﻿SPONGIIDA. 
  

  

  369 
  

  

  Di/sidea, 
  Fotrochota, 
  Rhaj)hidophli(s, 
  AcantJiella). 
  In 
  the 
  systematic 
  

   descriptions 
  of 
  the 
  genera 
  and 
  species 
  I 
  have 
  employed 
  the 
  old 
  

   expression 
  " 
  sarcode 
  " 
  for 
  the 
  soft 
  tissues 
  generally, 
  as 
  being^ 
  intel- 
  

   ligible, 
  comprehensive, 
  and 
  as 
  having 
  the 
  advantage 
  of 
  involving 
  no 
  

   special 
  theory 
  or 
  view 
  with 
  regard 
  to 
  the 
  homologies 
  of 
  the 
  parts 
  

   referred 
  to 
  ; 
  the 
  greater 
  part 
  of 
  the 
  tissues 
  included 
  under 
  the 
  term 
  

   are, 
  however, 
  the 
  " 
  mesoderm 
  " 
  of 
  F. 
  E. 
  Schulze, 
  together 
  with 
  the 
  

   ciliated 
  chambers 
  and 
  the 
  walls 
  of 
  the 
  canal-system 
  which 
  it 
  

   encloses. 
  

  

  IiuUvidiml 
  Variation. 
  — 
  A 
  few 
  remarks 
  on 
  this 
  subject 
  are 
  sug- 
  

   gested 
  by 
  the 
  study 
  of 
  this 
  large 
  collection. 
  First, 
  variation 
  in 
  the 
  

   size 
  of 
  spicules 
  is 
  an 
  almost 
  invariable 
  occurrence 
  in 
  different 
  speci- 
  

   mens 
  of 
  the 
  same 
  species, 
  as 
  it 
  is 
  in 
  individual 
  spicules 
  in 
  the 
  same 
  

   specimen 
  ; 
  in 
  the 
  one 
  ease, 
  however, 
  it 
  rightly 
  falls 
  under 
  the 
  head 
  of 
  

   variation, 
  in 
  the 
  latter 
  chiefly 
  under 
  that 
  of 
  gruivth. 
  In 
  the 
  descrip- 
  

   tions 
  below 
  will 
  be 
  found 
  statements 
  which 
  show 
  the 
  range 
  of 
  this 
  

   form 
  of 
  variation 
  within 
  the 
  limits 
  of 
  a 
  species 
  to 
  be 
  frequently 
  

   wide, 
  see 
  especially 
  Lencophloeus 
  fenestratus, 
  Echinodictijum 
  (the 
  

   spined 
  spicule), 
  and 
  Stelletta 
  purpurea. 
  The 
  Ectyonida3 
  exhibit, 
  

   as 
  a 
  rule, 
  surprisingly 
  little 
  variation 
  of 
  this 
  kind, 
  and 
  little 
  use 
  is 
  

   to 
  be 
  made 
  of 
  characters 
  based 
  on 
  size 
  in 
  distinguishing 
  even 
  species 
  

   in 
  this 
  group. 
  Chalinida? 
  and 
  Desmacidinidse 
  are 
  also 
  very 
  fairly 
  

   constant 
  as 
  a 
  rule. 
  Secondly, 
  variation 
  in 
  the 
  form 
  of 
  spicules 
  is 
  

   less 
  common. 
  The 
  Suberitidas 
  exhibit 
  variation 
  of 
  the 
  head 
  of 
  the 
  

   skeleton-spicule 
  from 
  sub-acuate 
  to 
  spinulate 
  (Suberites). 
  Modifi- 
  

   cations 
  of 
  the 
  form 
  of 
  the 
  ends 
  of 
  acerate 
  spicules 
  are 
  certainly 
  not 
  

   often 
  to 
  be 
  noticed 
  ; 
  but 
  this 
  collection 
  shows 
  that 
  in 
  Pellina 
  muricata 
  

   the 
  ends 
  of 
  the 
  acerate 
  vary 
  from 
  being 
  gradually 
  sharply 
  pointed 
  

   to 
  being 
  rounded 
  off 
  almost 
  as 
  thoroughly 
  as 
  in 
  the 
  usual 
  " 
  cylin- 
  

   drical 
  ; 
  " 
  and 
  in 
  Cladocludina 
  nuda 
  the 
  ends 
  may 
  taper 
  gardually 
  

   from 
  about 
  four 
  diameters 
  from 
  end 
  of 
  spicule, 
  or 
  else 
  from 
  within 
  

   about 
  1| 
  diameters 
  (var. 
  ahruptispicula 
  , 
  mihi), 
  producing 
  a 
  very 
  

   different 
  appearance. 
  Thirdly, 
  as 
  to 
  variation 
  in 
  the 
  e.vtemal 
  form 
  

   of 
  the 
  Sponge 
  within 
  the 
  limits 
  of 
  the 
  same 
  species, 
  striking 
  ex- 
  

   amples 
  are 
  afforded 
  by 
  the 
  series 
  oi 
  lotrochota, 
  purpurea 
  and 
  Clathria 
  

   reimvardti 
  (where 
  a 
  multi-personal 
  origin 
  appears 
  to 
  explain 
  the 
  most 
  

   remarkable 
  case). 
  The 
  number 
  of 
  vents 
  present 
  has 
  been 
  used 
  as 
  a 
  

   generic 
  character 
  in 
  the 
  Tetractinellida 
  by 
  Prof. 
  Sollas 
  [Geodia, 
  

   hops). 
  In 
  one 
  of 
  the 
  species 
  of 
  Stelletta 
  here 
  described 
  this 
  seems 
  

   to 
  be 
  constant, 
  in 
  the 
  other 
  not 
  ; 
  in 
  the 
  species 
  of 
  Geodia 
  described 
  

   below 
  it 
  is 
  doubtful 
  whether 
  absence 
  of 
  vents 
  (" 
  lipostomy," 
  HdcJcel) 
  

   is 
  constant. 
  

  

  '■'■ 
  Person" 
  -tJieory. 
  — 
  The 
  individuality 
  of 
  those 
  parts 
  of 
  a 
  Sponge 
  

   which 
  enclose 
  a 
  single 
  cloacal 
  cavity 
  seems 
  to 
  be 
  regarded 
  as 
  a 
  fact 
  

   by 
  Marshall, 
  who 
  speaks 
  (Zeitschr. 
  wiss. 
  Zool. 
  xxxv. 
  p. 
  98 
  &c.) 
  of 
  

   species 
  of 
  Dysideidaj 
  as 
  being 
  "monozoisch" 
  or 
  " 
  polyzoiseh." 
  It 
  is 
  

   difficult 
  to 
  see 
  how 
  the 
  different 
  cloacal 
  tubes 
  which 
  are 
  formed 
  

   during 
  adult 
  life 
  by 
  folding-over 
  of 
  a 
  flat 
  wall, 
  as 
  appears 
  to 
  be 
  the 
  

   case 
  in 
  the 
  species 
  named 
  below 
  , 
  Si 
  phonochalina 
  Jndlata 
  and 
  Dysidea 
  

   semicanalis, 
  can 
  be 
  said 
  to 
  constitute 
  individuals. 
  It 
  seems 
  possible 
  

  

  2b 
  

  

  