﻿274 
  REPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  Bobretsky's 
  method, 
  at 
  intervals 
  of 
  a 
  day 
  until, 
  say, 
  the 
  expiration 
  of 
  

   ten 
  days. 
  

  

  The 
  specimens 
  were 
  preserved 
  in 
  alcohol 
  of 
  ordinary 
  strength, 
  not 
  

   having 
  been 
  hardened 
  by 
  any 
  reagent, 
  such 
  as 
  chromic 
  acid, 
  and 
  the 
  sec- 
  

   tions 
  were 
  cut 
  by 
  Mr. 
  N. 
  !N". 
  Mason, 
  of 
  Providence, 
  who, 
  after 
  having 
  

   hardened 
  the 
  eggs 
  in 
  absolute 
  alcohol, 
  then 
  placed 
  them 
  in 
  dissolved 
  

   gum 
  arable, 
  having 
  previous 
  to 
  cutting 
  stained 
  the 
  eggs 
  in 
  picro- 
  

   carmine. 
  

  

  The 
  embryo 
  was 
  cut 
  into 
  thirty-four 
  sections, 
  some 
  of 
  them 
  passing 
  

   through 
  the 
  Jimbs 
  (see 
  PI. 
  XX, 
  Fig. 
  1), 
  which 
  shows 
  that 
  the 
  procephalic 
  

   lobes, 
  the 
  mouth 
  parts 
  and 
  legs 
  had 
  been 
  indicated, 
  and 
  that 
  the 
  embryo 
  

   was 
  nearly 
  as 
  far 
  advanced 
  as 
  that 
  represented 
  on 
  PI. 
  XYI, 
  Fig. 
  1. 
  

  

  Nervous 
  system 
  and 
  eyes. 
  — 
  At 
  this 
  time 
  the 
  nervous 
  system 
  is 
  well 
  

   developed, 
  the 
  brain 
  being 
  now 
  nearly 
  as 
  large 
  in 
  proportion 
  to 
  the 
  head 
  

   and 
  to 
  the 
  succeeding 
  segments 
  as 
  in 
  the 
  nearly 
  mature 
  larvse 
  figured 
  in 
  

   the 
  chapter 
  on 
  the 
  brain 
  of 
  the 
  locust 
  in 
  the 
  Second 
  Keport 
  of 
  the 
  United 
  

   States 
  Entomological 
  Commission, 
  Plate 
  XII. 
  At 
  this 
  time, 
  as 
  seen 
  in 
  

   PI. 
  XX, 
  Fig. 
  1, 
  the 
  two 
  hemispheres 
  of 
  the 
  brain 
  {br) 
  are 
  indicated, 
  but 
  

   there 
  are 
  as 
  yet 
  no 
  signs 
  of 
  a 
  differentiation 
  of 
  the 
  brain 
  into 
  the 
  cere- 
  

   bral 
  lobes 
  and 
  antennal 
  lobes 
  of 
  the 
  advanced 
  embryo 
  figured 
  on 
  PI. 
  XII 
  

   of 
  our 
  Second 
  Keport. 
  

  

  The 
  optic 
  ganglia 
  (Fig. 
  1, 
  op. 
  g.) 
  are 
  large, 
  and, 
  like 
  the 
  brain, 
  com- 
  

   posed 
  of 
  minute 
  ganglion-cells. 
  The 
  subcesophageal 
  ganglion 
  is 
  now 
  

   about 
  twice 
  as 
  large 
  as 
  those 
  of 
  the 
  ventral 
  cord. 
  A 
  section 
  of 
  one 
  of 
  

   the 
  thoracic 
  ganglia 
  is 
  represented 
  on 
  PI. 
  XIX, 
  Fig. 
  3. 
  

  

  The 
  eyes 
  are 
  now 
  clearly 
  indicated 
  and 
  of 
  comparatively 
  large 
  size 
  

   (PI. 
  XX, 
  Fig. 
  1). 
  The 
  rows 
  of 
  cells 
  radiating 
  outward 
  from 
  the 
  periphery 
  

   of 
  the 
  optic 
  ganglion 
  are 
  well 
  indicated, 
  showing 
  that 
  at 
  this 
  date 
  and 
  

   probably 
  at 
  an 
  earlier 
  i)eriod 
  the 
  separate 
  divisions, 
  or 
  those 
  correspond- 
  

   ing 
  to 
  the 
  simple 
  eyes, 
  are 
  indicated. 
  The 
  eyes 
  of 
  the 
  embryo 
  of 
  0, 
  

   spretus 
  at 
  a 
  later 
  date 
  are 
  represented 
  at 
  PI. 
  XYI, 
  Fig. 
  4, 
  when 
  the 
  

   cones 
  and 
  rods 
  are 
  clearly 
  developed. 
  

  

  TJie 
  heart 
  is 
  now 
  well 
  developed 
  (PI. 
  XX, 
  Figs. 
  3 
  and 
  4), 
  and 
  from 
  

   what 
  we 
  have 
  seen, 
  as 
  indicated 
  in 
  Fig. 
  4, 
  the 
  mode 
  of 
  origin 
  is 
  as 
  

   claimed 
  by 
  Dohrn. 
  As 
  seen 
  by 
  the 
  section 
  represented 
  by 
  Fig. 
  4, 
  the 
  

   walls 
  of 
  the 
  heart 
  at 
  this 
  time 
  are 
  formed 
  of 
  a 
  continuation 
  of 
  the 
  am- 
  

   nion 
  which 
  merges 
  into 
  the 
  walls 
  of 
  the 
  heart. 
  The 
  membrane 
  form- 
  

   ing 
  the 
  heart 
  is 
  formed 
  beneath 
  and 
  above 
  of 
  a 
  single 
  row 
  of 
  epithelial 
  

   cells, 
  which 
  on 
  the 
  sides 
  become 
  double, 
  or, 
  as 
  seen 
  on 
  the 
  right 
  side 
  

   of 
  the 
  figure, 
  about 
  four 
  rows 
  deep. 
  From 
  this 
  it 
  would 
  appear 
  that 
  

   the 
  view 
  of 
  Dohrn 
  that 
  the 
  heart 
  originates 
  as 
  a 
  loop 
  of 
  the 
  ectoblast, 
  

   which 
  becomes 
  constricted 
  and 
  finally 
  forms 
  a 
  separate 
  tube, 
  is 
  a 
  more 
  

   correct 
  one 
  than 
  the 
  opinion 
  of 
  Kowalevsky 
  that 
  it 
  is 
  formed 
  by 
  the 
  

   union 
  of 
  what 
  were 
  originally 
  independent 
  mesoblastcells. 
  The 
  con- 
  

   tents 
  of 
  the 
  heart 
  are 
  very 
  finely 
  granular, 
  the 
  granules 
  as 
  a 
  rule 
  not 
  

   much 
  if 
  any 
  larger 
  than 
  those 
  in 
  the 
  small 
  cells 
  forming 
  the 
  amnion 
  or 
  

  

  