﻿188 
  • 
  : 
  E. 
  RAY 
  LANKESTER. 
  

  

  fused 
  in 
  this 
  region, 
  but 
  there 
  is 
  no 
  embi-yological 
  evidence 
  

   at 
  present 
  which 
  justifies 
  us 
  in 
  assuming 
  the 
  existence 
  iu 
  

   Arachnids 
  of 
  more 
  than 
  two 
  prosthomeres. 
  The 
  position 
  of 
  

   the 
  chelicerae 
  of 
  Limulus, 
  and 
  of 
  the 
  ganglionic 
  nerve-masses 
  

   from 
  which 
  they 
  receive 
  their 
  nerve-supply, 
  is 
  closely 
  similar 
  

   to 
  that 
  of 
  the 
  same 
  structures 
  in 
  Scorpio. 
  The 
  cerebral 
  mass 
  

   is 
  in 
  Limulus 
  more 
  easily 
  separated 
  by 
  dissection 
  as 
  a 
  median 
  

   lobe 
  distinct 
  from 
  the 
  laterally 
  placed 
  ganglia 
  of 
  the 
  cheli- 
  

   ceral 
  somite 
  than 
  is 
  the 
  case 
  in 
  Scorpio, 
  but 
  the 
  relations 
  are 
  

   practically 
  the 
  same 
  in 
  the 
  two 
  forms. 
  Formerly 
  it 
  was 
  

   supposed 
  that 
  in 
  Limulus 
  both 
  the 
  cheliceras 
  and 
  the 
  next 
  

   following 
  pair 
  of 
  appendages 
  were 
  prosthomerous, 
  as 
  in 
  

   Crustacea 
  ; 
  but 
  the 
  dissections 
  of 
  Alphonse 
  Milne-Edwards 
  (6) 
  

   demonstrated 
  the 
  true 
  limitations 
  of 
  the 
  cerebrum, 
  whilst 
  

   embryological 
  researches 
  have 
  done 
  as 
  much 
  for 
  Scorpio. 
  

   Limulus 
  thus 
  agrees 
  with 
  Scorpio 
  and 
  differs 
  from 
  the 
  

   Crustacea, 
  iu 
  which 
  there 
  are 
  three 
  prosthomeres 
  — 
  one 
  ocular 
  

   and 
  two 
  carrying 
  palpiform 
  appendages. 
  It 
  is 
  true 
  that 
  in 
  

   the 
  lower 
  Crustacea 
  (Apus, 
  etc.) 
  we 
  have 
  evidence 
  of 
  the 
  

   gradual 
  movement 
  forward 
  of 
  the 
  nerve-ganglia 
  belonging 
  to 
  

   these 
  palpiform 
  appendages. 
  But 
  although 
  in 
  such 
  lower 
  

   Crustacea 
  the 
  nerve-ganglia 
  of 
  the 
  third 
  prosthomere 
  have 
  

   not 
  fused 
  with 
  the 
  anterior 
  nerve-mass, 
  there 
  is 
  no 
  question 
  

   as 
  to 
  the 
  prajoral 
  position 
  o£ 
  the 
  two 
  appendage-bearing 
  

   somites 
  in 
  addition 
  to 
  the 
  ocular 
  prosthomere. 
  The 
  Crus- 
  

   tacea 
  have, 
  in 
  fact, 
  three 
  prosthomeres 
  in 
  the 
  head 
  and 
  the 
  

   Arachnida 
  only 
  two, 
  and 
  Limulus 
  agrees 
  with 
  the 
  Arachnida 
  

   in 
  this 
  respect, 
  and 
  differs 
  from 
  the 
  Crustacea. 
  The 
  central 
  

   nervous 
  systems 
  of 
  Limulus 
  and 
  of 
  Scorpio 
  present 
  closer 
  

   agreement 
  in 
  structure 
  than 
  can 
  be 
  found 
  when 
  a 
  crustacean 
  is 
  

   compared 
  with 
  either. 
  The 
  wide 
  divarication 
  of 
  the 
  lateral 
  

   cords 
  in 
  the 
  prosoma 
  and 
  their 
  connection 
  by 
  transverse 
  com- 
  

   missures, 
  together 
  with 
  the 
  " 
  attraction 
  " 
  of 
  ganglia 
  to 
  the 
  

   prosomatic 
  ganglion 
  group 
  which 
  properly 
  belong 
  to 
  hinder 
  

   segments, 
  are 
  very 
  nearly 
  identical 
  in 
  the 
  two 
  animals. 
  The 
  

   form 
  and 
  disposition 
  of 
  the 
  ganglion 
  cells 
  are 
  also 
  peculiar 
  

   and 
  closely 
  similar 
  in 
  the 
  two. 
  (See 
  Patten 
  [42] 
  for 
  import- 
  

  

  