﻿240 
  Prof. 
  Carl 
  Chun 
  on 
  the 
  

  

  Suborder 
  I. 
  Haplophys^, 
  Chun. 
  

  

  Physoplioridae 
  with 
  an 
  unchambered 
  pneumatophore 
  which 
  

   is 
  partly 
  lined 
  by 
  secondary 
  ectoderm 
  functioning 
  as 
  a 
  gas- 
  

   gland 
  and 
  which 
  is 
  destitute 
  of 
  tracheae. 
  

  

  Tribe 
  I. 
  PHYSONECT^J, 
  Hack. 
  

   Family 
  Agalmidae, 
  Brandt. 
  

  

  23. 
  Halistemma 
  pictum, 
  Metschn. 
  

  

  The 
  elegant 
  Agalmid 
  described 
  by 
  Metschnikoff 
  as 
  Stepha- 
  

   nomia 
  picta, 
  and 
  afterwards 
  by 
  Claus 
  as 
  HaKstemma 
  tergesti- 
  

   num, 
  is 
  evidently 
  more 
  widely 
  distributed 
  than 
  has 
  hitherto 
  

   been 
  supposed. 
  It 
  occurred 
  very 
  frequently 
  from 
  January 
  to 
  

   April, 
  sometimes 
  in 
  enormously 
  long 
  specimens, 
  which 
  dis- 
  

   played 
  as 
  many 
  as 
  thirty-four 
  nectocalyces. 
  As 
  the 
  Mediter- 
  

   ranean 
  form 
  was 
  well 
  known 
  to 
  me 
  from 
  previous 
  investiga- 
  

   tions, 
  1 
  soon 
  convinced 
  myself 
  that 
  the 
  Canarian 
  species 
  is 
  

   perfectly 
  identical 
  with 
  it. 
  Although 
  Halistemma 
  pictum 
  

   has 
  been 
  accurately 
  described 
  by 
  Metschnikoff 
  and 
  Fuykas 
  

   and 
  monographically 
  treated 
  by 
  Claus, 
  certain 
  circumstances 
  

   which 
  have 
  escaped 
  the 
  above-mentioned 
  naturalists 
  seem 
  to 
  

   me 
  to 
  be 
  not 
  unimportant 
  in 
  connexion 
  with 
  the 
  conditions 
  of 
  

   growth 
  of 
  the 
  Physophorid 
  stem. 
  

  

  Law 
  of 
  Growth 
  of 
  the 
  Stem 
  of 
  Halistemma. 
  — 
  As 
  is 
  well 
  

   known, 
  there 
  is 
  at 
  the 
  base 
  of 
  the 
  column 
  of 
  nectocalyces 
  a 
  

   zone 
  of 
  gemmation 
  from 
  which 
  the 
  youngest 
  incipient 
  groups 
  

   of 
  the 
  Siphonophore-stem 
  originate. 
  The 
  groups 
  on 
  the 
  stem 
  

   therefore 
  increase 
  in 
  size 
  in 
  a 
  distal 
  direction 
  ; 
  the 
  groups 
  

   situated 
  at 
  the 
  end 
  of 
  the 
  stem 
  are 
  at 
  the 
  same 
  time 
  also 
  the 
  

   oldest. 
  Jn 
  those 
  Agalmidae 
  and 
  Forskalidae 
  which 
  are 
  cha- 
  

   racterized 
  by 
  separated 
  group-appendages 
  (" 
  dissolute 
  Cormi- 
  

   dien 
  " 
  of 
  Hlickel) 
  the 
  rule 
  above 
  cited, 
  that 
  the 
  appendages 
  of 
  

   the 
  stem 
  regularly 
  increase 
  in 
  age 
  (usually 
  also 
  in 
  size) 
  in 
  a 
  

   distal 
  direction, 
  applies 
  only 
  to 
  the 
  gastric 
  polyps 
  with 
  the 
  ten- 
  

   tacles 
  belonging 
  to 
  them. 
  Developmental 
  history 
  shows, 
  par- 
  

   ticularly 
  as 
  regards 
  Halistemma 
  pictum, 
  that, 
  in 
  point 
  of 
  fact, 
  

   the 
  gastric 
  polyps 
  seated 
  at 
  the 
  end 
  of 
  the 
  stem 
  are 
  the 
  oldest, 
  

   and 
  that 
  they 
  gradually 
  diminish 
  in 
  age 
  in 
  a 
  proximal 
  direc- 
  

   tion 
  — 
  that 
  is, 
  towards 
  the 
  nectostyle. 
  It 
  would, 
  however, 
  be 
  

   a 
  mistake 
  to 
  assume 
  that 
  the 
  same 
  condition 
  prevails 
  with 
  

   respect 
  to 
  the 
  other 
  appendages 
  of 
  the 
  stem, 
  namely 
  the 
  bracts, 
  

   palps, 
  palpal 
  filaments, 
  and 
  genital 
  bunches. 
  As 
  most 
  previous 
  

   observers 
  have 
  already 
  perceived, 
  the 
  latter 
  are 
  met 
  with 
  in 
  

  

  