﻿Structure 
  o/" 
  Magelona. 
  455 
  

  

  action 
  of 
  the 
  water 
  laterally, 
  and 
  presents 
  in 
  the 
  fresh 
  

   animal 
  the 
  aspect 
  of 
  a 
  granular 
  area 
  crossed 
  by 
  numerous 
  

   convolutions 
  or 
  folds, 
  which 
  often 
  change 
  their 
  appearance 
  

   under 
  examination, 
  like 
  those 
  formed 
  in 
  a 
  translucent 
  and 
  

   very 
  fine 
  chitinous 
  membrane. 
  The 
  whole, 
  iudeed, 
  simulates 
  

   a 
  convoluted 
  duct 
  most 
  closely, 
  since 
  the 
  folds 
  retain 
  a 
  

   uniform 
  size 
  throughout, 
  though 
  they 
  are 
  finer 
  at 
  one 
  end 
  of 
  

   the 
  mass. 
  The 
  latter 
  can 
  with 
  care 
  be 
  enucleated 
  from 
  its 
  

   covering, 
  but 
  in 
  those 
  examined 
  no 
  clear 
  evidence 
  of 
  well- 
  

   formed 
  ducts 
  {e.g. 
  indication 
  of 
  a 
  central 
  cavity 
  or 
  an 
  entirely 
  

   free 
  coil, 
  on 
  tearing) 
  could 
  be 
  observed. 
  It 
  is 
  possible 
  that 
  

   the 
  ambiguous 
  structure 
  was 
  only 
  partially 
  developed 
  and 
  

   that 
  the 
  folds 
  may 
  afterwards 
  attain 
  further 
  differentiation. 
  

   The 
  exact 
  function 
  of 
  this 
  structure 
  is 
  unknown, 
  and 
  its 
  

   presence 
  in 
  both 
  sexes 
  would 
  show 
  that 
  it 
  is 
  not 
  indispensably 
  

   related 
  to 
  the 
  ova. 
  It 
  appears 
  to 
  be 
  homologous 
  with 
  the 
  

   external 
  ovaries 
  or 
  egg-racemes 
  described 
  by 
  Prof. 
  Mbbius 
  in 
  

   Leipoceras 
  uviferum, 
  a 
  form 
  which 
  closely 
  resembles 
  Polydora*. 
  

   It 
  is 
  still 
  more 
  nearly 
  related 
  to 
  the 
  egg-sacs 
  (resembling 
  a 
  

   swallow's 
  nest) 
  mentioned 
  by 
  the 
  same 
  author 
  as 
  present 
  

   along 
  the 
  sides 
  of 
  Scolecolepis 
  cirrata, 
  Sars 
  f. 
  It 
  may 
  be 
  

   that 
  the 
  folded 
  structure 
  in 
  Magelona 
  acts 
  the 
  part 
  of 
  the 
  

   network 
  in 
  Scolecolepis, 
  by 
  which 
  the 
  eggs 
  are 
  held 
  in 
  the 
  

   pouches, 
  but 
  no 
  proof 
  of 
  this 
  has 
  yet 
  been 
  observed. 
  The 
  

   whole 
  arrangement, 
  however, 
  seems 
  to 
  be 
  much 
  more 
  largely 
  

   developed 
  in 
  Magelona. 
  The 
  analogy 
  of 
  this 
  structure 
  with 
  

   a 
  segmental 
  organ 
  can 
  only 
  be 
  conjectural, 
  though 
  it 
  is 
  

   suggestive 
  that 
  M. 
  Claparede 
  describes 
  a 
  similar 
  but 
  more 
  

   highly 
  differentiated 
  organ 
  within 
  the 
  posterior 
  region 
  of 
  the 
  

   body 
  in 
  Chcetopterus. 
  Finally, 
  so 
  little 
  is 
  known 
  of 
  the 
  life- 
  

   history 
  of 
  Magelona, 
  that 
  nothing 
  can 
  be 
  said 
  of 
  its 
  connection 
  

   with 
  sexual 
  or 
  other 
  variations. 
  

  

  No 
  opportunity, 
  unfortunately, 
  was 
  available 
  for 
  investi- 
  

   gating 
  the 
  development 
  of 
  the 
  species 
  at 
  St. 
  Andrews. 
  

   Though 
  mature 
  animals 
  were 
  abundant 
  in 
  summer, 
  the 
  

   extreme 
  heat 
  prevented 
  success 
  in 
  this 
  respect 
  in 
  the 
  confined 
  

   vessels, 
  especially 
  after 
  the 
  long 
  journey 
  from 
  the 
  sea-coast, 
  

   while 
  those 
  with 
  the 
  reproductive 
  elements 
  developed 
  late 
  in 
  

   autumn 
  failed 
  to 
  afford 
  a 
  single 
  embryo 
  J. 
  As 
  previously 
  

   indicated, 
  M. 
  Claparede 
  found 
  a 
  developing 
  form 
  which 
  he 
  

  

  * 
  Ana. 
  & 
  Mag. 
  Nat. 
  Hist. 
  4th 
  ser. 
  vol. 
  xiii. 
  p. 
  201. 
  

  

  t 
  Op. 
  cit. 
  p. 
  260. 
  

  

  \ 
  The 
  surface 
  of 
  the 
  sea 
  was 
  examined 
  by 
  the 
  towing-net 
  from 
  the 
  

   margin 
  of 
  full 
  tide 
  outward 
  for 
  several 
  miles 
  in 
  September, 
  but 
  no 
  larval 
  

   type 
  connected 
  with 
  this 
  form 
  was 
  obtained. 
  In 
  subsequent 
  years, 
  how- 
  

   ever, 
  all 
  stages 
  have 
  been 
  procured 
  at 
  St. 
  Andrews. 
  

  

  