﻿220 
  Prof. 
  Carl 
  Chun 
  on 
  the 
  

  

  illustrated 
  by 
  an 
  example. 
  As 
  is 
  well 
  known, 
  there 
  are 
  

   Eudoxias 
  which, 
  besides 
  the 
  genital 
  calyx, 
  possess 
  a 
  special 
  

   sterile 
  nectocalyx 
  destitute 
  of 
  manubrium. 
  The 
  latter, 
  

   according 
  to 
  Hackel, 
  represents 
  a 
  Medusan 
  persona, 
  when 
  he 
  

   assumes 
  that 
  in 
  it 
  the 
  manubrium 
  has 
  been 
  suppressed 
  by 
  

   retrogression. 
  But 
  why 
  are 
  we 
  to 
  regard 
  the 
  locomotive 
  

   elements 
  merely 
  as 
  organs, 
  seeing 
  that 
  they 
  possess 
  exactly 
  

   the 
  same 
  attributes 
  as 
  the 
  special 
  sterile 
  nectocalyx 
  ? 
  I 
  readily 
  

   admit 
  that 
  it 
  may 
  be 
  a 
  matter 
  of 
  dispute 
  whether 
  in 
  the 
  poly- 
  

   morphic 
  colony 
  we 
  are 
  to 
  regard 
  the 
  bracts 
  and 
  tentacles 
  as 
  indi- 
  

   viduals 
  or 
  as 
  organs, 
  although 
  Hackel 
  himself 
  cites 
  facts 
  (such 
  

   as 
  the 
  occurrence 
  of 
  a 
  small 
  umbrella 
  on 
  the 
  bracts 
  of 
  Aihorybia 
  

   and 
  Rhochphysa) 
  which 
  might 
  support 
  the 
  former 
  notion. 
  If 
  

   the 
  dispute 
  were 
  to 
  turn 
  only 
  upon 
  the 
  precarious 
  determina- 
  

   tion 
  of 
  the 
  boundary 
  between 
  individual 
  and 
  organ 
  I 
  would 
  

   not 
  proceed 
  further 
  in 
  this 
  place 
  ; 
  but 
  the 
  special 
  form 
  in 
  

   which 
  Hackel 
  clothes 
  his 
  statements 
  induces 
  me 
  to 
  test 
  more 
  

   closely 
  his 
  assertion 
  as 
  to 
  the 
  characteristic 
  attribute 
  of 
  the 
  

   Physophoridae, 
  namely 
  the 
  pneumatophore. 
  

  

  I 
  am 
  glad 
  in 
  the 
  first 
  place 
  that 
  Hackel 
  adopts 
  my 
  view 
  as 
  

   to 
  the 
  homology 
  of 
  the 
  primary 
  nectocalyx 
  of 
  the 
  Calyco- 
  

   phoridse 
  and 
  the 
  pneumatophore 
  of 
  the 
  Physophorida?. 
  t 
  

   believe 
  that 
  by 
  the 
  demonstration 
  in 
  the 
  Calycophoridse 
  of 
  a 
  

   primary 
  calyx 
  which 
  is 
  thrown 
  off 
  and 
  replaced 
  by 
  hetero- 
  

   morphous 
  secondary 
  calyces, 
  as 
  well 
  as 
  by 
  the 
  homologization 
  

   of 
  this 
  nectocalyx 
  with 
  a 
  Medusa 
  converted 
  by 
  change 
  of 
  

   function 
  into 
  a 
  pneumatophore, 
  a 
  step 
  in 
  advance 
  is 
  made 
  

   with 
  regard 
  to 
  the 
  explanation 
  of 
  the 
  production 
  of 
  that 
  

   hydrostatic 
  apparatus. 
  As 
  to 
  the 
  fact 
  that 
  the 
  pneumato- 
  

   phore 
  represents 
  a 
  metamorphosed 
  Medusa, 
  i. 
  e. 
  umbrella, 
  all 
  

   observers 
  are 
  in 
  accord 
  ; 
  it 
  is 
  only 
  in 
  the 
  special 
  proof 
  that 
  

   they 
  differ 
  essentially 
  from 
  one 
  another. 
  Metschnikoff, 
  as 
  is 
  

   well 
  known, 
  regards 
  the 
  pneumatophore 
  as 
  an 
  everted 
  

   Medusan 
  umbrella, 
  of 
  which 
  the 
  exumbrella 
  has 
  been 
  con- 
  

   verted 
  into 
  the 
  internal 
  cavity 
  filled 
  with 
  air. 
  If 
  this 
  con- 
  

   ception 
  should 
  be 
  verified, 
  an 
  essential 
  difficulty 
  in 
  the 
  way 
  of 
  

   the 
  comparison 
  of 
  a 
  Physophorid 
  to 
  a 
  budding 
  Sarsia, 
  namely 
  

   the 
  dislocation 
  of 
  the 
  gemmiparous 
  manubrium, 
  would 
  be 
  got 
  

   rid 
  of. 
  We 
  should 
  then 
  only 
  have 
  to 
  explain 
  how 
  in 
  this 
  case, 
  in 
  

   the 
  homologous 
  primary 
  nectocalyx 
  of 
  the 
  Calycophoridse, 
  the 
  

   stomachal 
  peduncle 
  with 
  its 
  buds 
  does 
  not 
  hang 
  out 
  from 
  the 
  

   subumbrella, 
  but 
  appears 
  dislocated 
  upon 
  the 
  exumbrella. 
  

   But 
  the 
  history 
  of 
  development 
  cannot 
  in 
  any 
  way 
  justify 
  

   such 
  a 
  view. 
  The 
  ectodermal 
  bud-nucleus, 
  by 
  means 
  of 
  

   which 
  the 
  pneumatophore 
  is 
  founded, 
  is 
  perfectly 
  homologous 
  

   with 
  the 
  bud- 
  nucleus 
  which 
  forms 
  the 
  subumbrella 
  of 
  all 
  

  

  