﻿STRUCTDEE 
  AND 
  CLASSIFICATION 
  OF 
  THE 
  ARACHNIDA. 
  177 
  

  

  the 
  specimen, 
  recently 
  carefully 
  studied 
  by 
  the 
  writer 
  and 
  

   Mr. 
  Pocock, 
  reveals 
  neither 
  gill-bearing- 
  limbs 
  nor 
  stigmata. 
  

   The 
  probability 
  appears 
  to 
  be 
  against 
  an 
  actual 
  introversion 
  

   of 
  the 
  appendage 
  and 
  its 
  lamellae, 
  as 
  was 
  at 
  one 
  time 
  

   suggested 
  by 
  Lankester. 
  It 
  is 
  probable 
  that 
  such 
  an 
  in- 
  

   sinking 
  as 
  is 
  shown 
  in 
  the 
  accompanying 
  diagram 
  has 
  taken 
  

  

  Fig. 
  16.— 
  Diagram 
  to 
  show 
  the 
  way 
  in 
  which 
  an 
  outgrowing 
  gill- 
  

   process 
  bearing 
  l)lood-holding 
  lamellae 
  may 
  give 
  rise, 
  it 
  the 
  sternal 
  

   body-wall 
  sinks 
  inwards, 
  to 
  a 
  lung-chamber 
  with 
  air-holding 
  lamellae. 
  

   I 
  is 
  the 
  embryonic 
  condition 
  ; 
  bs, 
  blood 
  sinus 
  ; 
  L 
  is 
  the 
  condition 
  of 
  

   outgrowth 
  with 
  gl, 
  gill 
  lamellae 
  ; 
  A 
  is 
  tiie 
  condition 
  of 
  in-sinking 
  of 
  

   the 
  sternal 
  surface 
  and 
  consequent 
  enclosure 
  of 
  the 
  lamelligerous 
  

   surface 
  of 
  the 
  appendage 
  in 
  a 
  chamber 
  with 
  narrow 
  orifice 
  — 
  the 
  

   pulmonary 
  air-holding 
  chamber 
  ; 
  pi, 
  pulmonary 
  lamellae 
  ; 
  bs, 
  blood 
  

   sinus. 
  (After 
  Kingsley.) 
  

  

  place 
  (Fig. 
  16) 
  ; 
  but 
  we 
  are 
  yet 
  in 
  need 
  of 
  evidence 
  as 
  to 
  the 
  

   exact 
  equivalence 
  of 
  margins, 
  axis, 
  etc., 
  obtaining 
  between 
  

   the 
  lung-book 
  of 
  Scorpio 
  and 
  the 
  gill-book 
  of 
  Limulus. 
  

   Zoologists 
  are 
  familiar 
  with 
  many 
  instances 
  (fishes, 
  crus- 
  

   taceans) 
  in 
  which 
  the 
  protective 
  walls 
  of 
  a 
  water-breathing 
  

   organ 
  or 
  gill 
  apparatus 
  become 
  converted 
  into 
  an 
  air-breath- 
  

  

  