﻿A 
  STUDY 
  IN 
  CARCINOLCHiY. 
  63 
  

  

  that 
  in 
  the 
  Etaninidae 
  an 
  anterior 
  incurrent 
  stream 
  of 
  water 
  is 
  produced 
  by 
  

   the 
  "normal" 
  action 
  of 
  the 
  scaphognathito. 
  

  

  In 
  no 
  other 
  member 
  of 
  the 
  group 
  (with 
  the 
  possible 
  exception 
  of 
  Cosmo- 
  

   notus, 
  which 
  I 
  have 
  not 
  had 
  the 
  opportunity 
  of 
  studying 
  sufficiently 
  closely) 
  

   do 
  the 
  flagella 
  of 
  the 
  antenna' 
  form 
  a 
  water-tube 
  as 
  in 
  Wotojms 
  and 
  Ranilia. 
  

   Indeed, 
  the 
  antenna' 
  are 
  modified 
  in 
  other 
  directions 
  but, 
  none 
  the 
  less, 
  are 
  

   subservient 
  to 
  the 
  establishment 
  of 
  an 
  inhalant 
  water 
  current, 
  the 
  course 
  of 
  

   which 
  can 
  best 
  be 
  described 
  by 
  taking 
  Ranina 
  as 
  an 
  example. 
  

  

  In 
  this 
  genus 
  both 
  the 
  antenna 
  1 
  and 
  the 
  antennules 
  are 
  modified 
  in 
  con- 
  

   nection 
  with 
  the 
  respiratory 
  currents. 
  The 
  antenna 
  (figs. 
  35 
  & 
  35 
  a) 
  is 
  short 
  

   and 
  thick, 
  the 
  flagellum 
  reduced 
  to 
  a 
  rudiment 
  comprising 
  at 
  the 
  most 
  seven 
  

   joints 
  ; 
  often 
  it 
  is 
  missing. 
  The 
  two 
  basal 
  joints 
  of 
  the 
  peduncle 
  are 
  fused 
  

   together, 
  but 
  the 
  suture 
  between 
  them 
  remains 
  distinct. 
  The 
  first 
  joint 
  is 
  

   triangular 
  in 
  outline, 
  with 
  the 
  apex 
  directed 
  forward 
  ; 
  its 
  admedian 
  basal 
  

   angle 
  projects 
  inwards 
  and 
  slightly 
  forwards 
  and 
  the 
  excretory 
  aperture 
  is 
  

   placed 
  somewhat 
  to 
  its 
  dorsal 
  side, 
  in 
  such 
  a 
  position 
  that 
  the 
  e 
  xcretory 
  

   products 
  are 
  discharged 
  into 
  the 
  excurrent 
  rather 
  then 
  into 
  the 
  incurrent 
  

   stream. 
  The 
  two 
  basal 
  joints, 
  which 
  have 
  a 
  very 
  limited 
  movement 
  in 
  the 
  

   antennary 
  socket, 
  lie 
  directly 
  in 
  front 
  of 
  the 
  sub-antennary 
  lobe 
  of 
  the 
  

   pterygostome, 
  but 
  the 
  third 
  peduncular 
  segment 
  is 
  flexed 
  inwards 
  to 
  form 
  a 
  

   somewhat 
  acute 
  angle 
  with 
  them. 
  The 
  shape 
  of 
  the 
  third 
  segment 
  can 
  best 
  

   he 
  understood 
  by 
  reference 
  to 
  figs. 
  35 
  and 
  35 
  a, 
  which 
  represent 
  external 
  and 
  

   admedian 
  views 
  of 
  the 
  right 
  antenna. 
  The 
  most 
  noticeable 
  feature 
  is 
  the 
  

   great 
  development 
  of 
  the 
  external 
  lobe. 
  Small 
  and 
  inconspicuous 
  in 
  Notopus, 
  

   this 
  lobe 
  in 
  Ranina 
  forms 
  a 
  large 
  sinuous 
  ridge 
  which 
  projects 
  forward 
  as 
  far 
  

   as 
  the 
  anterior 
  limit 
  of 
  the 
  fourth 
  segment; 
  its 
  outer 
  margin 
  is 
  fringed 
  with 
  

   long 
  plumose 
  setae. 
  When 
  the 
  third 
  peduncular 
  segment 
  is 
  flexed 
  towards 
  

   the 
  middle 
  line, 
  the 
  lobe 
  in 
  question 
  is 
  brought 
  into 
  a 
  position 
  athwart 
  the 
  

   incomplete 
  lower 
  boundary 
  of 
  the 
  orbital 
  cavity, 
  and 
  forms 
  its 
  ventral 
  and 
  

   internal 
  wall, 
  the 
  long 
  fringe 
  of 
  hairs 
  on 
  what 
  is 
  now 
  its 
  anterior 
  margin 
  

   extending 
  upwards 
  across 
  the 
  orbital 
  cavity 
  and 
  interlocking 
  with 
  a 
  similar 
  

   fringe 
  spreading 
  downwards 
  from 
  the 
  supra-orbital 
  ridge 
  of 
  the 
  front 
  of 
  the 
  

   carapace. 
  For 
  brevity's 
  sake 
  this 
  lobe 
  will 
  be 
  referred 
  to 
  as 
  the 
  crest 
  of 
  the 
  

   third 
  peduncular 
  segment. 
  The 
  fourth 
  segment 
  is 
  sub-triangular 
  in 
  section 
  : 
  

   its 
  external 
  and 
  ventral 
  surfaces 
  are 
  convex 
  and 
  granular, 
  but 
  its 
  internal 
  

   surface 
  is 
  smooth, 
  slightly 
  concave, 
  and 
  flabelliform 
  in 
  outline. 
  Its 
  margins 
  

   are 
  surrounded 
  with 
  long 
  plumose 
  setae 
  the 
  disposition 
  of 
  which 
  is 
  shown 
  in 
  

   fig. 
  35a. 
  The 
  fifth 
  peduncular 
  segment 
  is 
  small 
  and 
  the 
  flagellum 
  rudi- 
  

   mentary 
  or 
  absent. 
  When 
  the 
  antennae 
  are 
  flexed 
  inwards, 
  the 
  concave 
  

   flabelliform 
  surfaces 
  of 
  the 
  fourth 
  segments 
  are 
  brought 
  nearly 
  into 
  contact 
  

   in 
  the 
  middle 
  line, 
  their 
  marginal 
  seta 
  3 
  interlock, 
  and 
  thus 
  a 
  narrow 
  but 
  deep 
  

   space 
  is 
  enclosed 
  which 
  is 
  continued 
  posteriorly 
  into 
  the 
  wider 
  space 
  bounded 
  

  

  