﻿xo. 
  1946. 
  PACIFIC 
  MEDUSAE 
  AXD 
  S'IPIIONOPHORAE—BIGELOW. 
  37 
  

  

  Aequorid 
  which 
  has 
  them 
  is 
  Zygocanna 
  (of 
  which 
  I 
  have 
  studied 
  

   specimens 
  from 
  the 
  Phihppines), 
  with 
  branched 
  canals. 
  All 
  

   Aeqiiorids 
  with 
  unbranched 
  cansils 
  are 
  referred 
  here 
  to 
  Aequorea. 
  

   One 
  of 
  them, 
  groenlandica, 
  has 
  subumbral 
  papillae; 
  and 
  only 
  one, 
  

   j^ensile, 
  lacks 
  excretory 
  papillae. 
  

  

  Somewhat 
  to 
  my 
  surprise 
  a 
  character 
  which 
  proves 
  to 
  be 
  one 
  of 
  

   the 
  least 
  variable 
  in 
  Aequorea 
  is 
  a 
  trivial 
  one 
  — 
  that 
  is, 
  proportional 
  

   diameters 
  of 
  stomach 
  and 
  bell, 
  a 
  very 
  small 
  stomach, 
  only 
  about 
  one- 
  

   fourth 
  or 
  one-fifth 
  as 
  wide 
  as 
  the 
  bell, 
  distinguishing 
  A. 
  tenuis 
  and 
  its 
  

   close 
  ally, 
  A.jloridana, 
  from 
  all 
  other 
  Aequoreas. 
  

  

  The 
  forms 
  remaining 
  after 
  the 
  elimination 
  of 
  tenuis 
  ( 
  + 
  jioridana), 
  

   groenlandica, 
  and 
  'pensile, 
  are 
  all 
  closely 
  allied 
  to 
  one 
  another. 
  Van- 
  

   lioffen 
  (1911) 
  considers 
  the 
  relative 
  number 
  of 
  tentacles 
  and 
  canals 
  

   sufficiently 
  important 
  to 
  subdivide 
  them, 
  but 
  the 
  collection 
  which 
  I 
  

   have 
  studied 
  shows 
  that 
  it 
  can 
  not 
  be 
  used 
  as 
  a 
  specific 
  character, 
  

   because 
  there 
  is 
  an 
  unbroken 
  series 
  from 
  specimens 
  with 
  many 
  more 
  

   canals 
  than 
  tentacles, 
  to 
  ones 
  with 
  many 
  more 
  tentacles 
  than 
  canals. 
  

   The 
  only 
  tangible 
  character 
  for 
  this 
  purpose 
  seems 
  to 
  be 
  the 
  shape 
  of 
  

   the 
  tentacular 
  bulbs, 
  according 
  as 
  they 
  do 
  ("macrodactylum") 
  or 
  do 
  

   not 
  clasp 
  the 
  exumbrella 
  ("aequorea"). 
  But 
  the 
  Philippine 
  series 
  of 
  

   macrodactijlum 
  shows 
  that 
  the 
  clasps 
  vary 
  from 
  being 
  as 
  pronounced 
  

   as 
  figured 
  b}^ 
  Maas 
  (1905) 
  to 
  a 
  condition 
  where 
  it 
  is 
  difHcult 
  to 
  say 
  

   whether 
  they 
  are 
  present 
  or 
  not. 
  On 
  the 
  other 
  hand, 
  some 
  of 
  the 
  

   tentacles 
  in 
  one 
  of 
  the 
  specimens 
  from 
  Naples 
  which 
  I 
  have 
  studied 
  

   clasp 
  the 
  exumbrella 
  nearly 
  as 
  much 
  as 
  the 
  less 
  pronounced 
  ones 
  in 
  

   macrodactylum, 
  while 
  others 
  do 
  not, 
  but 
  are 
  constricted 
  at 
  the 
  base. 
  

   Thus 
  no 
  hard 
  and 
  fast 
  line 
  can 
  be 
  drawn 
  separating 
  the 
  extremes. 
  

   Nevertheless 
  it 
  is 
  usually, 
  if 
  not 
  always, 
  possible 
  to 
  place 
  a 
  given 
  

   specimen 
  in 
  one 
  group 
  or 
  the 
  other, 
  at 
  least 
  I 
  have 
  never 
  seen 
  one 
  

   absolutely 
  intermediate, 
  although 
  a 
  considerable 
  number 
  have 
  been 
  

   examined. 
  Here, 
  as 
  in 
  other 
  instances 
  among 
  medusae, 
  the 
  relation- 
  

   ship 
  of 
  the 
  two 
  can 
  be 
  best 
  represented 
  graphically 
  by 
  a 
  dumb-bell 
  

   shaped 
  figure, 
  not 
  by 
  two 
  isolated 
  circles. 
  And 
  although 
  we 
  do 
  not 
  

   know 
  whether 
  the 
  groups, 
  or 
  species, 
  have 
  been 
  differentiated 
  phylo- 
  

   genetically, 
  or 
  by 
  physiological 
  or 
  by 
  environmental 
  factors, 
  we 
  can 
  

   say, 
  from 
  the 
  kno^vn 
  records, 
  that 
  members 
  of 
  any 
  given 
  swarm 
  are 
  

   usuaUy 
  all 
  of 
  one 
  type 
  or 
  of 
  the 
  other, 
  while 
  all 
  recent 
  records 
  of 
  

   macrodactylum 
  are 
  from 
  the 
  Tropics 
  (Pacific, 
  and 
  one 
  Gulf 
  Stream) 
  ; 
  

   none 
  from 
  the 
  Mediterranean 
  or 
  colder 
  waters. 
  With 
  our 
  present 
  

   limited 
  knowledge 
  of 
  the 
  two 
  it 
  is 
  best 
  to 
  retain 
  macrodactylum 
  

   provisional!}^ 
  as 
  a 
  distinct 
  species. 
  

  

  All 
  remaining 
  Aequoreas 
  probably 
  belong 
  to 
  a 
  single 
  species, 
  

   A. 
  aequorea. 
  Most 
  of 
  the 
  Pacific 
  Aequoreas, 
  like 
  most 
  of 
  those 
  from 
  

   the 
  Adriatic 
  recorded 
  by 
  Glaus, 
  and 
  the 
  Naples 
  specimens 
  which 
  I 
  

   have 
  examined, 
  and 
  those 
  from 
  the 
  Tortugas 
  studied 
  by 
  Mayer 
  

  

  