﻿A 
  STUDY 
  IN 
  CARCINOLOGY. 
  43 
  

  

  Correlated 
  with 
  these 
  modifications 
  is 
  the 
  extent 
  to 
  which 
  the 
  epiinera 
  o£ 
  

   the 
  post-oral 
  segments 
  are 
  involved 
  in 
  the 
  branchiostegal 
  fold. 
  In 
  most 
  

   of 
  the 
  Brachyura 
  that 
  I 
  have 
  examined 
  they 
  are 
  more 
  intimately 
  involved 
  

   than 
  is 
  the 
  case 
  either 
  in 
  the 
  Raninidse 
  or 
  in 
  the 
  Dromiacea, 
  and 
  the 
  corre- 
  

   sponding 
  sterna 
  and 
  artbrophragms 
  are 
  modified 
  and 
  exhibit 
  features 
  

   departing 
  more 
  widely 
  from 
  the 
  Astacuran 
  type. 
  A 
  preliminary 
  Burvey 
  

   leads 
  me 
  to 
  believe 
  that 
  a 
  study 
  of 
  the 
  structure 
  and 
  relations 
  of 
  the 
  first 
  six: 
  

   post-oral 
  segments 
  in 
  the 
  Brachyura 
  will 
  yield 
  results 
  of 
  considerable 
  classi- 
  

   ficatory 
  value, 
  but, 
  any 
  attempt 
  to 
  discuss 
  the 
  subject 
  would 
  involve 
  a 
  long 
  

   digression, 
  and 
  it 
  cannot 
  be 
  pursued 
  any 
  further 
  in 
  this 
  place. 
  

  

  But, 
  before 
  instituting 
  a 
  comparison 
  between 
  the 
  pre-oral 
  sternites 
  and 
  the 
  

   adjacent 
  parts 
  of 
  the 
  exoskeleton 
  in 
  the 
  Dromiacea 
  and 
  Raninidse, 
  it 
  will 
  be 
  

   necessary 
  to 
  make 
  a 
  considerable 
  digression 
  with 
  the 
  purpose 
  of 
  clearing 
  up 
  

   doubtful 
  points 
  in 
  the 
  morphology 
  of 
  this 
  region 
  in 
  the 
  Decapoda 
  reptantia, 
  

   and 
  defining 
  more 
  precisely 
  certain 
  terms 
  which, 
  to 
  say 
  the 
  best 
  of 
  it, 
  are 
  

   used 
  in 
  an 
  ambiguous 
  sense 
  by 
  carcinologists. 
  

  

  In 
  the 
  Astacura 
  and 
  in 
  Brachyura 
  in 
  general 
  there 
  is 
  in 
  front 
  of 
  the 
  mouth 
  

   a 
  plate, 
  usually 
  of 
  considerable 
  breadth 
  laterally, 
  but 
  of 
  variable 
  extent 
  antero- 
  

   posteriorly, 
  to 
  which 
  is 
  given 
  the 
  name 
  of 
  " 
  rpistome." 
  Behind 
  this 
  is 
  the 
  

   triangular, 
  or 
  in 
  Brachyura 
  the 
  more 
  often 
  quadrilateral 
  area 
  known 
  as 
  the 
  

   '"mouth-frame." 
  The 
  confusion 
  arising 
  from 
  the 
  loose 
  application 
  of 
  these 
  

   names 
  is 
  really 
  remarkable. 
  They 
  are 
  due 
  to 
  Milne 
  Edwards 
  and 
  Audouin, 
  

   and 
  it 
  will 
  be 
  well 
  to 
  quote 
  the 
  former 
  author 
  in 
  extenso 
  (25. 
  vol. 
  i. 
  p. 
  251): 
  

   " 
  En 
  arriere 
  des 
  fossettes 
  antennaires, 
  on 
  voit 
  une 
  surface 
  plane, 
  plus 
  ou 
  

   moins 
  etendue, 
  qui 
  represente 
  le 
  troisicme 
  anneau 
  cephalique 
  et 
  qui 
  poste 
  le 
  

   nom 
  d'dpistome. 
  L'espace 
  occupe 
  par 
  l'epistome, 
  les 
  fossettes 
  antennaires 
  et 
  

   la 
  base 
  des 
  antennes 
  externes 
  constituo 
  ce 
  que 
  nous 
  appelons 
  la 
  region 
  

  

  antennaire 
  Les 
  parties 
  laterales 
  et 
  inferieures 
  de 
  la 
  carapace, 
  que 
  

  

  nous 
  appellerons 
  regions 
  pterygostomiennes, 
  sont 
  toujours 
  dirigees 
  plus 
  ou 
  

   moins 
  obliquement 
  en 
  dehors 
  et 
  en 
  haut, 
  et 
  sur 
  la 
  ligne 
  mediane 
  elles 
  laissent 
  

   entre 
  elles 
  un 
  espace 
  vide 
  qui 
  est 
  occupe 
  par 
  l'appareil 
  masticateur 
  et 
  que 
  

   nous 
  designerons 
  sous 
  le 
  nom 
  de 
  cadre 
  buccal 
  ; 
  tan 
  tot 
  ce 
  cadre 
  buccal 
  a 
  la 
  

   forme 
  d'un 
  quadrilatere 
  assez 
  regulier, 
  tantot 
  il 
  est 
  triangulaire, 
  et 
  c'est 
  

   toujours 
  a 
  sa 
  partie 
  anterieure 
  que 
  viennent 
  se 
  terminer 
  les 
  conduits 
  efferens 
  

   des 
  cavites 
  branchiales." 
  The 
  definition 
  of 
  the 
  " 
  epistome 
  " 
  is 
  sufficiently 
  

   exact 
  ; 
  it 
  represents 
  the 
  sternum 
  of 
  the 
  third 
  cephalic 
  segment, 
  that 
  is, 
  the 
  

   antennary 
  segment. 
  Huxley 
  (38) 
  calls 
  the 
  epistome 
  "the 
  sternal 
  region 
  

   which 
  appertains, 
  in 
  part, 
  to 
  the 
  antennae 
  and, 
  in 
  part, 
  to 
  the 
  mandibles." 
  

   He 
  was 
  correct 
  in 
  recognising 
  the 
  inclusion 
  of 
  the 
  mandibular 
  sternal 
  

   element 
  in 
  the 
  "epistome," 
  so 
  we 
  must 
  take 
  the 
  term 
  to 
  connote 
  the 
  con- 
  

   joined 
  antennary 
  and 
  mandibular 
  sterna. 
  Both 
  Milne 
  Edwards 
  and 
  Huxley 
  

   further 
  recognised 
  the 
  distinctness 
  of 
  the 
  antennulary 
  sternum 
  lying 
  in 
  front 
  

  

  