﻿NUMBER 
  OF 
  HEAD-SEGMENTS 
  IN 
  INSECTS. 
  285 
  

  

  fourth 
  (labial) 
  segment 
  is 
  quite 
  separate 
  from 
  the 
  rest 
  of 
  the 
  head. 
  

   Fig. 
  11 
  (in 
  text), 
  copied 
  from 
  our 
  Memoir, 
  also 
  m^>»t^ 
  

  

  shows 
  in 
  a 
  saw 
  fly 
  larva 
  (Nematus 
  ventrieosus) 
  the 
  

   relations 
  of 
  the 
  labial 
  or 
  fourth 
  segment 
  to 
  the 
  

   rest 
  of 
  the 
  head. 
  The 
  suture 
  between 
  the 
  labial 
  //■'''"'^^^^y--*^ 
  

   segment 
  and 
  the 
  pre-oral 
  part 
  of 
  the 
  head 
  disap- 
  

   pears 
  in 
  adult 
  life. 
  From 
  this 
  sketch 
  it 
  would 
  

   seem 
  that 
  the 
  back 
  part 
  of 
  the 
  head, 
  i. 
  e., 
  of 
  the 
  ^^ 
  

   epicranium, 
  may 
  be 
  made 
  up 
  in 
  part 
  of 
  the 
  tergite 
  

   or 
  pleurites 
  of 
  the 
  mandibular 
  segment, 
  since 
  the 
  ^^^ 
  ii_Head 
  of 
  embr 
  o 
  

   mandibular 
  muscles 
  are 
  inserted 
  on 
  the 
  roof 
  of 
  the 
  ^"©"latus, 
  showinsj 
  the 
  labiai 
  

  

  segment, 
  occ, 
  lotmiag 
  the 
  occi- 
  

  

  head 
  behind 
  the 
  eyes. 
  It 
  is 
  this 
  segment 
  which 
  put; 
  ci, 
  ciypeus,- 
  i&, 
  labmm; 
  

  

  " 
  " 
  ma, 
  manaiDle; 
  7na?n, 
  muscle 
  of 
  

  

  in 
  Oorydalis 
  evidently 
  forms 
  the 
  occiput, 
  and 
  of 
  same; 
  mx, 
  maxiiia; 
  mx', 
  2d 
  

  

  _.,. 
  , 
  . 
  ,,, 
  ., 
  . 
  maxilla 
  (labium) 
  ; 
  oes, 
  oesopha- 
  

  

  which 
  in 
  most 
  other 
  insects 
  there 
  is 
  no 
  trace 
  m 
  gus. 
  

   larval 
  or 
  adult 
  life. 
  

  

  It 
  appears, 
  then, 
  that 
  the 
  epicranium, 
  or 
  that 
  piece 
  (sclerite) 
  bearing 
  

   the 
  eyes, 
  ocelli, 
  and 
  antennae, 
  and 
  in 
  front 
  the 
  clypeus 
  and 
  labrum, 
  is 
  

   formed 
  from 
  the 
  original 
  procephalic 
  lobes, 
  and. 
  represents 
  the 
  first 
  or 
  

   antennal 
  segment, 
  and 
  is 
  pleural, 
  the 
  clypeus 
  and 
  labrum 
  being 
  the 
  ter- 
  

   gal 
  portion 
  of 
  the 
  segment; 
  while 
  the 
  remainder 
  of 
  the 
  original 
  or 
  primi- 
  

   tive 
  segments 
  are 
  obsolete, 
  except 
  in 
  those 
  insects 
  which 
  retain 
  traces 
  

   of 
  an 
  occiput 
  or 
  fourth 
  cephalic 
  tergite. 
  All 
  of 
  the 
  gular 
  region 
  of 
  the 
  

   head 
  probably 
  represents 
  the 
  base 
  of 
  the 
  primitive 
  second 
  maxillae. 
  

  

  