﻿196 
  E. 
  RAY 
  LANKESTER. 
  

  

  cords 
  pass 
  (Figs. 
  3 
  and 
  4, 
  snj)) 
  , 
  and 
  further 
  a 
  dorsal 
  gastric 
  

   canal 
  and 
  arterial 
  canal 
  which 
  transmit 
  the 
  alimentary 
  

   tract 
  and 
  the 
  dorsal 
  artery 
  respectively 
  (Figs. 
  3 
  and 
  4, 
  GO, 
  

   DR). 
  

  

  In 
  LimuluB 
  small 
  entosternites 
  are 
  found 
  in 
  each 
  somite 
  of 
  

   the 
  appendage-bearing 
  mesosoma, 
  and 
  we 
  find 
  in 
  Scorpio, 
  in 
  

   the 
  only 
  somite 
  of 
  the 
  mesosoma 
  which 
  has 
  a 
  well-developed 
  

   pair 
  of 
  appendages, 
  that 
  of 
  the 
  pectens, 
  a 
  small 
  entosternite 
  

   with 
  ten 
  pairs 
  of 
  muscles 
  inserted 
  into 
  it. 
  The 
  supra-pectinal 
  

   entosternite 
  lies 
  ventrad 
  of 
  the 
  nerve-cords. 
  

  

  In 
  Mygale 
  (Figs. 
  5 
  and 
  G) 
  the 
  form 
  of 
  the 
  entosternite 
  is 
  

   more 
  like 
  that 
  of 
  Limulus 
  than 
  is 
  that 
  of 
  Scorpio. 
  The 
  

   anterior 
  notch 
  Ph.N. 
  is 
  similar 
  to 
  that 
  in 
  Limulus, 
  and 
  the 
  

   pairs 
  of 
  upstanding 
  tendons 
  correspond 
  to 
  the 
  similar 
  pairs 
  

   in 
  Limulus, 
  whilst 
  the 
  imbricate 
  triangular 
  pieces 
  of 
  the 
  

   posterior 
  median 
  region 
  resemble 
  the 
  similarly 
  placed 
  struc- 
  

   tures 
  of 
  Limulus 
  in 
  a 
  striking 
  manner. 
  

  

  It 
  must 
  be 
  confessed 
  that 
  we 
  are 
  singularly 
  ignorant 
  as 
  to 
  

   the 
  functional 
  significance 
  of 
  these 
  remarkable 
  organs 
  — 
  the 
  

   entosternites. 
  Their 
  movement 
  in 
  an 
  upward 
  or 
  downward 
  

   direction 
  in 
  Limulus 
  and 
  Mygale 
  must 
  exert 
  a 
  pumping 
  

   action 
  on 
  the 
  blood 
  contained 
  in 
  the 
  dorsal 
  arteries 
  and 
  the 
  

   ventral 
  veins 
  respectively. 
  In 
  Scorpio 
  the 
  completion 
  of 
  the 
  

   horizontal 
  plate 
  by 
  oblique 
  flaps, 
  so 
  as 
  to 
  form 
  an 
  actual 
  

   diaphragm 
  shutting 
  off 
  the 
  cavity 
  of 
  the 
  prosoma 
  from 
  the 
  

   rest 
  of 
  the 
  body, 
  possibly 
  gives 
  to 
  the 
  organs 
  contained 
  in 
  

   the 
  anterior 
  chamber 
  a 
  physiological 
  advantage 
  in 
  respect 
  of 
  

   the 
  supply 
  of 
  arterial 
  blood 
  and 
  its 
  separation 
  from 
  the 
  

   venous 
  blood 
  of 
  the 
  mesosoma. 
  Possibly 
  the 
  movement 
  of 
  

   the 
  diaphragm 
  may 
  determine 
  the 
  passage 
  of 
  air 
  into 
  or 
  out 
  

   of 
  the 
  lung-sacs. 
  Muscular 
  fibres 
  connected 
  with 
  the 
  suc- 
  

   torial 
  pharynx 
  are 
  in 
  Limulus 
  inserted 
  into 
  the 
  entosternite, 
  

   and 
  the 
  activity 
  of 
  the 
  two 
  organs 
  may 
  be 
  correlated. 
  

  

  5. 
  The 
  Blood 
  and 
  the 
  Blood-vascular 
  System. 
  — 
  

   The 
  blood, 
  fluids 
  of 
  Limulus 
  and 
  Scorpio 
  are 
  very 
  similar. 
  

   Not 
  only 
  are 
  the 
  blood-corpuscles 
  of 
  Limulus 
  more 
  like 
  in 
  

   form 
  and 
  granulation 
  to 
  those 
  of 
  Scorpio 
  than 
  to 
  those 
  of 
  

  

  