﻿TENT 
  CATERPILLAR 
  — 
  SNODGRASS. 
  351 
  

  

  and 
  looks 
  like 
  a 
  small 
  mulberry 
  when 
  passed 
  on 
  into 
  the 
  rectum 
  and 
  

   finally 
  extruded 
  from 
  the 
  body. 
  

  

  The 
  alimentary 
  canal 
  is 
  a 
  tube 
  made 
  of 
  a 
  single 
  layer 
  of 
  cells 
  ex- 
  

   tending 
  through 
  the 
  body; 
  but 
  its 
  outer 
  surface, 
  that 
  toward 
  the 
  

   body 
  cavity, 
  is 
  covered 
  by 
  a 
  muscle 
  layer 
  of 
  lengthwise 
  and 
  cross- 
  

   wise 
  fibers 
  which 
  cause 
  the 
  movement 
  of 
  the 
  food 
  through 
  the 
  canal. 
  

   The 
  gullet 
  and 
  crop 
  and 
  the 
  intestine 
  are 
  lined 
  internally 
  with 
  a 
  thin 
  

   cuticle 
  continuous 
  with 
  that 
  covering 
  the 
  surface 
  of 
  the 
  body, 
  and 
  

   these 
  linings 
  are 
  shed 
  with 
  the 
  body 
  cuticle 
  every 
  time 
  the 
  cater- 
  

   pillar 
  molts. 
  

  

  The 
  Malpighian 
  tubules 
  (fig. 
  14, 
  Mai) 
  are 
  the 
  kidneys 
  of 
  insects: 
  

   they 
  are 
  the 
  excretory 
  organs 
  that 
  remove 
  from 
  the 
  blood 
  the 
  waste 
  

   products 
  containing 
  nitrogen, 
  and 
  discharge 
  them 
  into 
  the 
  intestine 
  

   along 
  with 
  the 
  waste 
  parts 
  of 
  the 
  food 
  from 
  the 
  stomach. 
  Ordi- 
  

   narily 
  the 
  Malpighian 
  tubules 
  are 
  of 
  a 
  whitish 
  color, 
  but 
  just 
  before 
  

   the 
  caterpillar 
  is 
  ready 
  to 
  spin 
  its 
  cocoon 
  they 
  

   become 
  congested 
  with 
  a 
  bright 
  yellow 
  sub- 
  

   stance. 
  Under 
  the 
  microscope 
  this 
  is 
  seen 
  to 
  

   • 
  consist 
  of 
  masses 
  of 
  square, 
  oblong, 
  and 
  rod- 
  

   shaped 
  crystals 
  (fig. 
  15). 
  At 
  this 
  time 
  the 
  

   caterpillar 
  has 
  ceased 
  to 
  feed 
  and 
  the 
  ali- 
  

   mentary 
  canal 
  contains 
  no 
  food 
  or 
  food 
  refuse. 
  

   The 
  intestine, 
  however, 
  becomes 
  filled 
  with 
  the 
  

   yellow 
  mass 
  from 
  the 
  Malpighian 
  tubules 
  ; 
  and 
  

   this 
  is 
  the 
  material 
  with 
  which 
  the 
  caterpillar 
  the 
  Malpighian 
  tubules 
  

   plasters 
  the 
  walls 
  of 
  its 
  cocoon, 
  giving 
  them 
  enjected 
  into 
  the 
  walls 
  

   the 
  yellowish 
  color 
  and 
  stiffened 
  texture. 
  

  

  The 
  yellow 
  powder 
  of 
  the 
  cocoon, 
  therefore, 
  consists 
  of 
  the 
  crystals 
  

   from 
  the 
  Malpighian 
  tubules. 
  

  

  We 
  now 
  come 
  to 
  the 
  question 
  of 
  why 
  the 
  caterpillar 
  eats 
  so 
  much. 
  

   It 
  is 
  almost 
  equivalent 
  to 
  asking, 
  " 
  Why 
  is 
  a 
  caterpillar 
  ? 
  " 
  The 
  

   caterpillar 
  is 
  the 
  feeding 
  stage 
  in 
  the 
  insect's 
  life 
  — 
  eating 
  is 
  its 
  

   business, 
  its 
  reason 
  for 
  being 
  a 
  caterpillar. 
  It 
  eats 
  not 
  only 
  to 
  build 
  

   up 
  its 
  own 
  organs, 
  many 
  of 
  which 
  are 
  to 
  be 
  broken 
  down 
  to 
  furnish 
  

   building 
  material 
  for 
  those 
  of 
  the 
  moth, 
  but 
  it 
  eats 
  also 
  to 
  store 
  up 
  

   within 
  its 
  body 
  certain 
  materials 
  in 
  excess 
  of 
  its 
  own 
  needs, 
  which 
  

   likewise 
  will 
  contribute 
  to 
  the 
  growth 
  of 
  the 
  moth. 
  

  

  The 
  most 
  abundant 
  of 
  the 
  food 
  reserves 
  stored 
  by 
  the 
  caterpillar 
  

   is 
  fat. 
  With 
  insects, 
  however, 
  fat 
  does 
  not 
  accumulate 
  amongst 
  the 
  

   muscles 
  and 
  beneath 
  the 
  skin. 
  Insects 
  never 
  become 
  " 
  fat 
  " 
  in 
  ex- 
  

   terna] 
  appearance. 
  Their 
  fatty 
  products 
  are 
  held 
  in 
  a 
  special 
  organ 
  

   called 
  the 
  fat 
  body. 
  

  

  In 
  the 
  tent 
  caterpillar 
  the 
  fat 
  body 
  consists 
  of 
  a 
  loose 
  cellular 
  net- 
  

   work 
  surrounding 
  the 
  crop 
  and 
  continued 
  backward 
  as 
  a 
  thin 
  sheet. 
  

  

  