﻿A 
  MONOGBAPH 
  OF 
  THE 
  VICTORIAN 
  SPONGES. 
  13 
  

  

  spherical 
  nucleus, 
  about 
  0-0025 
  mm. 
  in 
  diameter, 
  around 
  which 
  is 
  aggregated 
  a 
  

   small 
  body 
  of 
  granular 
  protoplasm 
  running 
  out 
  in 
  various 
  directions 
  into 
  long, 
  thread- 
  

   like 
  processes. 
  Adjacent 
  cells 
  are 
  united 
  together 
  by 
  these 
  processes 
  so 
  as 
  to 
  form 
  a 
  

   network, 
  as 
  in 
  higher 
  sponges. 
  Similar 
  cells 
  are 
  shown 
  in 
  the 
  case 
  of 
  Leiicosoleuia 
  

   cavata 
  on 
  PI. 
  VI., 
  Figs. 
  4, 
  5. 
  

  

  We 
  may 
  mention 
  here 
  a 
  very 
  remarkable 
  development 
  of 
  the 
  stellate 
  connec- 
  

   tive 
  tissue 
  cells 
  which 
  takes 
  place 
  in 
  Leucosolcnin 
  pvoxima. 
  In 
  this 
  si)onge 
  the 
  cells 
  

   in 
  question, 
  instead 
  of 
  all 
  remaining 
  embedded 
  in 
  the 
  gelatinous 
  ground-substance 
  

   between 
  tlie 
  ectoderm 
  and 
  endoderm 
  in 
  the 
  normal 
  manner, 
  have 
  grown 
  out 
  l)etween 
  

   tlie 
  collared 
  cells 
  of 
  the 
  endoderm 
  into 
  the 
  gastral 
  cavity, 
  where 
  they 
  foi'in 
  a 
  delicate 
  

   network, 
  as 
  shown 
  on 
  PI. 
  VIII., 
  Fig. 
  2. 
  The 
  cells 
  composing 
  this 
  network 
  are 
  of 
  very 
  

   large 
  size, 
  but 
  otherwise 
  do 
  not 
  differ 
  from 
  normal 
  multipolar 
  mesoderm 
  cells. 
  They 
  

   are 
  nucleated 
  and 
  around 
  the 
  nucleus 
  are 
  a 
  number 
  of 
  granules. 
  Some 
  of 
  the 
  proto- 
  

   plasmic 
  processes 
  of 
  the 
  cells 
  retain 
  connection 
  with 
  the 
  mesoderm 
  of 
  the 
  tube-wall, 
  

   tbus 
  supporting 
  the 
  network 
  in 
  the 
  gastral 
  cavity. 
  Such 
  an 
  extraordinary 
  develop- 
  

   ment 
  of 
  tlie 
  mesoderm 
  seems 
  almost 
  incredible, 
  but 
  it 
  is 
  far 
  too 
  distinct 
  and 
  oljvious 
  

   in 
  my 
  numerous 
  sections 
  of 
  the 
  sponge 
  in 
  question 
  to 
  admit 
  of 
  any 
  doubt 
  ; 
  moreover 
  

   it 
  leads 
  on 
  to 
  a 
  still 
  further 
  develo])ment 
  in 
  the 
  same 
  direction 
  in 
  an 
  allied 
  species 
  

   {Leucosolenia 
  wilsoni), 
  which 
  will 
  be 
  fully 
  described 
  in 
  dealing 
  with 
  the 
  canal 
  

   system. 
  

  

  (2.) 
  The 
  Amcchnicl 
  Cells 
  (" 
  Wanderzellen 
  " 
  of 
  German 
  authors) 
  are 
  difficult 
  to 
  

   distinguish 
  from 
  tlie 
  ordinary 
  stellate 
  ones, 
  closely 
  resembling 
  the 
  latter 
  with 
  the 
  

   long 
  processes 
  cut 
  off. 
  They 
  are 
  somewhat 
  more 
  massive 
  and 
  rounded 
  in 
  outline. 
  

  

  (3.) 
  I 
  am 
  not 
  able 
  to 
  state 
  with 
  certainty 
  whether 
  or 
  not 
  sub-dermal 
  Gland 
  Cells 
  

   occur 
  in 
  the 
  Ilomocmla. 
  In 
  Leucosolenia 
  ventricosa, 
  however, 
  I 
  have 
  found 
  certain 
  

   elements 
  resembling 
  to 
  a 
  great 
  extent 
  the 
  sub-dermal 
  gland 
  cells 
  described 
  by 
  me* 
  

   in 
  Granlia 
  labyriuthica, 
  but 
  I 
  do 
  not 
  venture 
  to 
  express 
  a 
  definite 
  opinion 
  as 
  to 
  their 
  

   nature. 
  

  

  (4.) 
  In 
  some 
  cases 
  certain 
  of 
  the 
  mesodermal 
  ch'iiienls 
  b(>come 
  specially 
  

   modified 
  to 
  form 
  more 
  or 
  less 
  plate-like 
  Endothelial 
  Cells. 
  These 
  occur 
  in 
  two 
  distinct 
  

   situations 
  and 
  differ 
  in 
  character 
  accordingly. 
  The 
  two 
  kinds 
  of 
  mesodennal 
  

   pavement 
  cells 
  (cndotlielial 
  cells) 
  wliicli 
  T 
  liave 
  as 
  yet 
  met 
  with 
  in 
  the 
  group 
  ai'c 
  

   (a) 
  the 
  lining 
  cells 
  of 
  the 
  embryo-containing 
  cavities 
  and 
  (l>) 
  iho 
  cells 
  wliidi 
  

   ensheath 
  the 
  sjiicule-rays 
  projecting 
  into 
  the 
  gastral 
  cavity. 
  

  

  I 
  have 
  shown 
  elsewhere 
  | 
  that 
  in 
  Stelospongos 
  the 
  developing 
  embr)'os 
  are 
  lodged 
  in 
  

   special 
  cavities, 
  excavated, 
  as 
  it 
  were, 
  in 
  the 
  substance 
  of 
  the 
  mesodenn, 
  and 
  that 
  

  

  • 
  " 
  Stndipfl 
  on 
  the 
  Compnmtivo 
  Anatomy 
  of 
  HpnnRrs, 
  HI.," 
  iVrc. 
  loc. 
  cit. 
  

   t 
  " 
  Stutlie3 
  on 
  the 
  Coniiiaiativo 
  Anatomy 
  of 
  Spongos, 
  II.," 
  Ac. 
  he. 
  cit. 
  

  

  