﻿216 
  Prof. 
  Carl 
  Chun 
  on 
  the 
  

  

  that 
  Hack 
  el 
  founds 
  his 
  speculations 
  upon 
  two 
  larval 
  forms 
  of 
  

   very 
  different 
  morphological 
  value. 
  The 
  radiate 
  Disconula 
  

   represents 
  a 
  much 
  altered 
  larva, 
  which 
  was 
  certainly 
  preceded 
  

   by 
  a 
  bilateral 
  Siphonula-stage. 
  Unfortunately 
  we 
  are 
  still 
  

   unacquainted 
  with 
  the 
  embryonic 
  development 
  of 
  the 
  Velelhe 
  

   and 
  Porpitce 
  ; 
  but 
  I 
  have 
  every 
  reason 
  to 
  think 
  that 
  the 
  

   younger 
  stages 
  closely 
  approach 
  the 
  youngest 
  larval 
  stages 
  

   of 
  Physalia 
  in 
  structure. 
  Young 
  Eatarice 
  observed 
  by 
  me 
  

   which 
  still 
  possess 
  a 
  simple 
  unchambered 
  pneumatophore 
  

   show 
  four 
  tentacles, 
  which 
  are 
  bilaterally 
  arranged 
  on 
  one 
  

   side, 
  or, 
  more 
  accurately, 
  present 
  with 
  one 
  large 
  tentacle 
  

   three 
  smaller 
  ones 
  asymmetrically 
  distributed. 
  This 
  stage 
  was 
  

   certainly 
  preceded 
  by 
  a 
  true 
  bilateral 
  Siphonula 
  with 
  the 
  

   rudiment 
  of 
  the 
  pneumatophore, 
  a 
  single 
  tentacle, 
  and 
  the 
  

   stomachal 
  sac. 
  This 
  stage, 
  which 
  certainly 
  has 
  not 
  yet 
  been 
  

   observed, 
  must 
  be 
  paralleled 
  with 
  the 
  Siphonula 
  ; 
  but 
  then 
  

   one 
  would 
  hesitate 
  a 
  priori 
  to 
  recognize 
  a 
  fundamental 
  dis- 
  

   tinction 
  between 
  " 
  Siphonanthre 
  " 
  and 
  " 
  Disconanthae," 
  and 
  

   to 
  give 
  expression 
  to 
  this 
  condition 
  by 
  seeking 
  a 
  relationship 
  

   for 
  the 
  DisconantliEe 
  with 
  the 
  Traehomedusae 
  and 
  for 
  the 
  

   Siphonanthae 
  with 
  the 
  Anthomedusse. 
  

  

  In 
  accordance 
  with 
  previous 
  naturalists 
  I 
  see 
  in 
  the 
  Velel- 
  

   lidae 
  true 
  Physophorida?, 
  which 
  certainly 
  in 
  their 
  adaptation 
  

   to 
  a 
  passive 
  movement 
  by 
  action 
  of 
  the 
  wind 
  show 
  very 
  

   plainly 
  the 
  transformations 
  already 
  stamped 
  upon 
  the 
  Dis- 
  

   conula. 
  1 
  have 
  repeatedly 
  referred 
  to 
  these 
  adaptations 
  and 
  

   need 
  only 
  indicate 
  here 
  that 
  I 
  regard 
  as 
  an 
  adaptation 
  to 
  the 
  

   floating 
  mode 
  of 
  life 
  in 
  the 
  deep 
  sea, 
  i. 
  e. 
  at 
  the 
  surface, 
  as 
  a 
  

   later 
  acquisition, 
  and 
  consequently 
  as 
  an 
  organ 
  sui 
  generis, 
  

   the 
  mantle 
  which 
  was 
  interpreted 
  by 
  Hackel, 
  in 
  agreement 
  

   with 
  Metschnikoff, 
  as 
  a 
  Medusan 
  umbrella. 
  This 
  limb 
  or 
  

   mantle, 
  circular 
  in 
  the 
  Porpitce, 
  oval 
  in 
  the 
  clinoradially 
  con- 
  

   structed 
  Velelhe, 
  commences 
  in 
  the 
  youngest 
  larvae 
  as 
  a 
  narrow 
  

   fold 
  around 
  the 
  still 
  unchambered 
  pneumatophore, 
  and 
  is 
  

   certainly 
  deficient 
  in 
  the 
  Siphonula-st&ge 
  of 
  the 
  Velellidae 
  as 
  

   postulated 
  by 
  me. 
  It 
  originates 
  therefore 
  in 
  the 
  same 
  way 
  

   as 
  the 
  principal 
  muscular 
  border 
  of 
  the 
  sail 
  in 
  a 
  Rataria. 
  If 
  

   we 
  were 
  to 
  homologize 
  this 
  mantle 
  with 
  an 
  umbrella 
  we 
  should 
  

   obtain 
  a 
  Medusa 
  which 
  presented 
  upon 
  its 
  exumbrella 
  a 
  richly 
  

   developed 
  vascular 
  reticulation 
  and 
  a 
  powerful 
  coat 
  of 
  epi- 
  

   thelial 
  muscular 
  cells 
  — 
  structural 
  characters 
  which 
  we 
  only 
  

   meet 
  with 
  in 
  the 
  subumbrella. 
  

  

  There 
  are 
  also 
  some 
  of 
  liackel's 
  special 
  interpretations 
  of 
  

   the 
  structure 
  of 
  the 
  Yeleliidaj 
  with 
  which 
  I 
  cannot 
  agree. 
  

   Thus 
  he 
  regards 
  the 
  ectodermal 
  parenchyma 
  placed 
  between 
  

   the 
  hepatic 
  tubes 
  as 
  a 
  gas-gland, 
  which 
  secretes 
  the 
  air 
  into 
  

  

  