﻿Diptera, 
  Hemiptera 
  and 
  Insects 
  related 
  to 
  Neuroptera. 
  95 
  

  

  radial 
  sector 
  recently 
  described 
  in 
  the 
  Ephemerida 
  (Morgan, 
  

   1912, 
  Ann. 
  Ent. 
  Soc. 
  Amer., 
  1912, 
  p. 
  89) 
  point 
  to 
  a 
  rather 
  

   close 
  relationship 
  to 
  the 
  Odonata, 
  in 
  whose 
  wing 
  venation 
  

   a 
  similar 
  condition 
  occurs, 
  although 
  it 
  is 
  unknown 
  among 
  

   other 
  insects. 
  In 
  both 
  Odonata 
  and 
  Ephemerida 
  the 
  

   antennae 
  are 
  usually 
  much 
  reduced, 
  and 
  they 
  do 
  not 
  appear 
  

   to 
  be 
  very 
  large 
  in 
  most 
  of 
  the 
  Palaeodictyoptera. 
  The 
  

   tarsi 
  are 
  composed 
  of 
  not 
  over 
  three 
  segments 
  in 
  many 
  of 
  

   the 
  insects 
  of 
  this 
  section. 
  Many 
  of 
  these 
  insects 
  have 
  

   well-developed 
  ceroi 
  (Bull. 
  Brooklyn 
  Ent. 
  Soc, 
  vol. 
  13, 
  

   p. 
  49), 
  although 
  the 
  cerci 
  of 
  certain 
  Odonata 
  have 
  been 
  

   otherwise 
  interpreted 
  by 
  some 
  investigators. 
  In 
  certain 
  

   Ephemerid 
  and 
  Odonatan 
  nymphs 
  

   traces 
  of 
  a 
  median 
  unpaired 
  terminal 
  

   abdominal 
  filament 
  may 
  be 
  retained, 
  

   and 
  the 
  abdominal 
  segments 
  are 
  usually 
  

   well 
  developed 
  in 
  these 
  insects. 
  Para- 
  

   nota, 
  or 
  lateral 
  expansions 
  of 
  the 
  tergal 
  

   region 
  (Jour. 
  N.Y. 
  Ent. 
  Soc, 
  vol. 
  24, 
  

   p. 
  1) 
  occur 
  on 
  the 
  abdominal 
  segments, 
  

   particularly 
  those 
  near 
  the 
  end 
  of 
  the 
  

   abdomen, 
  in 
  certain 
  immature 
  Odonata 
  

   and 
  Ephemerida, 
  and 
  are 
  occasionally 
  

   retained 
  on 
  the 
  last 
  abdominal 
  segments 
  

   of 
  the 
  adult 
  also. 
  These 
  and 
  many 
  of 
  

   the 
  characters 
  mentioned 
  above 
  do 
  not 
  

   occur 
  in 
  all 
  of 
  the 
  members 
  of 
  the 
  

   Ephemerid 
  section, 
  nor 
  are 
  they 
  char- 
  

   acteristic 
  of 
  the 
  members 
  of 
  this 
  section 
  

   alone, 
  so 
  that 
  the 
  only 
  character 
  pecuhar 
  to 
  this 
  group 
  of 
  

   insects 
  and 
  occurring 
  in 
  most 
  of 
  its 
  members, 
  is 
  their 
  

   inability 
  to 
  fold 
  their 
  wings 
  flat 
  along 
  the 
  abdomen. 
  

  

  Certain 
  insects 
  belonging 
  to 
  each 
  of 
  the 
  sections 
  men- 
  

   tioned 
  above 
  {i. 
  e. 
  the 
  Ephemerid, 
  Plecopteron, 
  and 
  

   Neuropteron 
  sections) 
  may 
  occupy 
  a 
  position 
  anatomically 
  

   intermediate 
  between 
  the 
  members 
  of 
  their 
  own 
  and 
  of 
  the 
  

   other 
  sections. 
  The 
  three 
  sections 
  may 
  thus 
  have 
  a 
  certain 
  

   amount 
  of 
  " 
  territory 
  " 
  in 
  common, 
  yet 
  each 
  taken 
  

   separately 
  forms 
  a 
  well-defined 
  group 
  in 
  itself. 
  If 
  this 
  

   were 
  to 
  be 
  represented 
  graphically, 
  the 
  three 
  sections 
  

   would 
  be 
  represented 
  as 
  three 
  intersecting 
  circles 
  (Fig. 
  1) 
  

   each 
  of 
  which 
  taken 
  separately 
  forms 
  a 
  distinct 
  well- 
  

   defined 
  division 
  ; 
  yet 
  in 
  the 
  area 
  of 
  overlapping 
  they 
  have 
  

   a 
  certain 
  amount 
  of 
  territory 
  in 
  common. 
  It 
  would 
  perhaps 
  

  

  Fig. 
  1. 
  

  

  