﻿226 
  E. 
  RAY 
  LANKESTER, 
  

  

  Median 
  eyes 
  are 
  present^ 
  which 
  are 
  monomeriiscons, 
  with 
  dis- 
  

   tinct 
  retinal 
  and 
  corneagenous 
  cell 
  layers, 
  and 
  placed 
  centrally 
  

   on 
  the 
  prosoma. 
  Lateral 
  eyes 
  also 
  may 
  be 
  present, 
  arranged 
  

   in 
  lateral 
  groups, 
  and 
  having 
  a 
  single 
  or 
  double 
  cell 
  layer 
  

   beneath 
  the 
  lens. 
  The 
  first 
  pair 
  of 
  limbs 
  is 
  often 
  chelate 
  or 
  

   prehensile, 
  rarely 
  antenniforni 
  ; 
  whilst 
  the 
  second, 
  third, 
  and 
  

   fourth 
  may 
  also 
  be 
  chelate, 
  or 
  may 
  be 
  simple 
  palps 
  or 
  walking 
  

   legs. 
  

  

  An 
  internal 
  skeletal 
  plate, 
  the 
  so-called 
  "entosternite 
  " 
  of 
  

   fibro-cartilagiuous 
  tissue, 
  to 
  which 
  many 
  muscles 
  are 
  attached, 
  

   is 
  placed 
  between 
  the 
  nerve-cords 
  and 
  the 
  alimentary 
  tract 
  in 
  

   the 
  prosoma 
  of 
  the 
  larger 
  forms 
  (Limulus, 
  Scorpio, 
  My 
  gale). 
  

   In 
  the 
  same 
  and 
  other 
  leading 
  forms 
  a 
  pair 
  of 
  mnch-coiled 
  

   glandular 
  tubes, 
  the 
  coxal 
  glands 
  (coelomocoels 
  in 
  origin), 
  is 
  

   found 
  with 
  a 
  duct 
  opening 
  on 
  the 
  coxa 
  of 
  the 
  fifth 
  pair 
  of 
  

   appendages 
  of 
  the 
  prosoma. 
  The 
  vascular 
  system 
  is 
  highly 
  

   developed 
  (in 
  the 
  non-degenerate 
  forms) 
  ; 
  large 
  arterial 
  

   branches 
  closely 
  accompany 
  or 
  envelop 
  the 
  chief 
  nerves; 
  

   capillaries 
  are 
  well 
  developed. 
  The 
  blood-corpuscles 
  are 
  large 
  

   amoebiform 
  cells, 
  and 
  the 
  blood-plasma 
  is 
  coloured 
  blue 
  by 
  

   hfemocyanin. 
  

  

  The 
  alimentary 
  canal 
  is 
  uncoiled 
  and 
  cylindrical, 
  and 
  gives 
  

   rise 
  laterally 
  to 
  large 
  gastric 
  glands, 
  which 
  are 
  more 
  than 
  a 
  

   single 
  pair 
  in 
  number 
  (two 
  to 
  six 
  pairs), 
  and 
  may 
  assume 
  the 
  

   form 
  of 
  simple 
  caaca. 
  The 
  mouth 
  is 
  minute, 
  and 
  the 
  pharynx 
  

   is 
  always 
  suctorial, 
  never 
  gizzard-like. 
  The 
  gonadial 
  tubes 
  

   (gonoccels 
  or 
  gonadial 
  ccelom) 
  are 
  originally 
  reticular 
  and 
  

   paired, 
  though 
  they 
  may 
  be 
  reduced 
  to 
  a 
  simpler 
  condition. 
  

   They 
  open 
  on 
  the 
  first 
  somite 
  of 
  the 
  mesosoma. 
  In 
  the 
  

   numerous 
  degenerate 
  forms 
  simplification 
  occurs 
  by 
  oblitera- 
  

   tion 
  of 
  the 
  demarcations 
  of 
  somites 
  and 
  the 
  fusion 
  of 
  body- 
  

   regions, 
  together 
  with 
  a 
  gradual 
  suppression 
  of 
  the 
  lamelli- 
  

   ferous 
  respiratory 
  organs 
  and 
  the 
  substitution 
  for 
  them 
  of 
  

   trachea?, 
  which, 
  in 
  their 
  turn, 
  in 
  the 
  smaller 
  and 
  most 
  reduced 
  

   members 
  of 
  the 
  group, 
  may 
  also 
  disappear. 
  

  

  The 
  Euarachnida 
  are 
  divided 
  into 
  two 
  grades 
  with 
  refer- 
  

  

  