﻿28 
  DR. 
  G. 
  C. 
  BOURNE 
  ON 
  THE 
  RANINID.E: 
  

  

  second 
  maxillae 
  are 
  narrow, 
  the 
  inner 
  lobes 
  normal 
  (Ortmann). 
  Finally, 
  as 
  

   I 
  shall 
  show, 
  the 
  nervous 
  system 
  is 
  more 
  Astacuran 
  in 
  type 
  than 
  in 
  any 
  

   other 
  Brachyura. 
  In 
  addition, 
  the 
  Il'ininidse 
  exhibit 
  a 
  number 
  of 
  features 
  

   peculiar 
  to 
  themselves, 
  and 
  these 
  I 
  shall 
  discuss 
  in 
  detail 
  in 
  the 
  later 
  part 
  of 
  

   this 
  paper. 
  

  

  For 
  the 
  present 
  it 
  is 
  only 
  necessary 
  to 
  refer 
  to 
  the 
  theory 
  originally 
  pro- 
  

   pounded 
  by 
  Huxley 
  and 
  brilliantly 
  sustained 
  by 
  Bouvier 
  in 
  his 
  essay, 
  ' 
  Sur 
  

   l'orhiine 
  homarienne 
  dps 
  Orabes' 
  (22), 
  that 
  the 
  crabs 
  are 
  not 
  descended 
  fivm 
  

   Paguridaa 
  nor 
  from 
  Gralatheida? 
  nor 
  Thalassinidre, 
  but 
  directly 
  from 
  the 
  

   Astacura, 
  and 
  in 
  particular 
  from 
  the 
  Homaridaa 
  through 
  the 
  Dromiacea. 
  

   "• 
  Les 
  Dromiaces 
  par 
  l'intermediare 
  des 
  Homolodromies 
  ou 
  de 
  formes 
  tres 
  

   voisines, 
  derivent 
  directement 
  des 
  Homarides 
  juraesiques 
  ou 
  de 
  Homarides 
  

   qui 
  leur 
  ressemblent." 
  Exception 
  being 
  made 
  of 
  such 
  crab-like 
  forms 
  as 
  

   Porcellana, 
  Lithodes, 
  and 
  the 
  P 
  orcellanopagurus 
  recently 
  described 
  by 
  

   Borrodaile, 
  Bouvier's 
  theory 
  of 
  the 
  origin 
  of 
  crabs 
  is 
  now 
  generally 
  accepted, 
  

   and 
  it 
  follows 
  that, 
  if 
  the 
  Raninidse 
  be 
  true 
  crabs, 
  they 
  must 
  be 
  descended 
  

   from 
  a 
  Homarid 
  or 
  Nephropsid 
  ancestor 
  by 
  way 
  of 
  the 
  Dromiacea. 
  Thus 
  

   Bouvier 
  (2k!) 
  has 
  given 
  convincing 
  arguments 
  for 
  the 
  derivation 
  of 
  the 
  

   Dorippidse 
  from 
  the 
  Dromiacea, 
  and 
  Alcock 
  (2) 
  sees 
  in 
  his 
  genus 
  Cymonomops, 
  

   which 
  differs 
  but 
  little 
  from 
  Cyclodorippe, 
  a 
  number 
  of 
  Raninoid 
  characters 
  

   which, 
  he 
  holds, 
  warrant 
  the 
  conclusion 
  that 
  "we 
  have, 
  in 
  fact, 
  in 
  some 
  of 
  

   these 
  deep-sea 
  forms 
  the 
  clearest 
  evidence 
  of 
  the 
  close 
  relation 
  of 
  the 
  Ranina 
  

   to 
  the 
  Dorippe 
  type 
  and 
  quite 
  sufficient 
  justification 
  for 
  accepting 
  de 
  Haan's 
  

   scheme 
  of 
  the 
  Oxystomata, 
  almost 
  without 
  modification/' 
  Cymonomops, 
  

   however, 
  is 
  clearly 
  a 
  highly-specialised 
  Cyclodorippid 
  ; 
  it 
  has 
  been 
  placed 
  in 
  

   this 
  family 
  by 
  Bouvier, 
  and 
  its 
  supposed 
  resemblances 
  to 
  the 
  Raninidae 
  are 
  

   of 
  the 
  most 
  superficial 
  character. 
  If 
  the 
  last-named 
  family 
  were 
  descended 
  

   from 
  the 
  Dromiacea 
  it 
  would 
  hardly 
  be 
  through 
  a 
  Dorippid 
  line, 
  but 
  it 
  is 
  my 
  

   object 
  to 
  show 
  in 
  the 
  following 
  pages 
  that 
  the 
  Raninidae, 
  though 
  by 
  defini- 
  

   tion 
  they 
  must 
  still 
  be 
  included 
  among 
  the 
  crabs, 
  are 
  not 
  derived 
  from 
  a 
  

   Dromiid 
  ancestor, 
  but 
  have 
  been 
  evolved 
  as 
  an 
  independent 
  group 
  from 
  the 
  

   Astacura. 
  In 
  sustaining 
  this 
  thesis 
  1 
  shall 
  place 
  reliance 
  first 
  of 
  all 
  on 
  the 
  

   nervous 
  system, 
  and 
  secondly 
  on 
  the 
  character 
  and 
  degree 
  of 
  development 
  

   of 
  the 
  endophragmal 
  skeleton. 
  

  

  Our 
  knowledge 
  of 
  the 
  nervous 
  system 
  of 
  the 
  Decapoda 
  i-* 
  not 
  very 
  exten- 
  

   sive, 
  and 
  what 
  we 
  do 
  know 
  is 
  due 
  largely 
  to 
  the 
  researches 
  of 
  Bouvier 
  (21). 
  

   He 
  has 
  demonstrated 
  that 
  the 
  degree 
  of 
  concentration 
  of 
  the 
  nervous 
  system 
  

   varies 
  so 
  considerably 
  in 
  the 
  several 
  groups 
  of 
  Decapoda 
  reptantia 
  that 
  it 
  

   cannot 
  of 
  itself 
  be 
  taken 
  as 
  a 
  sure 
  guide 
  of 
  affinity, 
  but 
  I 
  shall 
  be 
  content 
  

   to 
  found 
  my 
  argument 
  upon 
  a 
  sentence 
  taken 
  from 
  his 
  essay, 
  i 
  Sur 
  l'origine 
  

   homarienne 
  des 
  Crabes.' 
  " 
  Le 
  systeme 
  nerveux 
  des 
  Crustaces 
  decapodes, 
  en 
  

   effet, 
  subit 
  une 
  concentration 
  longitudinale 
  reguliere 
  a 
  mesurequ'on 
  d'eloigne 
  

  

  