﻿THE 
  BRAIN 
  OF 
  THE 
  LOCUST. 
  227 
  

  

  A. 
  The 
  large 
  ganglion 
  cells 
  (PL 
  XI, 
  Figs. 
  3, 
  3 
  a, 
  3 
  b, 
  3 
  c, 
  3 
  d, 
  3 
  e) 
  are 
  

   oval, 
  and 
  send 
  off 
  usually 
  a 
  single 
  nerve 
  fiber 
  ; 
  they 
  have 
  a 
  thin 
  fibrous 
  

   cell 
  wall, 
  and 
  the 
  contents 
  are 
  finely 
  granular. 
  The 
  nucleus 
  is 
  very 
  large, 
  

   often 
  one-half 
  the 
  diameter 
  of 
  the 
  entire 
  cell, 
  and 
  is 
  composed 
  of 
  large 
  

   round 
  refractive 
  granules, 
  usually 
  concealing 
  the 
  nucleolus 
  (the 
  granules 
  

   are 
  much 
  larger 
  and 
  fewer 
  in 
  Dumber 
  and 
  the 
  nucleolus 
  is 
  less 
  distinct 
  

   than 
  in 
  the 
  brain 
  of 
  Lunulas, 
  the 
  king 
  crab). 
  These 
  large 
  ganglion 
  cells 
  

   are 
  most 
  abundant 
  and 
  largest 
  on 
  each 
  side 
  of 
  the 
  upper 
  furrow, 
  and 
  in 
  

   front 
  of 
  the 
  "central 
  body," 
  also 
  at 
  the 
  bottom 
  of 
  the 
  lower 
  furrow, 
  

   and 
  along 
  the 
  exterior 
  of 
  the 
  optic 
  and 
  antennal 
  lobes, 
  and 
  along 
  the 
  

   commissural 
  lobes. 
  

  

  B. 
  The 
  small 
  ganglion 
  cells 
  apparently 
  differ 
  chiefly 
  in 
  size 
  from 
  the 
  

   large 
  ones, 
  and 
  are 
  most 
  numerous 
  in 
  the 
  front 
  swelling 
  of 
  each 
  hemi- 
  

   sphere 
  ; 
  they 
  surround 
  and 
  fill 
  the 
  calices 
  of 
  the 
  mushroom 
  bodies, 
  and 
  

   they 
  extend 
  along 
  each 
  optic 
  nerve 
  and 
  form 
  a 
  large 
  proportion 
  of 
  each 
  

   optic 
  ganglion, 
  especially 
  the 
  layer 
  next 
  to 
  the 
  retina 
  of 
  the 
  eye, 
  though 
  

   they 
  are 
  replaced 
  by 
  large 
  ganglion 
  cells 
  at 
  the 
  junction 
  of 
  the 
  fibrous 
  

   part 
  of 
  the 
  optic 
  nerve 
  with 
  the 
  dilated 
  granular 
  portion. 
  The 
  brain 
  

   is 
  surrounded 
  more 
  or 
  less 
  completely 
  by 
  the 
  connective 
  tissue 
  cells 
  

   belonging 
  to 
  the 
  mesoderm 
  or 
  middle 
  germ 
  layer, 
  and 
  which 
  are 
  some- 
  

   times 
  liable 
  to 
  be 
  confounded 
  with 
  the 
  ganglion 
  cells, 
  as 
  they 
  stain 
  the 
  

   same 
  tint 
  with 
  carmine. 
  It 
  should 
  be 
  borne 
  in 
  mind 
  that 
  the 
  nervous 
  

   system, 
  ganglia 
  and 
  nerves, 
  originate 
  from 
  the 
  tegumental 
  or 
  exodermal 
  

   layer. 
  

  

  II. 
  The 
  medullary 
  or 
  inner 
  part 
  of 
  the 
  brain 
  consists 
  of 
  matter 
  which 
  

   remains 
  white 
  or 
  unstained 
  after 
  the 
  preparation 
  has 
  remained 
  thor- 
  

   oughly 
  exposed 
  to 
  the 
  action 
  of 
  the 
  carmine. 
  It 
  consists 
  of 
  minute 
  

   granules 
  and 
  interlacing 
  fibers. 
  The 
  latter 
  often 
  forms 
  a 
  fine 
  irregular 
  

   net- 
  work 
  inclosing 
  masses 
  of 
  finely 
  granulated 
  nerve 
  matter. 
  

  

  In 
  the 
  antennal 
  and 
  commissural 
  lobes 
  is 
  a 
  third 
  kind 
  of 
  matter, 
  in 
  

   addition 
  to 
  the 
  granular 
  and 
  fibrous 
  substances, 
  which 
  forms 
  irregularly 
  

   rounded 
  masses, 
  cream-colored 
  in 
  picro-carmine 
  preparations, 
  and 
  which 
  

   stain 
  dark 
  with 
  osmic 
  acid. 
  This 
  is 
  called 
  by 
  Dietl 
  "markmbstanz," 
  

   and 
  is 
  described 
  by 
  Newton 
  as 
  " 
  a 
  peculiar 
  arrangement 
  of 
  nervous 
  mat- 
  

   ter, 
  which 
  appears 
  sometimes 
  as 
  fine 
  fibrillar, 
  with 
  an 
  axial 
  arrangement, 
  

   sometimes 
  as 
  a 
  very 
  fine 
  net-work 
  of 
  different 
  thicknesses, 
  and 
  some- 
  

   times 
  as 
  thin 
  lamella, 
  or 
  altogether 
  homogeneous. 
  Under 
  all 
  these 
  

   forms 
  this 
  third 
  group 
  of 
  textures 
  is 
  characterized 
  by 
  turning 
  very 
  dark 
  

   under 
  the 
  influence 
  of 
  osmic 
  acid, 
  whilst 
  the 
  other 
  elements 
  are 
  only 
  

   turned 
  brown." 
  

  

  It 
  is 
  to 
  be 
  noticed 
  that 
  this 
  central 
  unstained 
  portion 
  contains 
  few, 
  if 
  

   any, 
  ganglion 
  cells, 
  and 
  it 
  is 
  most 
  probable 
  that 
  the 
  fibers 
  of 
  which 
  it 
  is 
  

   composed 
  originate 
  from 
  the 
  cortical 
  ganglion 
  cells. 
  At 
  one 
  or 
  two 
  

   points 
  at 
  Fig. 
  3, 
  PL 
  XI, 
  I 
  have 
  seen 
  the 
  fibers 
  passing 
  in 
  from 
  ganglion 
  

   cells 
  towards 
  the 
  middle 
  of 
  the 
  brain. 
  In 
  the 
  horseshoe 
  crab 
  (Limulus), 
  

   owing 
  to 
  the 
  simple 
  structure 
  of 
  the 
  brain, 
  it 
  is 
  evident 
  that 
  the 
  optic 
  

  

  