﻿90 
  Mr. 
  A. 
  Dendy 
  on 
  Sponges 
  from 
  

  

  column, 
  and 
  it 
  will 
  be 
  evident 
  from 
  the 
  figure 
  (fig. 
  11) 
  that 
  

   the 
  columns 
  are 
  not 
  very 
  well-defined 
  structures. 
  

  

  Spicules. 
  — 
  These 
  are 
  of 
  two 
  kinds 
  : 
  — 
  (1) 
  Large 
  smooth 
  

   styli, 
  more 
  or 
  less 
  curved, 
  especially 
  towards 
  the 
  well-rounded 
  

   base, 
  which 
  is 
  sometimes 
  slightly 
  swollen 
  ; 
  gradually 
  sharp- 
  

   pointed 
  at 
  the 
  apex 
  ; 
  size 
  when 
  fully 
  developed 
  about 
  0"38 
  

   by 
  - 
  014 
  millim. 
  (2) 
  Small 
  tylostyli, 
  straight 
  or 
  bent 
  near 
  

   the 
  base 
  ; 
  with 
  small 
  subglobular 
  heads 
  and 
  very 
  gradually 
  

   sharp-pointed 
  at 
  the 
  apex 
  ; 
  usually 
  more 
  or 
  less 
  covered 
  with 
  

   minute 
  spines, 
  which 
  appear, 
  however, 
  to 
  be 
  always 
  absent 
  

   from 
  the 
  base. 
  These 
  spicules 
  when 
  full-grown 
  average 
  

   in 
  size 
  about 
  0119 
  by 
  O004 
  millim., 
  the 
  diameter 
  being 
  

   measured 
  just 
  above 
  the 
  head. 
  It 
  is 
  unnecessary 
  to 
  give 
  

   figures 
  of 
  these 
  spicules, 
  as 
  this 
  has 
  already 
  been 
  clone 
  by 
  

   Dr. 
  Bowerbank 
  (loc. 
  cit.). 
  

  

  This 
  sponge 
  is 
  remarkable 
  for 
  the 
  presence 
  in 
  all 
  specimens 
  

   of 
  numerous 
  commensal 
  worms. 
  The 
  worms 
  are 
  very 
  small 
  

   tubicolous 
  Oligochajtes. 
  Their 
  tubes 
  (fig. 
  11, 
  a, 
  5, 
  c) 
  are 
  

   very 
  slender, 
  averaging 
  about 
  0*3 
  millim. 
  in 
  diameter, 
  and 
  

   they 
  radiate 
  towards 
  the 
  surface 
  of 
  the 
  sponge, 
  opening 
  about 
  

   at 
  the 
  level 
  of 
  the 
  dermal 
  membrane, 
  in 
  which 
  they 
  appear 
  as 
  

   minute 
  circular 
  pits 
  easily 
  visible 
  when 
  the 
  surface 
  of 
  the 
  

   sponge 
  is 
  examined 
  with 
  a 
  hand-lens. 
  Sometimes 
  the 
  mar- 
  

   gins 
  of 
  the 
  tubes 
  are 
  a 
  little 
  raised, 
  and 
  the 
  tubes 
  usually 
  

   appear 
  close 
  to 
  the 
  sides 
  of 
  the 
  radiating 
  skeleton 
  columns. 
  

   Fig. 
  11 
  shows 
  portions 
  of 
  three 
  of 
  the 
  worm 
  -tubes, 
  one 
  of 
  

   them 
  (a) 
  opening 
  close 
  to 
  a 
  surface- 
  papilla 
  and 
  still 
  containing 
  

   the 
  worm. 
  The 
  tubes 
  sometimes 
  branch 
  ; 
  but 
  whether 
  or 
  not 
  

   the 
  worm 
  likewise 
  does 
  so 
  I 
  have 
  been 
  unable 
  to 
  determine. 
  

   It 
  is 
  very 
  possible 
  that 
  the 
  presence 
  of 
  these 
  commensal 
  worms 
  

   has 
  a 
  good 
  deal 
  to 
  do 
  with 
  the 
  characteristic 
  globular 
  shape 
  

   of 
  the 
  sponge, 
  and 
  one 
  might 
  almost 
  regard 
  the 
  whole 
  struc- 
  

   ture 
  as 
  a 
  spherical 
  mass 
  of 
  racliately 
  arranged 
  tubicolous 
  

   worms 
  in 
  which 
  the 
  interstices 
  between 
  the 
  individual 
  tubes 
  

   are 
  occupied 
  by 
  a 
  sponge. 
  It 
  would 
  be 
  interesting 
  to 
  know 
  

   whether 
  the 
  worm 
  and 
  the 
  sponge 
  ever 
  live 
  separately 
  or 
  are 
  

   always 
  associated 
  together. 
  

  

  The 
  worm-tubes 
  are 
  also 
  present 
  in 
  Dr. 
  Bowerbank's 
  type 
  

   of 
  the 
  species, 
  of 
  which 
  I 
  made 
  a 
  careful 
  examination 
  in 
  the 
  

   British 
  Museum 
  ; 
  but 
  he 
  laboured 
  under 
  a 
  curious 
  mistake 
  

   as 
  to 
  their 
  true 
  nature, 
  regarding 
  them 
  as 
  a 
  tubular 
  skeleton 
  

   proper 
  to 
  the 
  sponge. 
  This 
  mistaken 
  idea 
  led 
  him 
  to 
  give 
  

   a 
  most 
  remarkable 
  account 
  of 
  the 
  species, 
  for 
  which 
  I 
  would 
  

   refer 
  the 
  reader 
  to 
  his 
  original 
  paper 
  *, 
  as 
  I 
  have 
  not 
  space 
  to 
  

   quote 
  it 
  in 
  this 
  place. 
  

  

  * 
  Loc. 
  dt. 
  

  

  