﻿STKUCTUEE 
  AND 
  CLASSIFICATION 
  OF 
  THE 
  AL'ACHNIDA. 
  227 
  

  

  ence 
  to 
  tlie 
  condition 
  of 
  the 
  respiratory 
  organs 
  as 
  adapted 
  to 
  

   aquatic 
  or 
  terrestrial 
  life. 
  

  

  Grade 
  a 
  (of 
  the 
  Euaracliuida). 
  Delgbeanchia 
  

   (Hydropneustea) 
  . 
  

  

  Mesosomatic 
  segments 
  furnished 
  with 
  large 
  plate-like 
  

   appendages^ 
  the 
  first 
  pair 
  acting 
  as 
  the 
  genital 
  operculum. 
  

  

  ilG. 
  44. 
  — 
  Dorsal 
  view 
  of 
  Limulus 
  polyphemus, 
  Lim. 
  One 
  

   fourtli 
  tlie 
  Natural 
  size, 
  linear. 
  (From 
  Parker 
  and 
  Haswell, 
  'Text- 
  

   book 
  of 
  Zoology,' 
  after 
  Leuckart.) 
  

  

  the 
  remaining 
  pairs 
  being 
  provided 
  with 
  branchial 
  lamellge 
  

   fitted 
  for 
  breathing 
  oxygen 
  dissclved 
  in 
  water. 
  The 
  praj- 
  

   genital 
  somite 
  partially 
  or 
  wholly 
  obliterated 
  in 
  the 
  adult. 
  

   The 
  mouth 
  lying 
  far 
  back, 
  so 
  that 
  the 
  basal 
  segments 
  of 
  all 
  

   the 
  prosomatic 
  appendages, 
  excepting 
  those 
  of 
  the 
  first 
  pair, 
  

  

  