﻿364 
  MARGKRY 
  MOSELEY. 
  

  

  the 
  first 
  maxilliped 
  be 
  torn 
  from 
  the 
  animal 
  tlie 
  cushion 
  and 
  

   gill 
  stay 
  behind. 
  This 
  position 
  corresponds 
  to 
  that 
  assigned 
  

   by 
  Clans 
  ^ 
  to 
  the 
  rudimentary 
  gill 
  on 
  the 
  first 
  maxilliped 
  in 
  

   Peneeus, 
  as 
  he 
  objected 
  to 
  the 
  two 
  arthrobranchs 
  of 
  Huxley 
  

   being 
  classed 
  together, 
  and 
  considered 
  the 
  posterior 
  one 
  as 
  

   having 
  a 
  closer 
  relation 
  to 
  the 
  series 
  of 
  pleurobranchise. 
  The 
  

   epipodite 
  passes 
  posteriorly 
  to 
  the 
  gill 
  and 
  touching 
  it. 
  

  

  The 
  amount 
  of 
  development 
  of 
  this 
  gill, 
  as 
  with 
  most 
  

   rudimentary 
  organs, 
  is 
  very 
  variable, 
  but 
  it 
  was 
  fairly 
  equally 
  

   developed 
  on 
  the 
  two 
  sides 
  of 
  the 
  animals 
  I 
  have 
  examined 
  

   (figs. 
  5 
  and 
  7, 
  also 
  4 
  and 
  6, 
  from 
  same 
  specimens) 
  ; 
  also 
  

   it 
  varies 
  equally 
  in 
  development 
  in 
  males 
  and 
  females. 
  In 
  

   the 
  better 
  developed 
  specimens 
  in 
  which 
  there 
  is 
  a 
  central 
  

   stem 
  the 
  filaments 
  of 
  the 
  gill 
  are 
  all 
  developed 
  on 
  the 
  outer 
  

   side 
  of 
  this 
  stem 
  (figs. 
  1, 
  3, 
  4, 
  7). 
  The 
  filaments 
  are 
  fre- 
  

   quently 
  discoloured 
  with 
  brown 
  patches. 
  

  

  According 
  to 
  Dr. 
  Caiman 
  the 
  only 
  other 
  Decapods 
  known 
  

   to 
  possess 
  branchiae 
  on 
  the 
  first 
  thoracic 
  somite^ 
  are 
  

   Stenopus, 
  some 
  Pengeidfe, 
  and 
  certain 
  aberrant 
  Thalassi- 
  

   nidas 
  (J 
  axe 
  a 
  and 
  Naushonia) 
  which 
  possess 
  a 
  minute 
  

   arthrobranch 
  on 
  each 
  side 
  of 
  that 
  somite. 
  

  

  In 
  Pen 
  sens 
  the 
  gill 
  is 
  less 
  rudimentary 
  than 
  in 
  A. 
  f 
  luvia- 
  

   tilis, 
  and 
  rests 
  on 
  a 
  fleshy 
  lobe 
  or 
  cushion 
  in 
  the 
  same 
  position 
  

   as 
  that 
  in 
  Astacus, 
  but 
  which 
  stands 
  out 
  straight 
  from 
  the 
  

   body 
  of 
  the 
  animal 
  instead 
  of 
  lying 
  flat 
  against 
  it 
  as 
  in 
  A. 
  

   f 
  luviatilis. 
  The 
  filaments 
  of 
  the 
  gill, 
  of 
  which 
  there 
  are 
  many 
  

   more 
  than 
  in 
  A. 
  flu 
  via 
  til 
  is, 
  all 
  spring 
  from 
  the 
  cushion 
  in 
  a 
  

   fan 
  shape, 
  not 
  from 
  a 
  central 
  stem 
  as 
  in 
  A. 
  fluviatilis. 
  

  

  As 
  before 
  mentioned, 
  this 
  gill 
  is 
  only 
  found 
  in 
  A. 
  fluvia- 
  

   tilis, 
  Stenopus, 
  and 
  some 
  Penseidee 
  and 
  Thalassinidse; 
  

   however, 
  in 
  A. 
  dauricus 
  there 
  was 
  the 
  minute 
  papilla 
  on 
  

   the 
  right 
  side 
  of 
  the 
  specimen 
  I 
  examined, 
  and 
  there 
  seem 
  to 
  

   be 
  traces 
  of 
  the 
  gill 
  in 
  some 
  other 
  of 
  the 
  allied 
  forms 
  which 
  

   I 
  examined. 
  

  

  1 
  ' 
  Arb. 
  Zool. 
  Inst. 
  Wien/ 
  tome 
  G, 
  p. 
  46, 
  1886. 
  

  

  - 
  Apart 
  from 
  the 
  branchial 
  filaments 
  developed 
  on 
  the 
  epipodite 
  of 
  the 
  first 
  

   maxilliped 
  in 
  many 
  Parastacinse. 
  

  

  