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  PROFESSORS 
  EDWARD 
  FORBES 
  AND 
  J. 
  GOODSIR 
  ON 
  SOME 
  

  

  nearly 
  on 
  the 
  same 
  level. 
  The 
  outer 
  tunic 
  is 
  a 
  smooth 
  and 
  transparent 
  softly 
  

   cartilaginous 
  sac 
  of 
  a 
  pale 
  emerald 
  green 
  tint, 
  slightly 
  swelling 
  out 
  above 
  the 
  

   centre, 
  and 
  contracted, 
  but 
  not 
  pedunculated 
  at 
  the 
  base. 
  The 
  inner 
  tunic 
  is 
  

   clearly 
  seen 
  through 
  the 
  walls 
  of 
  the 
  outer 
  ; 
  it 
  is 
  rather 
  less 
  in 
  dimensions 
  than 
  

   the 
  outer, 
  and 
  its 
  shape 
  is 
  plainly 
  indicated 
  by 
  the 
  opaque 
  white 
  lines 
  which 
  

   mark 
  its 
  boundaries. 
  The 
  orifices 
  of 
  the 
  outer 
  tunic 
  are 
  both 
  quite 
  plain 
  ; 
  the 
  

   branchial 
  one 
  is 
  rather 
  longer 
  than 
  the 
  anal, 
  as 
  is 
  also 
  the 
  case 
  with 
  the 
  openings 
  

   of 
  the 
  inner 
  tunic. 
  The 
  branchial 
  orifice 
  of 
  the 
  latter 
  is 
  fringed 
  with 
  a 
  circle 
  of 
  

   pointed 
  tentacula 
  more 
  than 
  twelve 
  in 
  number 
  ; 
  its 
  anal 
  orifice 
  is 
  at 
  the 
  end 
  of 
  a 
  

   short 
  tube, 
  and 
  has 
  no 
  tentacula, 
  but 
  six 
  conspicuous 
  white 
  ocelli. 
  Beneath 
  the 
  

   branchial 
  orifice 
  are 
  two 
  crescentic 
  white 
  lines, 
  at 
  the 
  summit 
  of 
  a 
  single 
  white 
  

   line 
  which 
  runs 
  down 
  the 
  branchial 
  side 
  of 
  the 
  body; 
  under 
  the 
  anal 
  orifice 
  

   there 
  is 
  a 
  short 
  oblique 
  central 
  white 
  line 
  running 
  from 
  the 
  neighbourhood 
  of 
  a 
  

   large 
  ganglion 
  to 
  the 
  summit 
  of 
  two 
  white 
  lines 
  uniting 
  in 
  a 
  loop 
  at 
  the 
  point 
  

   of 
  junction, 
  and 
  running 
  down 
  the 
  visceral 
  side 
  of 
  the 
  body. 
  The 
  chief 
  visceral 
  

   mass 
  is 
  seen 
  at 
  the 
  base 
  of 
  this 
  line 
  imbedded 
  in 
  the 
  common 
  pedicle. 
  

  

  When 
  the 
  entire 
  mass 
  was 
  first 
  dredged 
  up, 
  many 
  of 
  the 
  tests 
  appeared 
  as 
  if 
  

   emptied 
  of 
  their 
  contents., 
  or 
  as 
  if 
  the 
  inner 
  tunic 
  and 
  viscera 
  had 
  not 
  become 
  

   developed. 
  After 
  it 
  had 
  for 
  some 
  time 
  remained 
  at 
  rest 
  in 
  a 
  vessel 
  of 
  sea-water, 
  

   to 
  our 
  great 
  surprise 
  we 
  found 
  all 
  the 
  sacs 
  filled 
  up 
  again. 
  On 
  closer 
  examina- 
  

   tion, 
  we 
  found 
  that 
  the 
  inner 
  tunic 
  is 
  exceedingly 
  irritable, 
  and 
  can 
  withdraw 
  

   itself 
  like 
  the 
  finger 
  of 
  a 
  glove, 
  entirely 
  independent 
  of 
  the 
  outer 
  tunic, 
  and 
  hide 
  

   itself 
  in 
  the 
  common 
  mass 
  or 
  peduncles. 
  This 
  is 
  done 
  very 
  rapidly 
  sometimes, 
  

   at 
  other 
  times 
  rather 
  slowly; 
  most 
  rapidly 
  when 
  the 
  ganglionic 
  mass 
  between 
  the 
  

   orifices 
  is 
  pinched 
  or 
  otherwise 
  irritated. 
  When 
  we 
  squeezed 
  it 
  with 
  the 
  forceps, 
  

   the 
  withdrawal 
  of 
  the 
  common 
  branchial 
  sacs 
  was 
  almost 
  instantaneous. 
  

  

  The 
  genus 
  Syntethys 
  differs 
  from 
  Diazona 
  in 
  the 
  structure 
  of 
  the 
  branchial 
  

   and 
  anal 
  orifices, 
  which, 
  instead 
  of 
  being 
  six-rayed, 
  as 
  in 
  the 
  latter 
  genus, 
  are 
  

   simple 
  and 
  even-edged 
  as 
  in 
  Clavelina 
  ; 
  moreover, 
  instead 
  of 
  having 
  a 
  peduncu- 
  

   lated, 
  it 
  has 
  a 
  sessile 
  abdomen. 
  The 
  structure 
  and 
  form 
  of 
  the 
  common 
  mass 
  is 
  

   similar, 
  making 
  a 
  strong 
  distinction 
  between 
  it 
  and 
  Clavelina. 
  The 
  following- 
  

   summary 
  of 
  the 
  characters 
  of 
  Syntethys 
  will 
  serve 
  to 
  compare 
  them 
  with 
  those 
  of 
  

   the 
  genera 
  described 
  by 
  Savigny. 
  

  

  Common 
  mass 
  sessile, 
  gelatinous, 
  forming 
  a 
  single 
  orbicular 
  system. 
  Indivi- 
  

   duals 
  very 
  prominent, 
  arranged 
  subconcentrically. 
  Branchial 
  and 
  anal 
  orifices 
  

   simple, 
  and 
  not 
  cut 
  into 
  rays. 
  

  

  Thorax 
  oblong 
  and 
  cylindrical. 
  Branchial 
  chamber 
  with 
  thirteen 
  transverse 
  

   rows 
  of 
  oblong 
  openings, 
  fringed 
  with 
  ciliated 
  epithelium 
  ; 
  hooked 
  fleshy 
  tubercles 
  

   at 
  the 
  intersections 
  of 
  the 
  branchial 
  meshes, 
  each 
  mesh 
  presenting 
  one 
  of 
  the 
  

   ciliated 
  openings 
  ; 
  the 
  tubercles 
  give 
  the 
  internal 
  surface 
  of 
  the 
  chamber 
  a 
  dotted 
  

   appearance. 
  

  

  