﻿EMBRYONAL 
  MEMBRANES 
  OF 
  INSECTS. 
  

  

  265 
  

  

  The 
  following 
  diagrammatic 
  view, 
  copied 
  from 
  Graber, 
  will 
  render 
  

   clearer 
  these 
  statements 
  : 
  

  

  Germinal 
  vesicle. 
  

  

  Germinal 
  cells. 
  

  

  Outer 
  germinal 
  cells 
  

   (blastoderm). 
  

  

  Inner 
  germinal 
  cells 
  

   (primary). 
  

  

  Ectoderm. 
  

  

  Mesoderm. 
  

  

  Inner 
  germinal 
  cells 
  

   (secondary). 
  

  

  Embryonal 
  membranes. 
  — 
  After 
  the 
  primitive 
  band 
  is 
  formed, 
  the 
  blasto- 
  

   derm 
  twice 
  molts 
  or 
  jcasts 
  gft' 
  a 
  layer 
  of 
  cells. 
  The 
  first 
  molt 
  is 
  before 
  the 
  

   limbs 
  bud 
  out, 
  and 
  is 
  called 
  the 
  outer 
  or 
  serous 
  membrane. 
  (PI. 
  XXII, 
  

   Fig. 
  2, 
  ser.) 
  It 
  is 
  at 
  first 
  cellular, 
  the 
  nuclei 
  finally 
  disappearing 
  as 
  it 
  

   stretches 
  and 
  covers 
  the 
  growing 
  embryo. 
  The 
  inner, 
  called 
  the 
  amnion 
  

   (PI. 
  XXII^ 
  Fig. 
  2, 
  ttm), 
  is 
  more 
  closely 
  connected 
  with 
  the 
  embryo; 
  origin- 
  

   ally 
  connected 
  with 
  the 
  serous 
  membrane, 
  it 
  splits 
  off 
  from 
  the 
  primi- 
  

   tive 
  band 
  about 
  the 
  time 
  the 
  appendages 
  begin 
  to 
  bud 
  out, 
  and 
  continues 
  

   to 
  closely 
  envelop 
  the 
  body 
  and 
  appendages, 
  as 
  seen 
  in 
  PI. 
  XXII, 
  Fig. 
  2. 
  

   Both 
  of 
  these 
  membranes 
  are, 
  at 
  the 
  time 
  of 
  hatching, 
  cast 
  off 
  with 
  the 
  

   egg-shell 
  or 
  chorion, 
  ^^^ 
  and 
  the 
  exochorion 
  or 
  polygonal 
  outer 
  crust 
  which 
  

   envelops 
  the 
  shell 
  or 
  chorion 
  proper, 
  and 
  which 
  is 
  so 
  well 
  developed 
  in 
  

   the 
  ^gg 
  of 
  the 
  locust. 
  Hence 
  we 
  have 
  eight 
  layers 
  in 
  the 
  insect 
  during 
  

   embryonic 
  life 
  : 
  

  

  1. 
  Exochorion. 
  (Eemains 
  of 
  the 
  epithelium 
  of 
  the 
  ovarian 
  follicle.) 
  

  

  2. 
  Chorion. 
  (Egg-shell 
  or 
  cuticle 
  secreted 
  in 
  the 
  ovarian 
  follicle.) 
  

  

  3. 
  Vitelline 
  membrane. 
  (Primary 
  egg-membrane. 
  Yolk-skin 
  ) 
  

  

  4. 
  Serous 
  or 
  outer 
  germ-membrane. 
  (Blastodermic 
  ") 
  

  

  molt.) 
  j 
  

  

  Amnion. 
  Inner 
  germ-membrane. 
  Oast 
  from 
  | 
  Derived 
  from 
  

  

  the 
  primitive 
  band. 
  [> 
  the 
  blasto- 
  

  

  Ectoderm. 
  ") 
  | 
  derm. 
  

  

  Mesoderm. 
  j> 
  Embryo. 
  j 
  

  

  Endoderm. 
  ^ 
  ^ 
  

  

  123 
  For 
  an 
  account 
  of 
  the 
  egg 
  and 
  its 
  outer 
  crust 
  or 
  exochorion, 
  and 
  the 
  mode 
  of 
  hatching, 
  see 
  1st 
  Ee- 
  

   poit 
  of 
  the 
  Commission, 
  pp. 
  277, 
  278. 
  

  

  