﻿224 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  fibers 
  proceed 
  to 
  the 
  facets 
  of 
  the 
  eye. 
  The 
  optic 
  ganglion 
  connects 
  

   with 
  the 
  brain 
  by 
  the 
  large 
  optic 
  nerve. 
  There 
  are, 
  then, 
  two 
  optic 
  

   nerves, 
  besides 
  three 
  slender 
  nerves 
  (ocellar 
  nerves) 
  sent 
  to 
  each 
  of 
  the 
  

   three 
  ocelli 
  or 
  simple 
  eyes 
  ; 
  moreover, 
  a 
  nerve 
  is 
  sent 
  to 
  each 
  of 
  the 
  an- 
  

   tennae 
  and 
  are 
  hence 
  called 
  the 
  antennal 
  nerves. 
  The 
  relations 
  of 
  the 
  

   brain 
  to 
  the 
  head, 
  and 
  to 
  the 
  succeeding 
  ganglion, 
  and 
  the 
  origins 
  of 
  

   the 
  nerves 
  distributed 
  to 
  the 
  eyes, 
  antennae 
  and 
  ocelli, 
  as 
  well 
  as 
  of 
  the 
  

   nerves 
  sent 
  to 
  the 
  jaws, 
  etc., 
  are 
  clearly 
  seen 
  in 
  the 
  figures 
  on 
  Plate 
  

   IX. 
  

  

  On 
  the 
  other 
  hand 
  the 
  mouth 
  parts, 
  i. 
  e., 
  the 
  jaws 
  {mandibles) 
  and 
  ac- 
  

   cessory 
  jaws 
  (first 
  and 
  second 
  maxillce, 
  the 
  latter 
  called 
  the 
  labium 
  or 
  

   under 
  lip) 
  are 
  each 
  supplied 
  by 
  a 
  pair 
  of 
  nerves, 
  called, 
  respectively, 
  the 
  

   mandibular 
  , 
  maxillary, 
  and 
  labial 
  nerves. 
  These 
  three 
  pairs 
  of 
  nerves 
  

   arise 
  from 
  the 
  subcesophageal 
  ganglion. 
  (See 
  PL 
  IX, 
  Fig. 
  2.) 
  

  

  The 
  brain 
  of 
  insects 
  as 
  distinguished 
  from 
  the 
  brain 
  of 
  vertebrates. 
  — 
  The 
  

   "brain" 
  or 
  supracesophageal 
  ganglion 
  is, 
  as 
  we 
  shall 
  see, 
  a 
  much 
  more 
  

   complicated 
  organ 
  than 
  any 
  of 
  the 
  succeeding 
  ganglia, 
  having 
  impor- 
  

   tant 
  parts 
  which 
  are 
  wanting 
  in 
  all 
  the 
  others, 
  hence 
  it 
  is 
  par 
  excellence 
  

   nearer 
  to 
  our 
  idea 
  of 
  a 
  brain 
  than 
  any 
  of 
  the 
  other 
  nervous 
  centers. 
  It 
  

   should 
  be 
  remembered, 
  however, 
  that 
  the 
  word 
  "brain" 
  is 
  applied 
  to 
  

   this 
  compound 
  ganglion 
  simply 
  by 
  courtesy 
  and 
  as 
  a 
  matter 
  of 
  conve- 
  

   nience, 
  as 
  it 
  does 
  not 
  correspond 
  to 
  the 
  brain 
  of 
  a 
  vertebrate 
  animal, 
  the 
  

   brain 
  of 
  the 
  horse 
  or 
  man 
  being 
  composed 
  of 
  several 
  distinct 
  pairs 
  of 
  

   ganglia. 
  Moreover, 
  the 
  brain 
  and 
  nervous 
  cord 
  of 
  the 
  fish 
  or 
  man 
  is 
  

   fundamentally 
  different, 
  or 
  not 
  homologous 
  with 
  that 
  of 
  the 
  lower 
  or 
  

   invertebrate 
  animals, 
  though 
  the 
  nervous 
  system 
  of 
  the 
  insects 
  and 
  

   Crustacea 
  present 
  greater 
  analogies 
  to 
  that 
  of 
  the 
  vertebrates 
  than 
  any 
  

   other 
  of 
  the 
  lower 
  animals, 
  with 
  the 
  exception, 
  perhaps, 
  of 
  the 
  cuttle- 
  

   fish. 
  The 
  nervous 
  cord 
  of 
  the 
  insect 
  consists 
  of 
  a 
  chain 
  of 
  ganglia 
  con- 
  

   nected 
  by 
  nerves 
  or 
  commissures, 
  while 
  the 
  spinal 
  cord 
  of 
  the 
  fish 
  or 
  

   man 
  is 
  essentially 
  "a 
  double 
  and 
  fused 
  series 
  of 
  nerve-centers." 
  More- 
  

   over, 
  if 
  this 
  cord 
  is 
  cut 
  through, 
  a 
  section 
  shows 
  that 
  it 
  consists 
  of 
  two 
  

   kinds 
  of 
  substances 
  or 
  tissues, 
  called 
  the 
  "gray" 
  and 
  "white" 
  substance. 
  

   The 
  gray 
  matter 
  is 
  situated 
  in 
  the 
  center, 
  and 
  consists 
  largely 
  of 
  nerve 
  

   or 
  so-called 
  " 
  ganglion 
  cells," 
  while 
  the 
  external 
  white 
  matter 
  of 
  the 
  

   brain 
  or 
  cord 
  is 
  composed 
  of 
  a 
  mass 
  of 
  nerve 
  fibers. 
  Now, 
  in 
  the 
  nervous 
  

   system 
  of 
  insects 
  there 
  is 
  nothing 
  to 
  compare 
  with 
  these 
  substances, 
  but 
  

   the 
  ganglia, 
  on 
  the 
  contrary, 
  as 
  we 
  shall 
  see 
  farther 
  on, 
  consist 
  primarily 
  

   of 
  an 
  external 
  layer 
  of 
  ganglion 
  cells, 
  whose 
  fibers 
  pass 
  in 
  to 
  form 
  a 
  

   central 
  fibrous 
  mass 
  or 
  net-work, 
  the 
  meshes 
  of 
  which 
  are 
  filled 
  with 
  a 
  

   fine 
  'granulated 
  nerve 
  substance, 
  the 
  nature 
  of 
  which 
  is 
  not 
  clearly 
  

   understood. 
  Moreover, 
  the 
  entire 
  brain 
  of 
  an 
  insect 
  is 
  white, 
  as 
  are 
  all 
  

   the 
  ganglia. 
  

  

  A 
  ganglion 
  in 
  its 
  simplest 
  form 
  is 
  a 
  little 
  rounded 
  mass, 
  or 
  nodule, 
  of 
  

   ganglion 
  cells, 
  with 
  fibers 
  leading 
  from 
  them 
  5 
  such 
  cells 
  are 
  represented 
  

   by 
  Fig. 
  3 
  a, 
  on 
  Plate 
  XI. 
  Now 
  when 
  the 
  fibers 
  lead 
  in 
  from 
  the 
  sensitive 
  

  

  