﻿STKUCTUKE 
  AND 
  CLASSIFICATION 
  OF 
  'J 
  BE 
  AKACHNIDA. 
  263 
  

  

  four 
  of 
  these 
  furnished 
  with 
  a 
  single 
  pair 
  of 
  dorsally-placed 
  

   spiracles 
  or 
  tracheal 
  stigmata. 
  

  

  Family 
  Opilioacarida? 
  (Opilioacarus). 
  

  

  Sub-order 
  h. 
  Cryptostigmata. 
  — 
  Integument 
  hard, 
  

  

  Fig. 
  78. 
  — 
  Holothyrus 
  nitidissimus, 
  one 
  of 
  the 
  Acari 
  ; 
  after 
  

   Thorell. 
  Enlarged 
  ten 
  times 
  linear. 
  A, 
  lateral 
  view 
  with 
  

   appendages 
  III 
  to 
  VI 
  removed 
  ; 
  1, 
  plate 
  covering 
  the 
  whole 
  dorsal 
  

   area, 
  representing 
  the 
  fused 
  tergal 
  sclerites 
  of 
  the 
  prosoma 
  and 
  

   opisthosoma; 
  2, 
  similarly 
  formed 
  ventral 
  plate; 
  3, 
  tracheal 
  stigma. 
  

  

  B, 
  dorsal 
  view 
  of 
  the 
  same 
  animal 
  ; 
  II 
  to 
  VI, 
  second 
  to 
  sixtii 
  pairs 
  

   of 
  appendages. 
  Tiie 
  first 
  pair 
  of 
  appendages, 
  both 
  in 
  this 
  and 
  in 
  

  

  C, 
  are 
  retracted. 
  C, 
  ventral 
  view 
  of 
  the 
  same; 
  II 
  to 
  VI 
  as 
  in 
  B; 
  

   a, 
  genital 
  orifice 
  ; 
  b, 
  anus 
  ; 
  c, 
  united 
  basal 
  segments 
  of 
  the 
  second 
  

   pair 
  of 
  a])pendages; 
  d, 
  basal 
  segment 
  of 
  the 
  sixth 
  prosomatic 
  

   appendage 
  of 
  the 
  right 
  side. 
  The 
  rest 
  of 
  the 
  appendage, 
  as 
  also 
  of 
  

   appendages 
  III, 
  IV, 
  and 
  V, 
  has 
  been 
  cut 
  away. 
  (Original 
  drawing 
  

   by 
  Pocock 
  and 
  Pickard-Cambridge.) 
  

  

  strengthened 
  by 
  a 
  continuously 
  cbitinised 
  dorsal 
  and 
  ventral 
  

   sclerite. 
  Tracheae 
  typically 
  opening 
  by 
  stigmata 
  situated 
  in 
  

   the 
  articular 
  sockets 
  (acetabula) 
  of 
  the 
  third, 
  fourth, 
  fifth 
  

   and 
  sixth 
  pairs 
  of 
  appendages. 
  

  

  Family 
  Oribatidee 
  (Oribata, 
  Nothrus, 
  Hoplophora). 
  

  

  Sub-order 
  c. 
  Metastigmat 
  a. 
  — 
  Integument 
  mostly 
  like 
  that 
  

  

  