﻿Siphonophora 
  of 
  the 
  Canary 
  Islands. 
  221 
  

  

  Medusas 
  and 
  also 
  specially 
  the 
  primary 
  nectocalyx 
  in 
  the 
  

   Calycophoridae. 
  I 
  am 
  therefore 
  the 
  more 
  surprised 
  that 
  

   Hiickel 
  declares 
  categorically: 
  — 
  "This 
  latter 
  conception 
  is, 
  

   in 
  my 
  opinion, 
  quite 
  erroneous 
  ; 
  the 
  former, 
  in 
  a 
  certain 
  sense, 
  

   admissible. 
  The 
  comparative 
  ontogeny 
  of 
  the 
  Siphonophora 
  

   appears 
  to 
  me 
  to 
  prove 
  definitely 
  that 
  the 
  air-sac 
  is 
  an 
  apical 
  

   gas-gland 
  of 
  the 
  exoderm, 
  which 
  in 
  the 
  Disconula 
  of 
  the 
  

   Disconanthae 
  immerses 
  itself 
  into 
  the 
  jelly 
  of 
  the 
  umbrella 
  

   centrally 
  at 
  the 
  vertex 
  of 
  the 
  umbrella, 
  but 
  in 
  the 
  Siphonula 
  

   of 
  the 
  Siphonanthae 
  excentrically 
  near 
  the 
  vertex." 
  

  

  In 
  the 
  first 
  place 
  as 
  regards 
  the 
  last 
  observation, 
  in 
  which 
  

   the 
  endeavour 
  to 
  establish 
  a 
  fundamental 
  distinction 
  between 
  

   the 
  Disconula 
  and 
  the 
  Siphonula 
  is 
  revealed, 
  it 
  is 
  not 
  at 
  all 
  

   correct. 
  In 
  simple 
  Physophoridae, 
  as, 
  for 
  example, 
  in 
  the 
  

   larva 
  of 
  Halistemma 
  pictum, 
  the 
  pneumatophore 
  originates 
  

   exactly 
  at 
  the 
  apical 
  (aboral) 
  pole 
  of 
  the 
  ciliated 
  larva, 
  as 
  

   Metschnikoff 
  has 
  already 
  correctly 
  shown, 
  and 
  as 
  I 
  was 
  able 
  

   to 
  ascertain 
  in 
  the 
  Canarian 
  species. 
  

  

  While, 
  on 
  the 
  other 
  hand, 
  Metschnikoff 
  leaves 
  us 
  in 
  no 
  

   doubt 
  as 
  to 
  where, 
  according 
  to 
  his 
  view, 
  we 
  have 
  to 
  seek 
  

   the 
  subumbrella 
  of 
  the 
  Medusa 
  modified 
  into 
  a 
  pneumato- 
  

   phore, 
  we 
  find 
  in 
  Hiickel 
  no 
  indication 
  of 
  a 
  part 
  of 
  the 
  pneu- 
  

   matophore 
  homologous 
  with 
  the 
  subumbrella. 
  Nor 
  does 
  he 
  

   adduce 
  from 
  the 
  comparative 
  ontogeny 
  of 
  the 
  Siphonophora 
  

   any 
  fact 
  which 
  can 
  justify 
  his 
  view. 
  I 
  have 
  myself' 
  pre- 
  

   viously 
  appealed 
  emphatically 
  to 
  developmental 
  history, 
  and 
  

   can 
  now 
  once 
  more 
  assert 
  that 
  the 
  ciliated 
  larva 
  of 
  Hali- 
  

   stemma 
  is 
  similar 
  in 
  form 
  to 
  the 
  larvae 
  of 
  Calycophoridae 
  of 
  

   the 
  same 
  age. 
  Why, 
  then, 
  in 
  the 
  one 
  case 
  we 
  should 
  admit 
  

   that 
  the 
  ectodermal 
  introverted 
  bud-nucleus 
  becomes 
  deve- 
  

   loped 
  into 
  the 
  subumbrella 
  of 
  the 
  primary 
  nectocalyx, 
  while 
  

   in 
  the 
  other 
  a 
  part 
  of 
  the 
  exumbrella 
  proceeds 
  from 
  the 
  bud- 
  

   nucleus, 
  which 
  is 
  introverted 
  in 
  exactly 
  the 
  same 
  manner, 
  is 
  

   incomprehensible 
  to 
  me, 
  and 
  contradicts 
  all 
  observations 
  upon 
  

   the 
  comparative 
  ontogeny 
  of 
  the 
  Siphonophora. 
  

  

  I 
  must 
  admit 
  that 
  Hackel's 
  u 
  Medusa 
  Theory," 
  both 
  in 
  its 
  

   general 
  foundation 
  and 
  in 
  its 
  special 
  working 
  out, 
  seems 
  to 
  ma 
  

   not 
  to 
  be 
  a 
  fortunate 
  attempt 
  to 
  combine 
  the 
  opposite 
  views 
  of 
  

   Huxley, 
  Metschnikoff, 
  and 
  P. 
  E. 
  Miiller 
  with 
  those 
  of 
  

   Leuckart 
  and 
  Vogt, 
  with 
  the 
  latter 
  of 
  which 
  Hiickel 
  also 
  

   formerly 
  agreed. 
  

  

  Passing 
  now 
  to 
  my 
  statements 
  with 
  regard 
  to 
  the 
  Cana- 
  

   rian 
  Siphonophora, 
  which, 
  indeed, 
  must 
  have 
  a 
  modest 
  

   Ann. 
  & 
  Mag. 
  N. 
  Hist. 
  Ser. 
  6, 
  Vol. 
  iii. 
  16 
  

  

  