
  be 
  attached 
  in 
  their 
  proper 
  places 
  close 
  to 
  and 
  below 
  

   the 
  bases 
  of 
  the 
  antennae, 
  while 
  the 
  maxillae 
  are 
  always 
  closely 
  associated 
  with 
  the 
  

   labium. 
  Text-fig. 
  36 
  shows 
  the 
  slender 
  mandible 
  in 
  situ 
  in 
  the 
  groove 
  of 
  the 
  stoutly 
  

   built 
  and 
  strongly 
  chitinised 
  maxilla 
  below 
  it. 
  The 
  mandible 
  itself 
  (text-fig. 
  3a) 
  

   is 
  attached 
  to 
  the 
  head 
  by 
  a 
  very 
  broad 
  leaf-like 
  base, 
  and 
  is 
  somewhat 
  triangular 
  

   in 
  shape 
  ; 
  the 
  distal 
  half 
  is 
  excessively 
  slender, 
  with 
  the 
  sharply 
  pointed 
  apex 
  curving 
  

   slightly 
  inwards. 
  A 
  narrow 
  groove 
  runs 
  from 
  apex 
  to 
  base, 
  on 
  the 
  underside. 
  It 
  

   is 
  only 
  heavily 
  chitinised 
  towards 
  the 
  apex 
  and 
  along 
  the 
  distal 
  part 
  of 
  the 
  two 
  edges. 
  

   The 
  maxilla 
  (text-fig. 
  3b) 
  consists 
  of 
  a 
  single 
  strongly 
  chitinised 
  piece, 
  probably 
  the 
  

   galea, 
  inserted 
  on 
  a 
  fairly 
  broad 
  base, 
  which 
  appears 
  to 
  represent 
  the 
  stipes 
  and 
  cardo 
  

  

  