﻿A 
  STUDY 
  IN 
  CARCINOLOGY. 
  59 
  

  

  sand 
  or 
  other 
  material 
  from 
  beneath 
  the 
  anterior 
  part 
  of 
  the 
  carapace, 
  the 
  

   raking 
  action 
  being 
  facilitated 
  by 
  the 
  five 
  large 
  spines 
  on 
  the 
  lower 
  margin 
  

   of 
  the 
  propodus. 
  Thus 
  a 
  more 
  or 
  less 
  clear 
  water-way 
  is 
  kept 
  on 
  the 
  under 
  

   side 
  of 
  the 
  anterior 
  side 
  of 
  the 
  thorax. 
  

  

  When 
  the 
  ischiomerus 
  is 
  drawn 
  as 
  far 
  back 
  as 
  possible, 
  the 
  carpus 
  can 
  he 
  

   flexed 
  inwards 
  to 
  form 
  an 
  acute 
  angle 
  with 
  it, 
  and 
  the 
  flattened 
  propodus 
  may 
  

   then 
  he 
  folded 
  hack 
  so 
  far 
  that 
  its 
  posterior 
  margin 
  fits 
  into 
  a 
  groove 
  in 
  the 
  

   merus 
  and 
  both 
  it 
  and 
  the 
  dactylus 
  are 
  pressed 
  against 
  the 
  basal 
  joints 
  of 
  

   the 
  third 
  maxillipeds. 
  In 
  this 
  position 
  also 
  the 
  propodus 
  can 
  he 
  rotated 
  

   outwards 
  with 
  a 
  raking 
  action 
  so 
  as 
  to 
  clear 
  away 
  sand 
  from 
  beneath 
  the 
  

   body, 
  without 
  any 
  corresponding 
  movement 
  of 
  the 
  ischiomerus 
  and 
  carpus. 
  

   A 
  close 
  examination 
  of 
  the 
  chelipeds 
  leaves 
  no 
  doubt 
  that 
  their 
  main 
  function 
  

   is 
  to 
  keep 
  open 
  a 
  passage 
  for 
  water 
  down 
  to 
  their 
  basal 
  joints. 
  From 
  this 
  

   point 
  backwards 
  water 
  must 
  pass 
  in 
  two 
  streams 
  to 
  the 
  posterior 
  branchial 
  

   orifices 
  along 
  passages 
  roofed 
  in, 
  partly 
  by 
  the 
  overhanging 
  edges 
  of 
  the 
  

   branchioslegite, 
  partly 
  by 
  the 
  forwardly 
  directed 
  last 
  pair 
  of 
  pereiopods. 
  

   The 
  inner 
  walls 
  of 
  these 
  passages 
  are 
  formed 
  by 
  theepimera 
  of 
  the 
  eleventh, 
  

   twelfth, 
  and 
  thirteenth 
  segments, 
  which 
  are 
  somewhat 
  excavated 
  and 
  over- 
  

   hung 
  by 
  the 
  edge 
  of 
  the 
  hranchiostegites. 
  Their 
  outer 
  walls 
  are 
  formed 
  by 
  

   the 
  first 
  three 
  pairs 
  of 
  pereiopods, 
  which 
  are 
  tucked 
  up 
  under 
  the 
  roof 
  formed 
  

   by 
  the 
  last 
  pereiopods, 
  the 
  merus 
  in 
  each 
  case 
  being 
  directed 
  forwards, 
  the 
  

   carpus, 
  propodus, 
  and 
  broad 
  lanceolate 
  dactylus 
  downwards 
  and 
  backwards. 
  

   The 
  segments 
  of 
  the 
  pereiopods 
  being 
  broad 
  and 
  flattened 
  and 
  their 
  margins 
  

   furnished 
  with 
  fringes 
  of 
  stiff 
  closely 
  set 
  hairs, 
  they 
  form 
  a 
  sort 
  of 
  basket- 
  

   work 
  or 
  sieve 
  the 
  meshes 
  of 
  which 
  are 
  tilled 
  in 
  by 
  the 
  fringes 
  of 
  hairs, 
  and 
  the 
  

   whole 
  apparatus 
  is 
  adapted 
  to 
  admit 
  to 
  the 
  interior 
  water 
  from 
  which 
  sand 
  

   and 
  other 
  solid 
  particles 
  have 
  been 
  strained. 
  The 
  strainer 
  is 
  made 
  more 
  

   effective 
  by 
  the 
  dense 
  hairy 
  fringes 
  on 
  the 
  edges 
  of 
  the 
  branchiostegite, 
  and 
  

   the 
  whole 
  apparatus 
  is 
  completed 
  and 
  roofed 
  in 
  posteriorly 
  by 
  the 
  flattened 
  

   segments 
  of 
  the 
  abdomen, 
  which 
  are 
  likewise 
  provided 
  with 
  dense 
  fringes 
  of 
  

   stiff 
  hairs. 
  

  

  Whatever 
  may 
  be 
  the 
  position 
  of 
  the 
  chelipeds, 
  there 
  is 
  a 
  ventral 
  gap 
  on 
  

   either 
  side 
  between 
  their 
  basal 
  joints 
  and 
  the 
  first 
  pair 
  of 
  the 
  pereiopods. 
  

   This 
  gap 
  is 
  partly 
  filled 
  by 
  the 
  " 
  epaulettes 
  " 
  projecting 
  from 
  the 
  sterna 
  of 
  

   the 
  eleventh 
  segment 
  ; 
  the 
  rest 
  of 
  the 
  gap 
  is 
  bridged 
  over 
  by 
  the 
  stiff 
  hairs 
  

   projecting 
  from 
  all 
  round 
  the 
  margins 
  of 
  the 
  epaulettes 
  and 
  forming 
  a 
  very 
  

   effective 
  strainer. 
  It 
  is 
  through 
  these 
  two 
  gaps 
  furnished 
  with 
  this 
  efficient 
  

   straining 
  apparatus 
  that 
  the 
  greater 
  part 
  of 
  the 
  respiratory 
  current 
  of 
  water 
  

   must 
  find 
  its 
  way 
  from 
  the 
  cavity 
  raked 
  out 
  in 
  the 
  sand 
  by 
  the 
  chelipeds 
  

   underneath 
  the 
  anterior 
  part 
  of 
  the 
  thorax. 
  

  

  The 
  structure 
  and 
  arrangement 
  of 
  the 
  pereiopods 
  and 
  their 
  relations 
  

   to 
  the 
  thoracic 
  epimera 
  and 
  abdomen 
  being 
  as 
  above 
  described, 
  it 
  may 
  he 
  

   inferred 
  that 
  Ranina 
  buries 
  itself 
  in 
  the 
  sand 
  by 
  the 
  digging 
  action 
  of 
  the 
  

  

  