﻿60 
  DR. 
  G. 
  C. 
  BOURNE 
  ON 
  THE 
  RANJNID^ 
  : 
  

  

  first 
  three 
  pairs 
  of 
  pereiopods, 
  the 
  fourth 
  pair 
  being 
  used 
  to 
  shovel 
  the 
  dis- 
  

   placed 
  sand 
  outwards. 
  When 
  dug 
  in, 
  the 
  animal 
  may 
  be 
  inferred 
  to 
  assume 
  

   an 
  oblique 
  position, 
  the 
  frontal 
  spines 
  of 
  the 
  carapace 
  just 
  breaking 
  the 
  

   surface 
  of 
  the 
  sand 
  ; 
  the 
  chelipeds 
  are 
  folded 
  up 
  under 
  the 
  pterygostomial 
  

   region 
  of 
  the 
  carapace 
  and 
  the 
  long 
  three-jointed 
  eye-stalks 
  maybe 
  extended 
  

   well 
  above 
  the 
  sand 
  on 
  the 
  look-out 
  or, 
  on 
  the 
  approach 
  of 
  danger, 
  may 
  

   be 
  folded 
  back 
  and 
  concealed 
  in 
  the 
  orbital 
  cavities. 
  In 
  this 
  position 
  the 
  

   normal 
  respiratory 
  current 
  will 
  be 
  provided 
  for 
  by 
  the 
  raking 
  action 
  of 
  

   the 
  chelipeds 
  and 
  the 
  lateral 
  water- 
  passages 
  enclosed 
  between 
  the 
  

   pereiopods 
  and 
  the 
  thoracic 
  epimera, 
  as 
  described 
  above. 
  These 
  afford 
  a 
  

   mechanism 
  whereby 
  filtered 
  water 
  is 
  supplied 
  to 
  the 
  posterior 
  branched 
  

   openings, 
  and 
  the 
  normal 
  exhalant 
  current 
  will 
  pass 
  out 
  by 
  the 
  narrow 
  

   anterior 
  passage 
  bounded 
  below 
  by 
  the 
  merus 
  of 
  the 
  third 
  maxilliped 
  and 
  

   laterally 
  by 
  the 
  flattened 
  basal 
  joints 
  of 
  the 
  second 
  antennae. 
  

  

  As 
  the 
  Raninidac 
  are 
  tropical 
  and 
  sub-tropical 
  crabs 
  living 
  at 
  considerable 
  

   depths 
  it 
  has 
  not 
  been 
  possible 
  for 
  me 
  to 
  observe 
  the 
  habits 
  of 
  the 
  living 
  

   animals, 
  much 
  less 
  to 
  make 
  experiments 
  on 
  their 
  respiratory 
  mechanisms. 
  

   But 
  in 
  the 
  absence 
  of 
  direct 
  evidence 
  I 
  consider 
  myself 
  justified 
  in 
  giving 
  

   the 
  foregoing 
  account 
  of 
  the 
  course 
  of 
  the 
  normal 
  respiratory 
  current, 
  the 
  

   more 
  so 
  because 
  an 
  examination 
  of 
  numerous 
  specimens 
  of 
  Kotopoides 
  latus 
  

   and 
  of 
  several 
  examples 
  of 
  Zanclifer 
  caribensis 
  in 
  the 
  British 
  Museum 
  of 
  

   Natural 
  History 
  gives 
  the 
  clearest 
  evidence 
  that 
  these 
  species 
  are 
  sand 
  

   bui 
  rowers, 
  and 
  that 
  an 
  inhalant 
  current 
  passes 
  into 
  their 
  branchial 
  chambers 
  

   through 
  the 
  posterior 
  branchial 
  orifices, 
  which 
  are 
  exceptionnlly 
  large 
  and 
  

   conspicuous 
  in 
  these 
  cases. 
  In 
  nearly 
  all 
  the 
  individuals 
  of 
  these 
  two 
  species 
  

   the 
  conspicuous 
  hairy 
  fringes 
  of 
  the 
  pereiopods, 
  of 
  the 
  abdominal 
  pleura, 
  of 
  

   the 
  edges 
  of 
  the 
  branchiostegite, 
  and 
  of 
  the 
  epaulettes 
  of 
  the 
  eleventh 
  sterna, 
  

   are 
  more 
  or 
  less 
  heavily 
  clogged 
  with 
  sand, 
  a 
  fact 
  which 
  bears 
  witness 
  to 
  

   their 
  function 
  as 
  a 
  filtering 
  apparatus. 
  On 
  the 
  other 
  hand, 
  the 
  water- 
  

   passages 
  lying 
  between 
  the 
  posterior 
  thoracic 
  epimera 
  and 
  the 
  pereiopods, 
  

   and 
  therefore 
  guarded 
  by 
  these 
  hairy 
  fringes, 
  are 
  remarkably 
  clean 
  and 
  free 
  

   from 
  sand. 
  The 
  filtration, 
  however, 
  has 
  not 
  been 
  perfect, 
  for 
  the 
  walls 
  of 
  

   the 
  posterior 
  branchial 
  passages 
  are 
  encrusted 
  with 
  fine 
  particles 
  of 
  sand, 
  

   the 
  distribution 
  of 
  which 
  leaves 
  no 
  doubt 
  that 
  the 
  current 
  which 
  deposited 
  

   them 
  set 
  in 
  from 
  behind 
  forwards. 
  The 
  evidence 
  in 
  these 
  two 
  species 
  is 
  

   remarkably 
  clear, 
  and 
  the 
  inferences 
  drawn 
  from 
  it 
  may 
  be 
  extended 
  to 
  

   JS 
  T 
  otopus 
  dorsipes 
  and 
  to 
  Notosccles 
  cltimmonis, 
  though, 
  in 
  the 
  last-named 
  

   species, 
  in 
  which 
  the 
  last 
  pair 
  of 
  pereiopods 
  are 
  greatly 
  reduced 
  in 
  size, 
  there 
  

   is 
  evidence 
  that 
  the 
  posterior 
  inhalant 
  respiratory 
  current 
  is 
  becoming 
  of 
  less 
  

   importance 
  and 
  that 
  the 
  incurrent 
  supply 
  of 
  water 
  to 
  the 
  branchial 
  chamber 
  

   is 
  chiefly 
  provided 
  for 
  by 
  special 
  modifications 
  of 
  the 
  antennary 
  region. 
  

   In 
  the 
  absence 
  of 
  opportunities 
  for 
  observation 
  of 
  and 
  experiment 
  on 
  living 
  

  

  