﻿CHAPTER 
  X. 
  

  

  THE 
  EMBRYOLOGICAL 
  DEVELOPMENT 
  OF 
  THE 
  LOCUST. 
  

  

  Plates 
  XYI-XXI. 
  

  

  In 
  order 
  that 
  the 
  reader 
  may 
  understand 
  the 
  following 
  statements 
  re- 
  

   garding 
  the 
  embryology 
  of 
  the 
  locust, 
  which 
  are 
  more 
  or 
  less 
  fragmentary 
  

   in 
  their 
  nature, 
  we 
  preface 
  our 
  account 
  with 
  a 
  brief 
  description 
  of 
  the 
  de- 
  

   velopmental 
  history 
  of 
  winged 
  insects 
  in 
  general 
  so 
  far 
  as 
  it 
  is 
  now 
  known. 
  

  

  Formation 
  of 
  the 
  hlastoderm. 
  — 
  The 
  changes 
  which 
  take 
  place 
  in 
  the 
  

   egg 
  immediately 
  after 
  fertilization 
  are 
  not 
  known 
  beyond 
  the 
  fact 
  that 
  

   segmentation 
  of 
  the 
  yolk 
  is 
  partial, 
  being 
  confined 
  to 
  the 
  periphery. 
  The 
  

   only 
  observations 
  yet 
  published 
  are 
  those 
  of 
  Bobretsky 
  ^^^ 
  on 
  a 
  butterfly 
  

   {Fieris 
  cratcegi) 
  and 
  a 
  moth 
  {Forthesia 
  chrysorrhoea). 
  After 
  fertilization 
  

   there 
  first 
  appear 
  scattered 
  through 
  the 
  yolk 
  a 
  few 
  (the 
  smallest 
  number 
  

   4) 
  cell-like, 
  minute, 
  amoeboid 
  masses 
  of 
  protoplasm, 
  each 
  with 
  a 
  distinct 
  

   nucleus. 
  A 
  few 
  (one 
  at 
  least) 
  of 
  these 
  bodies 
  gradually 
  pass 
  out 
  of 
  the 
  

   center 
  of 
  the 
  yolk 
  to 
  the 
  surface 
  of 
  the 
  egg 
  (Fig 
  10 
  A, 
  n)^ 
  these 
  becoming 
  

   larger 
  and 
  rounder, 
  and 
  from 
  one 
  or 
  two 
  of 
  these 
  nuclei 
  (Fig. 
  10 
  B, 
  & 
  c) 
  

   the 
  so-called 
  blastoderm 
  originates 
  (Fig. 
  10 
  0, 
  hi). 
  Those 
  nuclei 
  remain- 
  

   ing 
  in 
  the 
  yolk 
  increase 
  in 
  number 
  and 
  afterwards 
  become 
  the 
  nuclei 
  of 
  

   rounded 
  masses 
  of 
  yolk-granules, 
  forming 
  the 
  so-called 
  yolk-spheres 
  

   which 
  Bobretsky 
  regards 
  as 
  true 
  cells. 
  

  

  To 
  the 
  few 
  blastoderm 
  cells 
  situated 
  on 
  the 
  upper 
  end 
  of 
  the 
  egg 
  are 
  

   added 
  others 
  which 
  continue 
  to 
  pass 
  from 
  the 
  yolk 
  to 
  the 
  periphery, 
  

  

  J21 
  Zeitschrift 
  fiir 
  wissenschaftliche 
  Zoologie, 
  Band 
  xxxi, 
  195. 
  1878. 
  PI. 
  xiv. 
  The 
  mode 
  of 
  origin, 
  

   observed 
  by 
  Bobretsky 
  in 
  the 
  Lepidoptera 
  does 
  not 
  apparently 
  agree 
  in 
  the 
  later 
  stages 
  \vith 
  what 
  

   Weismann 
  has 
  observed 
  in 
  the 
  Diptera, 
  and 
  I 
  have 
  observed 
  in 
  the 
  flea, 
  as 
  there 
  is 
  present 
  a 
  blasteni 
  

   (Weismann) 
  or 
  clear 
  homogeneous 
  layer 
  between 
  the 
  polar 
  cells 
  and 
  the 
  yolk, 
  and 
  afterwards 
  the 
  

   blastoderm 
  appears, 
  the 
  polar 
  cells 
  still 
  persisting. 
  See 
  PI. 
  2, 
  iig. 
  1-3, 
  Packard's 
  Embryol. 
  Studies 
  on 
  

   Hexapodous 
  Insects. 
  Memoirs 
  Peabody 
  Academy 
  of 
  Science, 
  1872. 
  See 
  also 
  Weismann's 
  Entwick- 
  

   elung 
  der 
  Dipteren, 
  Taf, 
  1, 
  fig. 
  3. 
  

  

  263 
  

  

  