﻿Diptera, 
  Hemiptera 
  and 
  Insects 
  related 
  to 
  Neuroptera. 
  107 
  

  

  lateral 
  cervical 
  plates 
  " 
  ; 
  but 
  in 
  certain 
  other 
  respects, 
  the 
  

   sawfly 
  larvae 
  are 
  more 
  similar 
  to 
  Lepidopterous 
  larvae. 
  

  

  The 
  venation 
  of 
  the 
  wings 
  of 
  certain 
  sawflies, 
  particularly 
  

   in 
  the 
  anal 
  region, 
  is 
  strongly 
  suggestive 
  of 
  the 
  condition 
  

   occurring 
  in 
  the 
  wings 
  of 
  some 
  of 
  the 
  more 
  primitive 
  

   Psocidae, 
  and 
  I 
  find 
  indications 
  of 
  a 
  relationship 
  between 
  

   the 
  two 
  in 
  certain 
  features 
  of 
  the 
  head 
  and 
  thorax 
  (especially 
  

   the 
  tergal 
  region). 
  On 
  the 
  other 
  hand, 
  the 
  nature 
  of 
  the 
  

   male 
  genitaha 
  of 
  the 
  sawflies 
  is 
  surprisingly 
  like 
  the 
  geni- 
  

   talia 
  of 
  male 
  Mecoptera, 
  the 
  shape 
  of 
  the 
  head 
  and 
  the 
  

   nature 
  of 
  the 
  mouthparts, 
  etc., 
  are 
  much 
  more 
  similar 
  in 
  

   the 
  sawflies 
  and 
  Mecoptera, 
  and 
  on 
  the 
  whole 
  the 
  closest 
  

   affinities 
  of 
  the 
  Hymenoptera 
  appear 
  to 
  be 
  with 
  the 
  Meco- 
  

   ptera 
  and 
  other 
  insects 
  grouped 
  about 
  the 
  Neuroptera. 
  I 
  

   have 
  therefore 
  represented 
  the 
  Hymenoptera 
  in 
  the 
  

   diagram 
  as 
  a 
  very 
  primitive 
  group 
  occupying 
  a 
  position 
  

   somewhat 
  intermediate 
  between 
  the 
  insects 
  grouped 
  about 
  

   the 
  Psocidae 
  and 
  those 
  grouped 
  about 
  the 
  Neuroptera, 
  

   with 
  their 
  strongest 
  affinities 
  on 
  the 
  side 
  of 
  the 
  Neuro- 
  

   pteroid 
  forms 
  such 
  as 
  the 
  Mecoptera. 
  The 
  similarity 
  

   between 
  the 
  wing 
  veins 
  of 
  the 
  Diptera 
  and 
  sawflies 
  pointed 
  

   out 
  by 
  MacGilhvray, 
  1906 
  (Proc. 
  U.S. 
  Nat. 
  Museum, 
  29), 
  

   and 
  others 
  would 
  thus 
  be 
  readily 
  explained 
  by 
  the 
  fact 
  

   that 
  Diptera 
  are 
  descended 
  from 
  Mecoptera-like 
  forbears, 
  

   and 
  if 
  the 
  sawflies 
  resemble 
  Mecoptera, 
  they 
  would 
  naturally 
  

   be 
  similar 
  in 
  some 
  respects 
  to 
  the 
  Diptera 
  also. 
  In 
  the 
  

   same 
  way, 
  the 
  resemblances 
  between 
  the 
  Hymenoptera 
  

   and 
  the 
  Trichoptera 
  or 
  Lepidoptera 
  might 
  be 
  explained 
  as 
  

   the 
  result 
  of 
  their 
  mutual 
  relationship 
  to 
  the 
  Mecoptera. 
  

   In 
  some 
  respects 
  the 
  Hymenoptera 
  are 
  quite 
  hke 
  the 
  

   Neuroptera, 
  and 
  the 
  latter 
  group 
  may 
  possibly 
  represent 
  

   the 
  ancestral 
  forms 
  from 
  which 
  the 
  Hymenoptera 
  were 
  

   derived 
  ; 
  but 
  it 
  is 
  more 
  probable 
  that 
  the 
  ancestors 
  of 
  the 
  

   Hymenoptera 
  were 
  very 
  primitive 
  forms 
  occupying 
  a 
  

   position 
  intermediate 
  between 
  the 
  Neuroptera 
  and 
  the 
  

   Psocidae. 
  

  

  Most 
  modern 
  investigators 
  agree 
  in 
  regarding 
  the 
  

   Siphonaptera, 
  Suctoria, 
  or 
  Aphaniptera 
  as 
  the 
  descendants 
  

   of 
  forms 
  very 
  like 
  the 
  Diptera; 
  and 
  their 
  ancestors 
  were 
  

   probably 
  quite 
  similar 
  to 
  the 
  Dipteron 
  family 
  Phoridae. 
  

   The 
  Siphonaptera 
  have 
  therefore 
  been 
  represented 
  in 
  the 
  

   diagram 
  as 
  a 
  lateral 
  branch 
  of 
  the 
  main 
  Dipteron 
  line 
  of 
  

   development, 
  although 
  as 
  Packard, 
  1895 
  (Proc. 
  Boston 
  

   Soc. 
  Nat. 
  Hist., 
  26, 
  p. 
  354), 
  states, 
  " 
  they 
  must 
  have 
  

  

  