﻿348 
  

  

  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1922. 
  

  

  The 
  general 
  external 
  form 
  and 
  structure 
  of 
  a 
  caterpillar 
  may 
  be 
  

   learned 
  from 
  a 
  study 
  of 
  Figure 
  17, 
  A. 
  But 
  the 
  external 
  organs 
  of 
  

   chief 
  interest 
  are 
  those 
  of 
  the 
  head 
  (fig. 
  11), 
  including 
  the 
  mouth, 
  

   the 
  jaws, 
  and 
  the 
  silk-spinning 
  instrument. 
  The 
  facial 
  view 
  (A) 
  

   shows 
  the 
  notched 
  upper 
  lip 
  or 
  labrum 
  (Lm) 
  suspended 
  from 
  the 
  

   triangular 
  frontal 
  plate 
  (Ft) 
  like 
  a 
  protective 
  flap 
  over 
  the 
  bases 
  

   of 
  the 
  jaws. 
  The 
  latter, 
  called 
  mandibles 
  (Md), 
  are 
  large, 
  heavy 
  

   appendages 
  at 
  the 
  sides 
  of 
  the 
  mouth, 
  swinging 
  out 
  and 
  in 
  on 
  two 
  

   ball-and-socket 
  hinges. 
  The 
  muscles 
  that 
  move 
  them 
  are 
  shown 
  in 
  

   Figure 
  12, 
  A. 
  The 
  cutting 
  edge 
  of 
  each 
  mandible 
  carries 
  a 
  number 
  

   of 
  strong 
  teeth. 
  At 
  the 
  sides 
  of 
  the 
  jaws 
  are 
  the 
  two 
  small 
  three- 
  

   jointed 
  antennae 
  (fig. 
  11, 
  Ant). 
  The 
  caterpillar 
  has 
  12 
  very 
  small 
  

   eyes, 
  one 
  near 
  the 
  base 
  of 
  each 
  antenna 
  and 
  the 
  others 
  in 
  two 
  groups 
  

  

  of 
  5 
  each 
  on 
  the 
  sides 
  of 
  the 
  head 
  (fig. 
  11, 
  

   A, 
  O). 
  But 
  with 
  all 
  its 
  eyes 
  the 
  cater- 
  

   pillar 
  appears 
  to 
  be 
  very 
  nearsighted 
  and 
  

   gives 
  little 
  evidence 
  of 
  being 
  able 
  to 
  see 
  

   more 
  than 
  the 
  difference 
  between 
  light 
  

   and 
  darkness. 
  Those 
  tent 
  caterpillars 
  

   that 
  were 
  starving 
  on 
  the 
  denuded 
  tree 
  

   failed 
  to 
  perceive 
  other 
  food 
  trees 
  in 
  full 
  

   leaf 
  only 
  a 
  few 
  feet 
  away. 
  

  

  The 
  large 
  complex 
  organ 
  that 
  projects 
  

   behind 
  or 
  below 
  the 
  mouth 
  like 
  a 
  thick 
  

   under 
  lip 
  (fig. 
  11, 
  C) 
  is 
  a 
  combination 
  

   of 
  three 
  parts 
  that 
  are 
  separate 
  in 
  other 
  

   insects. 
  These 
  are 
  a 
  second 
  pair 
  of 
  soft 
  

   jaws, 
  called 
  maxillae 
  (B, 
  C, 
  Mx), 
  and 
  the 
  

   true 
  under 
  lip, 
  or 
  labium 
  (Lb). 
  The 
  

   most 
  important 
  part 
  of 
  this 
  combined 
  structure 
  in 
  the 
  caterpillar, 
  

   however, 
  is 
  the 
  hollow 
  spine 
  (A, 
  B, 
  C, 
  Spn) 
  pointed 
  downward 
  

   and 
  backward 
  from 
  the 
  end 
  of 
  the 
  labium. 
  This 
  is 
  the 
  spinneret. 
  

   From 
  it 
  issues 
  the 
  silk 
  thread 
  with 
  which 
  the 
  caterpillar 
  weaves 
  its 
  

   tent 
  and 
  its 
  cocoon. 
  

  

  The 
  fresh 
  silk 
  is 
  a 
  liquid 
  formed 
  in 
  long 
  tubular 
  glands 
  extending 
  

   back 
  in 
  the 
  body 
  of 
  the 
  caterpillar 
  to 
  the 
  tenth 
  segment 
  (fig. 
  13, 
  A, 
  

   Gl) 
  . 
  The 
  middle 
  part 
  of 
  each 
  tube 
  is 
  enlarged 
  into 
  a 
  reservoir 
  

   (Res), 
  where 
  the 
  silk 
  liquid 
  may 
  accumulate, 
  and 
  the 
  first 
  part 
  con- 
  

   sists 
  of 
  a 
  narrow 
  duct 
  (Dct) 
  which 
  unites 
  with 
  the 
  duct 
  from 
  the 
  

   other 
  gland 
  in 
  a 
  thick- 
  walled 
  sac 
  (Pr) 
  that 
  finally 
  opens 
  into 
  the 
  

   spinneret. 
  Two 
  small 
  glands, 
  which 
  look 
  like 
  bunches 
  of 
  grapes 
  

   (GIF), 
  open 
  into 
  the 
  ducts 
  near 
  their 
  front 
  ends. 
  

  

  The 
  relation 
  of 
  the 
  ducts 
  and 
  the 
  sac 
  to 
  the 
  spinneret 
  is 
  seen 
  in 
  

   the 
  side 
  view 
  of 
  the 
  maxilla 
  and 
  labium 
  shown 
  at 
  B 
  in 
  Figure 
  13. 
  

  

  -The 
  mandibles 
  or 
  

   of 
  the 
  caterpillar 
  de- 
  

   the 
  head 
  

  

  A, 
  

  

  Fig. 
  12. 
  

   jaws 
  

  

  tached 
  from 
  

   front 
  view 
  of 
  right 
  man- 
  

   dible 
  ; 
  B, 
  underside 
  of 
  the 
  

   left, 
  a 
  and 
  p, 
  the 
  socket 
  

   and 
  knob 
  that 
  hinge 
  the 
  

   jaw 
  to 
  the 
  head 
  ; 
  EMcl 
  

   and 
  RMcl, 
  extensor 
  and 
  re- 
  

   tractor 
  muscles 
  that 
  move 
  

   the 
  jaw. 
  

  

  