﻿TENT 
  CATERPILLAR 
  — 
  SNODGRASS. 
  357 
  

  

  All 
  the 
  external 
  parts 
  of 
  the 
  insect 
  are 
  formed 
  from 
  the 
  skin 
  and 
  

   its 
  hard 
  outer 
  cuticle. 
  The 
  skin 
  consists 
  of 
  a 
  layer 
  of 
  cells 
  and 
  is 
  

   called 
  the 
  hypodermis. 
  The 
  remodeling 
  of 
  the 
  external 
  form 
  and 
  

   organs 
  results 
  from 
  a 
  regeneration 
  of 
  the 
  hypoderm. 
  After 
  the 
  ex- 
  

   ternal 
  parts 
  of 
  any 
  stage 
  are 
  once 
  formed 
  they 
  do 
  not 
  change 
  again 
  

   during 
  that 
  stage, 
  but 
  there 
  are 
  certain 
  islands 
  of 
  cells 
  in 
  the 
  hypo- 
  

   derm 
  that 
  retain 
  their 
  vitality 
  till 
  the 
  propupal 
  period. 
  At 
  the 
  be- 
  

   ginning 
  of 
  metamorphosis 
  these 
  cells 
  begin 
  to 
  multiply 
  rapidly 
  and 
  

   spread 
  out 
  in 
  expanding 
  patches 
  of 
  new 
  skin. 
  The 
  old 
  skin 
  cells 
  

   appear 
  to 
  be 
  discouraged 
  at 
  the 
  sight 
  of 
  these 
  vigorous 
  young 
  cells 
  

   crowding 
  upon 
  them; 
  they 
  give 
  up 
  at 
  once 
  without 
  a 
  fight, 
  go 
  to 
  

   pieces, 
  and 
  are 
  absorbed 
  into 
  the 
  interior 
  of 
  the 
  body 
  as 
  the 
  new 
  

   cells 
  take 
  their 
  places. 
  The 
  islands 
  from 
  which 
  the 
  latter 
  originated 
  

   were 
  parts 
  of 
  the 
  original 
  body 
  segments, 
  and 
  each 
  new 
  growing 
  set 
  

   respects 
  the 
  boundaries 
  of 
  its 
  own 
  segment, 
  but 
  pays 
  no 
  attention 
  to 
  

   the 
  old 
  shape 
  of 
  the 
  segment 
  or 
  any 
  of 
  its 
  parts. 
  Thus 
  the 
  newly 
  

   formed 
  insect 
  has 
  the 
  same 
  segmentation 
  as 
  in 
  the 
  preceding 
  stage, 
  

   but 
  its 
  shape 
  and 
  details 
  may 
  be 
  very 
  different. 
  

  

  During 
  all 
  this 
  modification 
  of 
  the 
  hypodermis 
  the 
  old 
  cuticle 
  cov- 
  

   ering 
  it 
  has 
  remained 
  the 
  same. 
  When 
  the 
  new 
  hypoderm 
  is 
  com- 
  

   pleted, 
  the 
  old 
  caterpillar 
  cuticle 
  is 
  loosened 
  and 
  separated, 
  while 
  a 
  

   new 
  cuticle 
  is 
  formed 
  beneath 
  it 
  on 
  the 
  surface 
  of 
  the 
  new 
  skin. 
  This 
  

   gives 
  the 
  wing 
  buds 
  a 
  chance 
  to 
  evert 
  and 
  take 
  their 
  normal 
  position 
  

   outside 
  the 
  body. 
  Then 
  the 
  old 
  cuticle 
  is 
  shed 
  and 
  the 
  newly 
  formed 
  

   creature 
  is 
  exposed 
  in 
  the 
  shape 
  of 
  the 
  pupa. 
  

  

  The 
  original 
  islands 
  of 
  regeneration 
  cells 
  are 
  called 
  imaginal 
  buds 
  

   (from 
  imago, 
  meaning 
  an 
  adult). 
  During 
  the 
  pupal 
  stage 
  the 
  hypo- 
  

   derm 
  undergoes 
  still 
  further 
  modifications, 
  and 
  forms 
  still 
  another 
  

   cuticle 
  beneath 
  that 
  of 
  the 
  pupa. 
  Finally, 
  the 
  latter 
  is 
  cast 
  off, 
  and 
  

   the 
  moth 
  appears. 
  

  

  But 
  while 
  this 
  remodeling 
  of 
  the 
  external 
  form 
  has 
  been 
  going 
  on 
  

   other 
  changes 
  have 
  taken 
  place 
  inside 
  the 
  body. 
  We 
  have 
  already 
  

   noted 
  that 
  the 
  lining 
  of 
  the 
  stomach 
  is 
  shed 
  at 
  the 
  time 
  when 
  the 
  

   caterpillar 
  is 
  spinning 
  its 
  cocoon. 
  But 
  it 
  is 
  not 
  all 
  cast 
  off 
  — 
  groups 
  

   of 
  small 
  cells 
  which, 
  like 
  those 
  of 
  the 
  hypoderm, 
  have 
  not 
  lost 
  their 
  

   vitality 
  remain 
  behind 
  and 
  generate 
  a 
  new 
  lining 
  that 
  digests 
  and 
  

   absorbs 
  the 
  debris 
  of 
  the 
  old. 
  The 
  gullet, 
  with 
  the 
  crop 
  and 
  the 
  

   intestine, 
  being 
  ingrowths 
  of 
  the 
  hypoderm, 
  are 
  regenerated 
  in 
  the 
  

   same 
  way 
  as 
  the 
  body 
  wall. 
  Groups 
  of 
  cells 
  in 
  their 
  walls 
  multiply 
  

   and 
  replace 
  the 
  old 
  cells, 
  which 
  are 
  absorbed 
  into 
  the 
  blood. 
  Their 
  

   linings 
  are 
  shed 
  with 
  the 
  body 
  cuticle. 
  The 
  alimentary 
  canal 
  of 
  the 
  

   moth 
  is 
  very 
  different 
  from 
  that 
  of 
  the 
  caterpillar, 
  but 
  it 
  will 
  be 
  de- 
  

   scribed 
  in 
  the 
  next 
  section. 
  

  

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