﻿232 
  E. 
  EAY 
  LANKESTER. 
  

  

  cliel^. 
  Thougli 
  tliere 
  are 
  indications 
  o£ 
  lamelliform 
  respii-atory 
  

   appendages 
  ou 
  mesomatic 
  somites 
  following 
  that 
  bearing 
  the 
  

   genital 
  operculum, 
  we 
  cannot 
  be 
  said 
  to 
  have 
  au}^ 
  proper 
  

   knowledge 
  as 
  to 
  such 
  appendages, 
  and 
  farther 
  evidence 
  

   with 
  regard 
  to 
  them 
  is 
  much 
  to 
  be 
  desired. 
  (For 
  literature 
  

   see 
  Zittel, 
  22^.) 
  

  

  Grade 
  h 
  (of 
  the 
  Euarachnida) 
  . 
  Embolobranchia 
  

   (Aeropneustea). 
  

  

  In 
  primitive 
  forms 
  the 
  respiratory 
  lamella 
  of 
  the 
  append- 
  

   ages 
  of 
  the 
  third, 
  fourth, 
  fifth, 
  and 
  sixth, 
  or 
  of 
  the 
  first 
  and 
  

   second 
  mesosomatic 
  somites 
  are 
  sunk 
  beneath 
  the 
  surface 
  of 
  

   the 
  body, 
  and 
  become 
  adapted 
  to 
  breathe 
  atmospheric 
  oxygen, 
  

   forming 
  the 
  leaves 
  of 
  the 
  so-called 
  lung-books. 
  In 
  specialised 
  

   forms 
  these 
  pulmonary 
  sacs 
  are 
  wholly 
  or 
  partly 
  replaced 
  by 
  

   tracheal 
  tubes. 
  The 
  appendages 
  of 
  the 
  mesosoma 
  generally 
  

   suppressed; 
  in 
  the 
  more 
  primitive 
  forms 
  one 
  or 
  two 
  pairs 
  

   may 
  be 
  retained 
  as 
  organs 
  subservient 
  to 
  reproduction 
  or 
  

   silk-spinning. 
  Mouth 
  situated 
  more 
  forwards 
  than 
  in 
  Delo- 
  

   branchia, 
  no 
  share 
  in 
  mastication 
  being 
  taken 
  by 
  the 
  basal 
  

   segments 
  of 
  the 
  fifth 
  and 
  sixth 
  pairs 
  of 
  prosomatic 
  append- 
  

   ages. 
  Lateral 
  eyes, 
  when 
  present, 
  represented 
  by 
  separate 
  

   ocelli. 
  

  

  The 
  preegenital 
  somite, 
  after 
  appearing 
  in 
  the 
  embryo, 
  

   either 
  is 
  obliterated 
  (Scorpio, 
  Galeodes, 
  Opileo, 
  and 
  others) 
  

   or 
  is 
  retained 
  as 
  a 
  reduced 
  narrow 
  region 
  of 
  the 
  body, 
  the 
  

   " 
  waist," 
  between 
  prosoma 
  and 
  mesosoma. 
  It 
  is 
  represented 
  

   by 
  a 
  full-sized 
  tergal 
  plate 
  in 
  the 
  pseudo-Scorpiones. 
  

  

  Section 
  a. 
  Pectinifera. 
  — 
  The 
  primitive 
  distinction 
  be- 
  

   tween 
  the 
  mesosoma 
  and 
  the 
  metasoma 
  retained, 
  the 
  latter 
  

   consisting 
  of 
  six 
  somites 
  and 
  the 
  former 
  of 
  six 
  somites 
  in 
  the 
  

   adult, 
  each 
  of 
  which 
  is 
  furnished 
  during 
  growth 
  with 
  a 
  pair 
  

   of 
  appendages. 
  Including 
  the 
  prgegenital 
  somite 
  (fig. 
  16), 
  

   which 
  is 
  suppi-essed 
  in 
  the 
  adult, 
  there 
  are 
  thirteen 
  somites 
  

   behind 
  the 
  prosoma. 
  The 
  appendages 
  of 
  the 
  first 
  and 
  second 
  

   mesosomatic 
  somites 
  persisting 
  as 
  the 
  genital 
  operculum 
  and 
  

  

  