﻿STRUCTURE 
  AND 
  CLASSIFICATION 
  OF 
  THll 
  ARACHNIDA. 
  247 
  

  

  ridges, 
  weakly 
  chitinised 
  in 
  the 
  middle. 
  The 
  two 
  pairs 
  of 
  

   spinning 
  appendages 
  retain 
  their 
  primitive 
  position 
  in 
  the 
  

   middle 
  of 
  the 
  lower 
  surface 
  of 
  the 
  opisthosoma 
  far 
  in 
  advance 
  

   of 
  the 
  anus 
  on 
  the 
  third 
  and 
  fourth 
  somites, 
  each 
  appendage 
  

   consisting 
  of 
  a 
  stout, 
  many-jointed 
  outer 
  branch 
  and 
  a 
  

   slender, 
  unsegmented 
  inner 
  branch. 
  Prosoma 
  as 
  in 
  the 
  

   Mygalomorphae, 
  except 
  that 
  the 
  mesosternal 
  area 
  is 
  long 
  and 
  

   narrow. 
  

  

  Family 
  Liphistiidse 
  (Liphistius, 
  ^ 
  Arthrolycosa). 
  

  

  Sub-order 
  b. 
  Opisthothelee 
  (see 
  Fig. 
  63). 
  — 
  Opisthosoma 
  

   without 
  trace 
  of 
  separate 
  terga 
  and 
  sterna, 
  the 
  segmentation 
  

   merely 
  rejDresented 
  posteriorly 
  by 
  slight 
  integumental 
  folds 
  

   and 
  the 
  sterna 
  of 
  the 
  first 
  and 
  second 
  somites 
  by 
  the 
  oper- 
  

   cular 
  plates 
  of 
  the 
  pulmonary 
  sacs. 
  The 
  spinning 
  append- 
  

   ages 
  migrate 
  to 
  the 
  posterior 
  end 
  of 
  the 
  opisthosoma 
  and 
  

   take 
  up 
  a 
  position 
  close 
  to 
  the 
  anus 
  ; 
  the 
  inner 
  branches 
  of 
  

   the 
  anterior 
  pair 
  either 
  atrophy 
  or 
  are 
  represented 
  liomo- 
  

   genetically 
  by 
  a 
  plate, 
  the 
  cribellum, 
  or 
  by 
  an 
  undivided 
  

   membranous 
  lobe, 
  the 
  colulus. 
  

  

  Tribe 
  1. 
  Mygalomorphee. 
  — 
  The 
  plane 
  of 
  the 
  articulation 
  

   of 
  the 
  appendages 
  of 
  the 
  first 
  pair 
  to 
  the 
  prosoma 
  (the 
  

   retrovert) 
  vertical, 
  the 
  basal 
  segment 
  projecting 
  straight 
  

   forwards 
  at 
  its 
  proximal 
  end, 
  the 
  distal 
  segment 
  or 
  fang 
  

   closing 
  backwards 
  in 
  a 
  direction 
  subparallel 
  to 
  the 
  long 
  axis 
  

   of 
  the 
  body. 
  Two 
  pairs 
  of 
  pulmonary 
  sacs. 
  

  

  Families: 
  Theraphosidae 
  (Avicularia, 
  Poecilotheria). 
  

   Barychelidae 
  (Barychelus, 
  Plagiobothrus). 
  Dipluridte 
  

   (Diplura, 
  Macrothele). 
  CtenizidEe 
  (Cteniza, 
  Neme- 
  

   bia). 
  Atypidas 
  (Atypus, 
  Calommata). 
  

  

  Tribe 
  2. 
  Arachnoraorphfe. 
  — 
  The 
  plane 
  of 
  the 
  articulation 
  

   of 
  the 
  appendages 
  of 
  the 
  first 
  pair 
  to 
  the 
  prosoma 
  horizontal, 
  

   the 
  basal 
  segment 
  projecting 
  vertically 
  downwards, 
  at 
  least 
  

   at 
  its 
  proximal 
  end, 
  the 
  distal 
  segment 
  or 
  fang 
  closing 
  

   inwards 
  nearly 
  or 
  quite 
  at 
  right 
  angles 
  to 
  the 
  long 
  axis 
  of 
  

   the 
  body. 
  The 
  posterior 
  pulmonary 
  sacs 
  (except 
  in 
  Hypo- 
  

   chilus) 
  replaced 
  by 
  tracheal 
  tubes; 
  the 
  anterior 
  and 
  pos- 
  

   terior 
  pairs 
  replaced 
  by 
  tracheal 
  tubes 
  in 
  the 
  Caponiidge. 
  

  

  