﻿158 
  EEPORT 
  UNITED 
  STATES 
  ENTOMOLOGICAL 
  COMMISSION. 
  

  

  under 
  the 
  hinder 
  part 
  of 
  the 
  body. 
  The 
  normal 
  number 
  of 
  such 
  so- 
  

   called 
  prolegsin 
  caterpillars 
  is 
  ten, 
  while 
  the 
  Canker 
  Worms 
  have 
  but 
  

   either 
  four 
  or 
  six. 
  The 
  lack 
  of 
  the 
  foremost 
  prolegs 
  obliges 
  them 
  to 
  

   span 
  or 
  loop 
  in 
  walking, 
  from 
  which 
  habit 
  the 
  characteristic 
  names 
  of 
  

   Span 
  Worms, 
  Measuring 
  Worms, 
  and 
  Geometridw, 
  have 
  been 
  given 
  

   to 
  them 
  as 
  well 
  as 
  to 
  the 
  other 
  members 
  of 
  the 
  family 
  to 
  which 
  they 
  

   belong. 
  

  

  The 
  generic 
  name 
  Geometra^ 
  from 
  which 
  is 
  derived 
  the 
  family 
  name 
  

   <jreometridce 
  (meaning 
  "of 
  the 
  Geometra 
  family") 
  signifies 
  a 
  geometer 
  or 
  

   measurer 
  of 
  the 
  earth. 
  

  

  The 
  name 
  of 
  Geometridm 
  is 
  by 
  many 
  authors 
  at 
  the 
  present 
  day 
  con- 
  

   sidered 
  to 
  apply 
  only 
  to 
  a 
  restricted 
  group 
  in 
  the 
  larger 
  family 
  of 
  the 
  

   Fhalcenidw, 
  while 
  by 
  other 
  authors 
  the 
  same 
  name 
  is 
  applied 
  to 
  the 
  

   larger 
  family. 
  

  

  In 
  either 
  case 
  this 
  larger 
  family 
  is 
  differently 
  sub-divided 
  by 
  different 
  

   authors 
  5 
  thus, 
  Harris 
  places 
  the 
  Canker 
  Worms 
  in 
  the 
  fsimilj 
  Hyherniadcej 
  

   Guenee 
  in 
  the 
  family 
  Hyhernidce^ 
  and 
  Packard 
  ^^ 
  in 
  the 
  subfamily 
  Boar- 
  

   minw. 
  

  

  This 
  family, 
  Geometridce 
  or 
  FhaJcenidrce, 
  forms 
  one 
  of 
  the 
  main 
  sub-divi- 
  

   sions 
  of 
  the 
  order 
  Le^idoptera. 
  

  

  Without 
  describing 
  in 
  detail 
  the 
  structural 
  characters 
  of 
  the 
  order 
  or 
  

   the 
  family, 
  which 
  would 
  be 
  inappropriate 
  in 
  this 
  special 
  work 
  (although, 
  

   of 
  course, 
  the 
  Canker 
  Worms 
  must 
  partake 
  of 
  these 
  characters), 
  we 
  will 
  

   mention 
  here 
  certain 
  particulars 
  wherein 
  the 
  Canker 
  Worms 
  are 
  peculiar 
  

   or 
  specially 
  characterized. 
  

  

  Dr. 
  Packard 
  says 
  that 
  "although 
  it 
  is 
  stated 
  '^^ 
  that 
  the 
  Phalcenidm 
  

   have 
  no 
  ocelli," 
  he 
  has 
  "found 
  that 
  they 
  generally 
  occur 
  in 
  our 
  species; 
  

   though, 
  compared 
  with 
  those 
  of 
  the 
  Noctuidce, 
  they 
  are 
  small, 
  and 
  easily 
  

   overlooked. 
  They 
  are 
  situated 
  very 
  near 
  the 
  eyes, 
  usually 
  on 
  the 
  su- 
  

   ture 
  between 
  the 
  epicranium 
  and 
  occiput. 
  * 
  * 
  * 
  They 
  are 
  present 
  

   or 
  absent 
  in 
  different 
  species 
  of 
  the 
  same 
  genus. 
  * 
  * 
  * 
  it 
  is 
  a 
  ques- 
  

   tion 
  whether 
  they 
  are 
  ever 
  of 
  use 
  to 
  the 
  insect, 
  as, 
  in 
  most 
  cases, 
  they 
  

   appear 
  as 
  if 
  partially 
  aborted, 
  and 
  their 
  presence 
  and 
  absence 
  in 
  different 
  

   species 
  of 
  the 
  same 
  genus 
  show 
  that 
  they 
  are 
  not 
  very 
  essential 
  to 
  the 
  

   life 
  of 
  the 
  insect." 
  

  

  TWO 
  DISTINCT 
  INSECT^ 
  CONCERNED. 
  

  

  There 
  are 
  two 
  distinct 
  species 
  working 
  on 
  our 
  elm 
  and 
  apple-trees 
  as 
  

   well 
  as 
  on 
  some 
  ' 
  few 
  other 
  shade 
  and 
  fruit 
  trees. 
  The 
  two 
  have 
  very 
  

   generally 
  been 
  confounded, 
  and 
  it 
  is 
  very 
  important 
  that 
  their 
  differ- 
  

   ences 
  should 
  be 
  understood 
  and 
  kept 
  in 
  mind. 
  

  

  In 
  our 
  Seventh 
  Annual 
  Peport 
  on 
  the 
  Insects 
  of 
  Missouri, 
  we 
  illus- 
  

   trated 
  and 
  exi)lained 
  the 
  differences 
  in 
  habit 
  and 
  structure 
  between 
  the 
  

   two, 
  and 
  gave 
  a 
  detailed 
  comparative 
  description 
  of 
  these 
  two 
  insects 
  

   in 
  their 
  different 
  stages, 
  the 
  descriptions 
  of 
  the 
  moths 
  being 
  but 
  slightly 
  

  

  <8Monograpli 
  of 
  the 
  Geometrid 
  Motli-», 
  p. 
  397. 
  

  

  49Gueii6e, 
  Uranides 
  et 
  Plialeuites, 
  v. 
  1 
  ; 
  Generalites, 
  p. 
  21. 
  

  

  