﻿76 
  Mr. 
  A. 
  Dendy 
  on 
  Sponges 
  from 
  

  

  tinuity 
  of 
  the 
  surface 
  is 
  interrupted 
  at 
  irregular 
  intervals 
  

   by 
  a 
  number 
  of 
  pits 
  or 
  depressions, 
  which 
  form 
  a 
  very 
  con- 
  

   spicuous 
  external 
  character. 
  Some 
  of 
  the 
  pits 
  are 
  shallow 
  

   and 
  hemispherical, 
  others 
  deep 
  and 
  tubular 
  ; 
  some 
  have 
  in 
  

   their 
  floor 
  the 
  evident 
  openings 
  of 
  a 
  number 
  of 
  oscular 
  tubes, 
  

   while 
  others 
  are 
  lined 
  by 
  a 
  smooth 
  continuous 
  membrane 
  

   which 
  presents 
  no 
  openings 
  to 
  the 
  naked 
  eye. 
  In 
  sections 
  

   the 
  floor 
  of 
  a 
  pit 
  is 
  sometimes 
  seen 
  to 
  be 
  perforated 
  by 
  a 
  

   number 
  of 
  very 
  small 
  pores, 
  which 
  are 
  doubtless 
  inhalant. 
  I 
  

   have 
  not 
  been 
  able 
  to 
  work 
  out 
  in 
  detail 
  the 
  arrangement 
  of 
  

   the 
  pores 
  and 
  oscula 
  ; 
  but 
  from 
  the 
  examination 
  of 
  my 
  sections 
  

   I 
  have 
  come 
  to 
  the 
  conclusion 
  that 
  some 
  of 
  the 
  surface-pits 
  

   are 
  localized 
  pore-areas, 
  while 
  others 
  are 
  oscular 
  areas. 
  This 
  

   condition 
  recalls 
  that 
  described 
  by 
  Professor 
  Sollas 
  in 
  his 
  

   Cinachyra 
  barbata 
  * 
  ; 
  but 
  further 
  investigations 
  are 
  required 
  

   to 
  enable 
  one 
  to 
  say 
  how 
  far 
  the 
  resemblance 
  holds 
  good 
  ; 
  in 
  

   any 
  case 
  the 
  two 
  species 
  appear 
  to 
  be 
  quite 
  distinct, 
  and 
  the 
  

   arrangement 
  of 
  the 
  oscula, 
  although 
  in 
  both 
  they 
  are 
  con- 
  

   fined 
  to 
  special 
  pits 
  on 
  the 
  surface, 
  appears 
  to 
  be 
  different 
  in 
  

   the 
  two 
  cases. 
  

  

  The 
  skeleton 
  of 
  the 
  sponge 
  is 
  arranged 
  in 
  a 
  perfectly 
  

   typical 
  radiate 
  manner, 
  the 
  stout 
  radiating 
  fibres 
  all 
  starting 
  

   from 
  a 
  dense 
  central 
  nucleus. 
  There 
  is 
  no 
  special 
  cortical 
  

   skeleton 
  of 
  radiately 
  disposed 
  oxea, 
  such 
  as 
  occurs 
  in 
  Cina- 
  

   chyra. 
  

  

  Spicules. 
  — 
  («). 
  Megasclera 
  : 
  — 
  (1) 
  Very 
  long, 
  fusiform, 
  

   straight 
  oxea, 
  tapering 
  very 
  gradually 
  to 
  a 
  fine 
  point 
  at 
  each 
  

   end 
  ; 
  size 
  about 
  3*5 
  by 
  0*042 
  millim. 
  (2) 
  Protriasnes, 
  with 
  

   very 
  long 
  and 
  very 
  slender 
  shaft 
  and 
  rather 
  short, 
  sharp- 
  

   pointed 
  cladi 
  ; 
  length 
  of 
  shaft 
  in 
  a 
  well-developed 
  example 
  

   about 
  0*46 
  millim., 
  diameter 
  about 
  0*014 
  millim. 
  ; 
  length 
  of 
  

   cladi 
  about 
  0*041) 
  millim., 
  diameter 
  at 
  base 
  about 
  0*007 
  

   millim. 
  These 
  spicules 
  are 
  often 
  of 
  hair-like 
  dimensions. 
  

   (3) 
  Anatriames, 
  with 
  shaft 
  perhaps 
  somewhat 
  shorter 
  than 
  

   that 
  of 
  the 
  protriame 
  and 
  often 
  of 
  hair-like 
  thinness. 
  

  

  {b). 
  Microsclera 
  : 
  — 
  Very 
  small 
  slender 
  sigmaspires, 
  about 
  

   0022 
  millim. 
  long. 
  

  

  Concerning 
  the 
  details 
  of 
  the 
  histology 
  and 
  canal-system 
  of 
  

   this 
  sponge 
  1 
  am 
  not 
  able 
  to 
  give 
  much 
  information. 
  It 
  is 
  

   difficult 
  to 
  work 
  out, 
  owing 
  to 
  the 
  great 
  development 
  of 
  

   spicules, 
  and 
  1 
  have 
  only 
  the 
  smaller 
  of 
  the 
  two 
  specimens 
  at 
  

   my 
  disposal. 
  The 
  ectosome 
  is 
  fairly 
  thick 
  and 
  gelatinous, 
  

   with 
  a 
  tendency 
  to 
  become 
  fibrous. 
  The 
  choanosome 
  presents 
  

  

  * 
  Report 
  on 
  the 
  Tetractinellida 
  of 
  the 
  'Challenger' 
  Expedition, 
  

   p. 
  23. 
  

  

  