﻿STRUCTURE 
  AND 
  CLASSIFICATION 
  OF 
  THE 
  ARACHNIDA. 
  249 
  

  

  Remarks 
  ou 
  the 
  Aranei\3. 
  — 
  The 
  spiders 
  are 
  the 
  most 
  

   numerous 
  and 
  diversified 
  group 
  of 
  the 
  Arachnida 
  ; 
  about 
  

   2000 
  species 
  are 
  known. 
  No 
  noteworthy 
  fossil 
  spiders 
  are 
  

   known 
  ; 
  the 
  best 
  preserved 
  are 
  in 
  amber 
  of 
  Oligocene 
  age. 
  

   Protolycosa 
  and 
  Arthrolycosa 
  occur 
  in 
  the 
  Carboni- 
  

   ferous. 
  Morphologically 
  the 
  spiders 
  are 
  remarkable 
  for 
  the 
  

   concentration 
  and 
  specialisation 
  of 
  their 
  structure, 
  which 
  is 
  

   accompanied 
  with 
  high 
  physiological 
  efficiency. 
  The 
  larger 
  

  

  Fig. 
  64. 
  — 
  Liphistius 
  desultor. 
  Under 
  side 
  of 
  the 
  uplifted 
  

   genital 
  or 
  first 
  opisthosoniatic 
  somite 
  of 
  the 
  female; 
  g, 
  genital 
  

   aperture; 
  p, 
  pitted 
  plate, 
  probably 
  a 
  gland 
  for 
  the 
  secretion 
  of 
  

   adhesive 
  material 
  for 
  the 
  eggs; 
  I, 
  the 
  edges 
  of 
  the 
  lamellai 
  of 
  the 
  

   lung-books 
  of 
  the 
  first 
  pair. 
  (Original 
  drawing 
  by 
  Pocock.) 
  

  

  species 
  of 
  Bird's-nest 
  Spiders 
  (Avicularia), 
  the 
  opisthosoraa 
  

   of 
  which 
  is 
  as 
  large 
  as 
  a 
  bantam's 
  Q^^, 
  undoubtedly 
  attack 
  

   young 
  birds, 
  and 
  M'Cook 
  gives 
  an 
  account 
  of 
  the 
  capture 
  in 
  

   its 
  web 
  by 
  an 
  ordinary 
  house 
  spider 
  of 
  a 
  small 
  mouse. 
  The 
  

   '^retrovert 
  " 
  or 
  bent-back 
  first 
  pair 
  of 
  appendages 
  is 
  provided 
  

   with 
  a 
  poison 
  gland 
  opening 
  on 
  the 
  fang 
  or 
  terminal 
  segment. 
  

   Spiders 
  form 
  at 
  least 
  two 
  kinds 
  of 
  construction 
  — 
  snares 
  for 
  

   the 
  capture 
  of 
  prey 
  and 
  nests 
  for 
  the 
  preservation 
  of 
  the 
  

   young. 
  The 
  latter 
  are 
  only 
  formed 
  by 
  the 
  female, 
  which 
  is 
  a 
  

   larger 
  and 
  more 
  powerful 
  animal 
  than 
  the 
  male. 
  Like 
  the 
  

   scorpions 
  the 
  spiders 
  have 
  a 
  special 
  tendency 
  to 
  cannibalism, 
  

   and 
  accordingly 
  the 
  male, 
  in 
  approaching 
  the 
  female 
  for 
  the 
  

   purpose 
  of 
  fertilising 
  her, 
  is 
  liable 
  to 
  be 
  fallen 
  upon 
  and 
  

   sucked 
  dry 
  by 
  the 
  object 
  of 
  his 
  attentions. 
  The 
  sperm 
  is 
  

   removed 
  by 
  the 
  male 
  from 
  the 
  genital 
  aperture 
  into 
  a 
  special 
  

   receptacle 
  on 
  the 
  terminal 
  segment 
  of 
  the 
  second 
  prosomatic 
  

   appendage. 
  Thus 
  held 
  out 
  at 
  some 
  distance 
  from 
  the 
  body, 
  

  

  