﻿NO. 
  194(5. 
  PACIFIC 
  MEDUSAE 
  AND 
  SIPIIONOPHORAE—BIGELOW. 
  31 
  

  

  being 
  of 
  specimens 
  about 
  30 
  mm. 
  in 
  diameter, 
  with 
  a 
  hundred 
  tenta- 
  

   cles, 
  the 
  latter 
  of 
  ones 
  50-90 
  mm. 
  broad, 
  ^vith 
  about 
  340 
  tentacles. 
  

   The 
  present 
  series 
  is 
  intermediate 
  between 
  the 
  two: 
  35-50 
  mm. 
  

   in 
  diameter, 
  with 
  69-81 
  tentacles 
  to 
  the 
  quadrant, 
  a 
  total 
  of 
  from 
  

   200-250. 
  

  

  The 
  earlier 
  accounts 
  are 
  so 
  detailed 
  and 
  the 
  figures 
  so 
  satisfactory 
  

   that 
  there 
  is 
  little 
  to 
  be 
  added, 
  except 
  an 
  account 
  of 
  the 
  otocysts. 
  I 
  

   may 
  note, 
  however, 
  that 
  a 
  very 
  short 
  manubrium, 
  with 
  long, 
  crenulated 
  

   lips, 
  gonads 
  extending 
  over 
  most 
  of 
  the 
  length 
  of 
  the 
  radial 
  canals, 
  

   swollen 
  cylindrical 
  tentacular 
  bulbs, 
  and 
  entire 
  absence 
  of 
  cirri, 
  prove 
  

   to 
  be 
  constant 
  characters. 
  The 
  present 
  specimens 
  are 
  flatter 
  than 
  

   those 
  previously 
  recorded, 
  but 
  the 
  difference 
  may 
  be 
  due 
  to 
  preserva- 
  

   tion. 
  

  

  Sense 
  pits. 
  — 
  The 
  sense 
  pits 
  are 
  not 
  associated 
  with 
  ocelli, 
  thus 
  

   resembling 
  those 
  of 
  Cosmetira 
  and 
  Mitrocoma, 
  and 
  differing 
  from 
  the 
  

   corresponding 
  organs 
  in 
  Tiaropsis. 
  For 
  this 
  reason, 
  and 
  because, 
  

   at 
  least 
  in 
  formalin 
  material, 
  they 
  lack 
  otocysts 
  which 
  might 
  attract 
  

   attention 
  by 
  their 
  high 
  refrangibility, 
  they 
  are 
  very 
  easily 
  overlooked. 
  

   Indeed, 
  it 
  was 
  not 
  until 
  I 
  exaniined 
  a 
  specimen 
  under 
  the 
  compound 
  

   microscope 
  that 
  I 
  suspected 
  their 
  presence, 
  although 
  they 
  are 
  so 
  

   large 
  that 
  once 
  located 
  their 
  "open" 
  nature 
  is 
  easily 
  made 
  out 
  with 
  

   a 
  hand 
  lens. 
  Their 
  inconspicuous 
  nature 
  is 
  of 
  course 
  the 
  reason 
  that 
  

   they 
  were 
  not 
  observed 
  by 
  earlier 
  students. 
  As 
  in 
  Mitrocoma, 
  they 
  

   are 
  simple 
  pits 
  or 
  pockets 
  in 
  the 
  velum, 
  the 
  opening 
  being 
  on 
  the 
  

   subumbrella 
  side, 
  lying 
  close 
  to 
  the 
  marginal 
  ring. 
  Their 
  number 
  is 
  

   variable; 
  in 
  one 
  quadrant 
  (with 
  79 
  tentacles) 
  there 
  were 
  six, 
  in 
  

   another 
  (81 
  tentacles) 
  only 
  three; 
  in 
  a 
  third, 
  six 
  in 
  the 
  two-thirds 
  

   which 
  is 
  intact, 
  and 
  in 
  one 
  quadrant, 
  which 
  was 
  well 
  preserved, 
  I 
  

   could 
  find 
  none. 
  I 
  could 
  not 
  count 
  them 
  over 
  the 
  whole 
  margin 
  of 
  

   any 
  specimen. 
  Judging 
  from 
  these 
  quadrants, 
  we 
  may 
  assume, 
  

   tentatively, 
  a 
  total 
  of 
  12-24. 
  Structurally 
  the 
  pits 
  closely 
  resemble 
  

   these 
  of 
  Mitrocoma 
  (O. 
  and 
  R. 
  Hertwig, 
  1878, 
  pi. 
  7, 
  fig. 
  14), 
  except 
  

   that 
  no 
  otoliths 
  could 
  be 
  found. 
  As 
  is 
  seen 
  in 
  cross 
  section 
  the 
  

   pits 
  are 
  flatter 
  than 
  a 
  hemisphere, 
  and 
  the 
  exumbrellar 
  ectoderm 
  

   covering 
  them 
  consists 
  of 
  high, 
  columnar 
  cells, 
  which 
  merge 
  into 
  the 
  

   much 
  smaller 
  ceils 
  of 
  the 
  exumbral 
  surface 
  of 
  the 
  velum 
  at 
  the 
  outer 
  

   margin, 
  while 
  centrally 
  the}^ 
  merge 
  into 
  the 
  marginal 
  ring. 
  A 
  very 
  

   thin 
  "stuzlamella" 
  separates 
  these 
  large 
  cells 
  from 
  the 
  much 
  smaller 
  

   ones 
  composing 
  the 
  subumbrellar 
  layer, 
  clearly 
  visible 
  in 
  optical 
  sec- 
  

   tions. 
  It 
  is 
  in 
  this 
  layer, 
  of 
  course, 
  that 
  the 
  otoliths 
  are 
  to 
  be 
  sought, 
  

   but 
  no 
  such 
  structures 
  can 
  be 
  found. 
  The 
  only 
  thing 
  suggesting 
  that 
  

   they 
  were 
  present 
  in 
  life, 
  but 
  have 
  been 
  destroyed 
  by 
  the 
  formalin 
  in 
  

   which 
  the 
  specimens 
  are 
  preserved 
  is 
  that 
  the 
  cells 
  of 
  the 
  subum- 
  

   brellar 
  layer, 
  within 
  the 
  pit, 
  are 
  occasionally 
  replaced 
  by 
  large, 
  

   irregular 
  masses 
  which 
  may 
  be 
  the 
  remnants 
  of 
  the 
  otolith 
  cells. 
  

  

  