﻿226 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  the 
  larva 
  and 
  pupal 
  stages 
  before 
  attaining 
  the 
  fully 
  developed 
  structure 
  

   of 
  the 
  adult 
  locust. 
  

  

  THE 
  BRAIN 
  OF 
  THE 
  ADULT 
  LOCUST. 
  

  

  The 
  method 
  of 
  examination 
  employed 
  by 
  us 
  has 
  been 
  to 
  cut 
  the 
  brain 
  

   into 
  a 
  number 
  of 
  thin 
  sections 
  by 
  means 
  of 
  the 
  microtome, 
  previously 
  

   hardening 
  the 
  tissues 
  in 
  alcohol. 
  The 
  labor 
  of 
  cutting 
  these 
  sections 
  

   has 
  been 
  performed 
  by 
  Mr. 
  Norman 
  N". 
  Mason, 
  of 
  Providence, 
  E. 
  L, 
  who 
  

   has 
  brought 
  to 
  his 
  work 
  an 
  unusual 
  degree 
  of 
  skill 
  and 
  care 
  in 
  prepar- 
  

   ing 
  such 
  delicate 
  sections. 
  In 
  all 
  these 
  sections 
  the 
  brain 
  was 
  not 
  pre- 
  

   viously 
  removed 
  from 
  the 
  head, 
  but 
  the 
  entire 
  head 
  was 
  cut 
  through, 
  

   having 
  previously 
  been 
  hardened 
  in 
  absolute 
  alcohol 
  for 
  twenty-four 
  

   hours 
  or 
  more, 
  and 
  then 
  soaked 
  in 
  gum 
  arabic 
  for 
  one 
  or 
  two 
  or 
  more 
  

   days. 
  The 
  objects 
  were 
  then 
  embedded 
  in 
  a 
  preparation 
  of 
  paraffine 
  and 
  

   sweet-oil 
  and 
  wax, 
  or, 
  in 
  some 
  cases, 
  in 
  soap 
  and 
  oil. 
  After 
  the 
  sections 
  

   were 
  cut 
  they 
  were 
  stained 
  with 
  picrocarmine, 
  or 
  partially 
  stained 
  with 
  

   osmic 
  acid, 
  and 
  then 
  treated 
  with 
  picrocarmine. 
  Finally 
  the 
  slices 
  were 
  

   mounted 
  in 
  glycerine 
  jelly 
  for 
  study 
  under 
  the 
  microscope. 
  

  

  The 
  sections 
  were 
  in 
  most 
  cases 
  frontal 
  ones, 
  namely, 
  cut 
  transversely 
  

   from 
  the 
  front 
  of 
  the 
  head 
  or 
  brain 
  backwards, 
  while 
  a 
  few 
  were 
  longi- 
  

   tudinal 
  or 
  vertical 
  ones, 
  viz, 
  cut 
  parallel 
  to 
  the 
  median 
  line 
  of 
  the 
  body. 
  

   They 
  were 
  either 
  -^ 
  or 
  yoVo- 
  of 
  an 
  inch 
  in 
  thickness. 
  

  

  It 
  should 
  be 
  observed 
  that 
  the 
  brain 
  is 
  divided 
  by 
  a 
  furrow 
  into 
  two 
  

   halves 
  or 
  hemispheres 
  ; 
  these 
  are 
  deepest 
  above 
  and 
  below, 
  and 
  the 
  

   upper 
  and 
  lower 
  portions 
  may 
  be 
  called, 
  respectively, 
  the 
  frontal 
  and 
  

   posterior 
  furrow. 
  

  

  The 
  brain 
  is 
  mostly 
  surrounded 
  by 
  a 
  thin 
  delicate 
  membrane, 
  the 
  neu- 
  

   rilemma, 
  also 
  called 
  by 
  Krieger 
  the 
  perineurium 
  ; 
  it 
  is 
  formed 
  of 
  very 
  

   dense 
  fibrous 
  connective 
  tissue. 
  

  

  Histological 
  elements 
  of 
  the 
  brain. 
  — 
  The 
  brain 
  is 
  histologically 
  or 
  struct- 
  

   urally 
  divided 
  into 
  two 
  kinds 
  of 
  tissue 
  or 
  cellular 
  elements. 
  

  

  I. 
  An 
  outer, 
  slightly 
  darker, 
  usually 
  pale 
  grayish 
  white 
  portion 
  is 
  

   made 
  up 
  of 
  " 
  cortical 
  cells," 
  or 
  " 
  ganglion 
  cells." 
  (PI. 
  XI, 
  Fig. 
  3, 
  a, 
  b, 
  c, 
  d.) 
  

   This 
  portion 
  is 
  stained 
  red 
  by 
  carmine, 
  the 
  ganglion 
  cells 
  composing 
  it 
  

   readily 
  taking 
  the 
  stain 
  ; 
  when 
  thus 
  stained 
  by 
  carmine, 
  the 
  nucleus 
  of 
  

   the 
  cells 
  is 
  rendered 
  quite 
  distinct, 
  but 
  the 
  cell 
  wall 
  is 
  also 
  distinct 
  ; 
  

   when 
  stained 
  by 
  hsematoxylin 
  the 
  large 
  nuclei 
  are 
  remarkably 
  distinct, 
  

   but 
  the 
  cell 
  walls 
  are 
  not 
  well 
  brought 
  out 
  ; 
  when 
  stained 
  by 
  osmic 
  acid 
  

   these 
  cells 
  are 
  not 
  so 
  clearly 
  shown 
  as 
  by 
  a 
  picrocarmine 
  or 
  carmine 
  

   stain, 
  and 
  the 
  nucleus 
  is 
  less 
  distinct 
  than 
  when 
  treated 
  by 
  the 
  two 
  other 
  

   stains 
  mentioned. 
  

  

  This 
  outer 
  loose 
  cellular 
  envelope 
  of 
  the 
  brain 
  consists 
  of 
  large 
  and 
  

   small 
  ganglion 
  cells. 
  Where 
  the 
  tissue 
  consists 
  of 
  small 
  ganglion 
  cells, 
  

   it 
  is 
  naturally 
  from 
  the 
  denser 
  arrangement 
  of 
  the 
  smaller 
  cells, 
  which 
  

   are 
  packed 
  closer 
  together, 
  rather 
  darker 
  than 
  in 
  those 
  regions 
  where 
  the 
  

   tissue 
  consists 
  of 
  the 
  more 
  loosely 
  disposed, 
  large 
  ganglion 
  cells. 
  

  

  