﻿354 
  ANNUAL, 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1922. 
  

  

  and 
  during 
  the 
  next 
  three 
  or 
  four 
  days 
  a 
  characteristic 
  change 
  of 
  

   form 
  takes 
  place. 
  As 
  the 
  body 
  continues 
  to 
  shorten, 
  the 
  first 
  three 
  

   segments 
  become 
  crowded 
  together, 
  but 
  those 
  of 
  the 
  abdominal 
  

   region 
  swell 
  out 
  and 
  their 
  legs 
  are 
  retracted. 
  The 
  creature 
  (fig. 
  17,. 
  

   B) 
  is 
  now 
  only 
  half 
  its 
  former 
  length 
  (A) 
  and 
  would 
  scarcely 
  be 
  

   recognized 
  as 
  the 
  same 
  animal 
  that 
  spun 
  itself 
  into 
  the 
  cocoon. 
  

  

  This 
  period 
  of 
  the 
  insect's 
  life 
  is 
  called 
  the 
  prepupal 
  stage 
  of 
  the 
  

   caterpillar. 
  Yet 
  the 
  creature 
  is 
  really 
  no 
  longer 
  a 
  caterpillar, 
  it 
  is 
  

   simply 
  still 
  wearing 
  the 
  caterpillar's 
  skin 
  ; 
  and 
  this 
  garment 
  can 
  now 
  

   be 
  taken 
  off 
  like 
  a 
  coat 
  without 
  injury 
  to 
  the 
  wearer. 
  The 
  latter 
  

   (fig. 
  17, 
  C) 
  is 
  then 
  discovered 
  to 
  be 
  a 
  thing 
  entirety 
  different 
  in 
  ap- 
  

   pearance 
  from 
  the 
  caterpillar 
  (A). 
  In 
  many 
  ways 
  it 
  suggests 
  the 
  

   future 
  moth 
  (E) 
  , 
  but 
  it 
  is 
  called 
  the 
  propupa. 
  It 
  has 
  a 
  pair 
  of 
  small 
  

   wings 
  (W 
  2 
  and 
  W 
  3 
  ) 
  on 
  each 
  side 
  of 
  the 
  body, 
  legs 
  (L) 
  much 
  longer 
  

   than 
  those 
  of 
  the 
  caterpillar 
  (being 
  folded, 
  only 
  the 
  ends 
  are 
  visible 
  in 
  

   side 
  view), 
  and 
  a 
  pair 
  of 
  large 
  antennae 
  (Ant) 
  on 
  the 
  head. 
  Its 
  first 
  

   three 
  body 
  segments, 
  though 
  all 
  different 
  from 
  one 
  another, 
  consti- 
  

   tute 
  a 
  well-defined 
  thoracic 
  region 
  bearing 
  the 
  wings 
  and 
  legs, 
  while 
  

   the 
  following 
  10 
  segments 
  are 
  more 
  alike 
  than 
  in 
  the 
  caterpillar 
  and 
  

   form 
  a 
  distinct 
  abdominal 
  part 
  of 
  the 
  body, 
  swollen 
  at 
  the 
  middle 
  

   and 
  tapering 
  toward^ 
  the 
  rear 
  end. 
  The 
  breathing 
  pores 
  along 
  the 
  

   sides 
  of 
  the 
  body 
  correspond 
  with 
  those 
  of 
  the 
  caterpillar, 
  except 
  

   that 
  there 
  is 
  an 
  extra 
  pore 
  on 
  each 
  side 
  between 
  the 
  second 
  and 
  third 
  

   segments 
  (but 
  covered 
  bj 
  r 
  the 
  base 
  of 
  the 
  front 
  wing 
  in 
  the 
  figure, 
  C). 
  

   This 
  spiracle 
  is 
  present 
  in 
  most 
  insects, 
  both 
  young 
  and 
  adult, 
  and 
  

   is 
  simply 
  overgrown 
  by 
  the 
  skin 
  in 
  the 
  caterpillar. 
  

  

  Many 
  important 
  alterations 
  have 
  taken 
  place 
  in 
  the 
  form 
  and 
  

   structure 
  of 
  the 
  head 
  and 
  the 
  appendages 
  about 
  the 
  mouth 
  during 
  

   the 
  change 
  from 
  the 
  caterpillar, 
  as 
  will 
  be 
  seen 
  by 
  comparing 
  Figure 
  

   17, 
  H, 
  with 
  Figure 
  11. 
  Most 
  of 
  the 
  sides 
  of 
  the 
  caterpillar's 
  head, 
  

   including 
  its 
  12 
  eyes, 
  have 
  been 
  converted 
  into 
  the 
  two 
  huge 
  eyes 
  

   (E) 
  of 
  the 
  propupa, 
  and 
  the 
  antenna? 
  (Ant) 
  have 
  increased 
  enor- 
  

   mously 
  in 
  size. 
  The 
  upper 
  lip 
  (Lm), 
  on 
  the 
  other 
  hand, 
  is 
  much 
  

   smaller 
  in 
  the 
  propupa, 
  the 
  great 
  biting 
  jaws 
  of 
  the 
  caterpillar 
  are 
  

   reduced 
  to 
  mere 
  rudiments 
  (Md), 
  while 
  the 
  spinneret 
  of 
  the 
  cater- 
  

   pillar 
  (Spn) 
  is 
  gone 
  entirely. 
  The 
  maxillae 
  (Mx) 
  and 
  labium 
  (Lb) 
  

   are 
  more 
  distinct 
  from 
  one 
  another, 
  and 
  their 
  parts 
  more 
  simplified. 
  

   The 
  labium 
  carries 
  two 
  long 
  palpi 
  (fig. 
  17, 
  H, 
  LbPlp). 
  

  

  Yet, 
  as 
  different 
  as 
  are 
  the 
  external 
  parts 
  of 
  the 
  propupa 
  from 
  

   those 
  of 
  the 
  caterpillar, 
  they 
  have 
  all 
  been 
  formed 
  in 
  the 
  correspond- 
  

   ing 
  organs 
  of 
  the 
  latter, 
  or 
  at 
  least 
  as 
  far 
  as 
  there 
  was 
  room 
  for 
  them 
  

   to 
  grow 
  in 
  the 
  caterpillar 
  parts. 
  In 
  the 
  case 
  of 
  the 
  antennae 
  only 
  

   the 
  very 
  tips 
  of 
  the 
  new 
  organs 
  could 
  develop 
  in 
  the 
  old, 
  the 
  rest 
  

   had 
  to 
  fold 
  back 
  against 
  the 
  sides 
  of 
  the 
  head 
  beneath 
  the 
  skin. 
  

  

  