﻿NUMBER 
  OF 
  HEAD-SEGMENTS 
  IN 
  INSECTS. 
  283 
  

  

  the 
  maggot 
  of 
  the 
  flesh 
  fly, 
  is 
  one 
  of 
  the 
  lowest 
  forms 
  we 
  have 
  yet 
  exam- 
  

   ined, 
  and 
  we 
  have 
  already 
  seen 
  that 
  its 
  head 
  appears 
  to 
  be 
  formed 
  of 
  

   four 
  and 
  perhaps 
  even 
  of 
  five 
  segments. 
  This 
  is 
  the 
  greatest 
  number 
  

   yet 
  noticed 
  in 
  the 
  head 
  of 
  the 
  larva 
  of 
  any 
  species. 
  If, 
  therefore, 
  we 
  can 
  

   trace 
  the 
  like 
  number 
  in 
  the 
  head 
  of 
  a 
  perfect 
  insect, 
  we 
  may 
  fairly 
  con- 
  

   clude 
  that 
  this 
  is 
  the 
  normal 
  number 
  of 
  segments 
  throughout 
  the 
  class. 
  

   The 
  head 
  of 
  the 
  great 
  water-beetle. 
  Hydrous 
  piceus, 
  is 
  remarkably 
  well- 
  

   fitted 
  for 
  exemplifying 
  the 
  number 
  of 
  segments 
  of 
  which 
  the 
  head 
  is 
  

   originally 
  composed, 
  the 
  remains 
  of 
  four 
  of 
  the 
  segments 
  being 
  distinctly 
  

   marked 
  J 
  and 
  it 
  also 
  aflbrds 
  us 
  a 
  proof 
  of 
  the 
  correctness 
  of 
  the 
  opinions 
  

   advanced 
  by 
  Savigny 
  and 
  others, 
  that 
  the 
  organs 
  of 
  manducation 
  are 
  

   the 
  proper 
  articulated 
  members 
  of 
  distinct 
  segments, 
  and 
  are 
  perfectly 
  

   analogous 
  to 
  the 
  proper 
  organs 
  of 
  locomotion. 
  

  

  " 
  We 
  shall 
  first 
  describe 
  the 
  parts 
  of 
  which 
  the 
  head 
  is 
  composed, 
  and 
  

   then 
  endeavor 
  to 
  explain 
  the 
  manner 
  in 
  which 
  these 
  parts 
  have 
  been 
  

   developed 
  from 
  several 
  segments 
  to 
  form 
  the 
  perfect 
  cranium 
  and 
  its 
  

   appendages. 
  It 
  has 
  hitherto 
  been 
  customary 
  with 
  naturalists 
  to 
  desig- 
  

   nate 
  the 
  head 
  the 
  first 
  segment 
  of 
  the 
  body, 
  and 
  as 
  every 
  change 
  in 
  the 
  

   nomenclature 
  of 
  a 
  distinct 
  part 
  ought 
  always 
  to 
  be 
  avoided, 
  unless 
  pos- 
  

   itively 
  required, 
  through 
  fear 
  of 
  creating 
  contusion, 
  we 
  shall 
  not 
  deviate 
  

   on 
  the 
  present 
  occasion 
  from 
  the 
  established 
  mode 
  ; 
  but 
  when 
  speaking 
  

   of 
  it 
  as 
  a 
  whole 
  shall 
  consider 
  it 
  the 
  first 
  segment, 
  while 
  the 
  aggregation 
  

   of 
  segments 
  of 
  which 
  it 
  is 
  composed 
  we 
  shall 
  designate 
  individually 
  suh- 
  

   segments^ 
  distinguishing 
  them 
  numerically 
  in 
  the 
  order 
  in 
  which 
  they 
  

   appear 
  to 
  exist 
  in 
  the 
  earliest 
  condition 
  of 
  the 
  ftetal 
  larva.'^ 
  

  

  If 
  we 
  apply 
  the 
  law 
  enunciated 
  by 
  Savigny, 
  and 
  which 
  holds 
  good 
  as 
  

   a 
  rule 
  throughout 
  the 
  Hexapod 
  Insects, 
  i. 
  e., 
  that 
  each 
  segment 
  of 
  the 
  

   body 
  of 
  insects 
  bears 
  but 
  a 
  single 
  pair 
  of 
  jointed 
  appendages, 
  we 
  find 
  

   that 
  as 
  the 
  head 
  of 
  insects 
  is 
  provided 
  with 
  four 
  pairs 
  of 
  appendages, 
  

   viz., 
  the 
  antennae, 
  mandibles, 
  first 
  maxillae, 
  and 
  labium 
  (or 
  second 
  max- 
  

   illae), 
  there 
  must 
  be 
  four 
  corresponding 
  segments. 
  

  

  While 
  the 
  subject 
  becomes 
  clearer 
  when, 
  with 
  Newport, 
  we 
  examine 
  

   an 
  insect 
  in 
  the 
  larva 
  state, 
  the 
  fact 
  that 
  the 
  head 
  of 
  insects 
  is 
  really 
  

   composed 
  of 
  but 
  four 
  segments 
  becomes 
  readily 
  demonstrated 
  when 
  we 
  

   examine 
  the 
  embryo 
  at 
  an 
  early 
  stage 
  of 
  its 
  existence. 
  In 
  our 
  embryo- 
  

   logical 
  studies 
  on 
  the 
  Thysauurous 
  insects 
  (Isotoma), 
  on 
  Neuropterous 
  

   insects 
  (Diplax), 
  on 
  the 
  beetles 
  and 
  the 
  flea 
  and 
  Hymenoptera 
  {Nematus 
  

   ventricosus)y 
  our 
  attention 
  was 
  specially 
  directed 
  to 
  this 
  point, 
  and 
  it 
  

   appeared 
  very 
  plain 
  and 
  easily 
  demonstrable 
  that 
  the 
  head 
  of 
  winged 
  

   insects 
  of 
  all 
  orders 
  consists 
  of 
  four 
  segments 
  (arthromeres) 
  and 
  no 
  

   more.^^ 
  

  

  An 
  inspection 
  of 
  the 
  figures 
  published 
  by 
  the 
  difierent 
  writers 
  on 
  the 
  

   embryology 
  of 
  insects 
  appears 
  to 
  confirm 
  this 
  view, 
  and 
  in 
  our 
  ^* 
  Guide 
  

  

  136 
  See 
  Embryological 
  Studies 
  on 
  Diplax, 
  Peiitliemis, 
  and 
  the 
  Tliysanurous 
  genus 
  Isotoma, 
  by 
  A. 
  S. 
  

   Packard, 
  jr.; 
  Memoirs 
  Peab. 
  Acad. 
  Sc, 
  Salem, 
  1871, 
  p. 
  21; 
  also 
  Second 
  Memoir, 
  1872. 
  This 
  view 
  was 
  

   stated 
  in 
  the 
  author's--*' 
  Guide 
  to 
  the 
  Study 
  of 
  Insects," 
  second 
  edition. 
  Graber 
  (Die 
  Insekten, 
  Miiu- 
  

   chen, 
  1879, 
  p. 
  430) 
  also 
  states 
  that 
  the 
  head 
  is 
  composed 
  of 
  four 
  segments. 
  

  

  