﻿230 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  optic 
  ganglia 
  were 
  cut 
  through 
  by 
  the 
  microtome, 
  affording 
  instructive 
  

   sections 
  of 
  the 
  three 
  lenticular 
  masses 
  of 
  white 
  unstained 
  granulo-fibrous 
  

   substance 
  surrounded 
  by 
  ganglion 
  cells. 
  

  

  INTERNAL 
  TOPOGRAPHY 
  OF 
  THE 
  BRAIN. 
  

  

  Disregarding 
  the 
  envelope 
  of 
  cortical 
  ganglionic 
  cells, 
  though 
  they 
  are 
  

   evidently 
  of 
  primary 
  importance 
  in 
  the 
  physiology 
  of 
  the 
  insect's 
  brain, 
  

   we 
  will 
  now 
  describe 
  the 
  internal 
  topography 
  of 
  the 
  brain. 
  It 
  consists 
  

   primarily 
  of 
  an 
  irregular 
  net-work 
  of 
  nerve-fibers, 
  inclosing 
  masses 
  of 
  

   granulated 
  nerve 
  matter. 
  This 
  mass 
  is 
  divided 
  into 
  a 
  number 
  of 
  sep- 
  

   arate 
  areas 
  or 
  lobes, 
  of 
  which 
  the 
  u 
  central 
  body" 
  (corpus 
  centrale 
  of 
  

   Flogel 
  and 
  Newton) 
  is 
  single 
  and 
  situated 
  between 
  or 
  in 
  the 
  median 
  line 
  

   of 
  the 
  two 
  hemispheres. 
  There 
  is 
  also 
  a 
  primitive 
  superior 
  and 
  inferior 
  

   central 
  region, 
  better 
  shown, 
  however, 
  in 
  the 
  brain 
  of 
  the 
  embryo 
  and 
  

   larval 
  locust 
  than 
  in 
  the 
  adult. 
  Besides 
  these 
  areas 
  are 
  the 
  rounded 
  

   masses 
  or 
  "lobes," 
  i. 
  e., 
  the 
  optic, 
  antennal, 
  or 
  olfactory 
  and 
  commissural 
  

   lobes 
  5 
  the 
  optic 
  nerves 
  arising 
  from 
  the 
  optic 
  lobes, 
  the 
  antennal 
  nerves 
  

   from 
  the 
  antennal 
  lobes, 
  and 
  the 
  commissures 
  surrounding 
  the 
  oesopha- 
  

   gus 
  and 
  connecting 
  the 
  brain 
  with 
  the 
  subcesophageal 
  ganglion 
  ; 
  these 
  

   arise 
  from 
  the 
  commissural 
  lobes. 
  Finally 
  a 
  "mushroom 
  body' 
  7 
  is 
  

   situated 
  in 
  the 
  upper 
  and 
  central 
  part 
  of 
  each 
  hemisphere. 
  

  

  The 
  central 
  body. 
  — 
  This 
  is 
  the 
  only 
  single 
  or 
  unpaired 
  organ 
  in 
  the 
  

   brain. 
  It 
  is 
  best 
  seen 
  in 
  section 
  17 
  (PI. 
  X, 
  Fig. 
  2), 
  which 
  also 
  passes 
  

   through 
  the 
  optic 
  and 
  antennal 
  lobes 
  and 
  the 
  trabecular 
  and 
  mushroom 
  

   bodies. 
  This 
  singular 
  organ 
  is 
  apparently 
  present 
  in 
  all 
  winged 
  insects, 
  

   though 
  differing 
  somewhat 
  in 
  structure 
  in 
  different 
  insects. 
  It 
  is, 
  as 
  

   seen 
  in 
  PI. 
  X, 
  Fig. 
  2, 
  situated 
  in 
  the 
  same 
  plane 
  as 
  the 
  peduncle 
  and 
  

   in 
  the 
  same 
  plane 
  as 
  the 
  center 
  of 
  the 
  entire 
  mushroom 
  body, 
  and 
  rests 
  

   upon 
  the 
  inner 
  sides 
  of 
  the 
  trabecular. 
  Section 
  16 
  does 
  not 
  pass 
  through 
  

   it, 
  though 
  the 
  next 
  section, 
  which 
  is 
  g-Jo 
  inch 
  thick, 
  passes 
  through 
  its 
  

   middle. 
  Section 
  18 
  (Fig. 
  4) 
  passes 
  through 
  its 
  back, 
  while 
  the 
  next 
  sec- 
  

   tion 
  does 
  not 
  include 
  any 
  part 
  of 
  it 
  ; 
  hence 
  its 
  antero-posterior 
  diameter 
  

   is 
  slightly 
  over 
  -^ 
  of 
  an 
  inch. 
  It 
  is 
  about 
  twice 
  as 
  broad 
  as 
  high, 
  and 
  

   thus 
  is 
  a 
  small 
  body, 
  though 
  from 
  the 
  universality 
  of 
  its 
  occurrence 
  in 
  

   winged 
  insects, 
  it 
  may 
  be 
  one 
  of 
  considerable 
  importance. 
  

  

  It 
  is 
  surrounded 
  by 
  a 
  dense 
  net- 
  work 
  of 
  fibers 
  containing 
  a 
  few 
  small 
  

   ganglionic 
  cells, 
  the 
  fibres 
  in 
  front 
  continuous 
  with 
  those 
  near 
  the 
  bottom 
  

   of 
  the 
  frontal 
  median 
  furrow 
  and 
  connecting 
  the 
  two 
  optic 
  lobes. 
  Pos- 
  

   teriorly 
  the 
  fibers 
  apparently 
  are 
  not 
  continuous 
  with 
  those 
  of 
  the 
  trabe- 
  

   cular; 
  hence 
  the 
  central 
  body 
  appears 
  to 
  be 
  quite 
  isolated 
  from 
  the 
  rest 
  

   of 
  the 
  brain. 
  Its 
  substance, 
  when 
  magnified 
  400 
  diameters, 
  appears 
  to 
  

   be 
  a 
  white 
  granular 
  matter 
  like 
  the 
  adjoining 
  parts 
  of 
  the 
  bran. 
  It 
  is 
  

   divided 
  into 
  two 
  parts, 
  the 
  superior 
  and 
  inferior, 
  the 
  former 
  part 
  con- 
  

   stituting 
  the 
  larger 
  part 
  of 
  the 
  body. 
  The 
  inferior 
  portion 
  is 
  separated 
  

   by 
  fibers 
  from 
  the 
  superior; 
  it 
  contains 
  numerous 
  nucleated 
  spherical 
  

   cells 
  situated 
  either 
  irregularly 
  or 
  perhaps 
  primarily 
  (see 
  PI. 
  XIV, 
  Fig. 
  3, 
  

  

  