334 
TOUCHINa  SPONGES. 
clothed  with  a  soft  flesh,  which,  when  examined  with  a  powerful 
microscope,  is  found  to  consist  of  an  aggregation  of  amoeba-like 
bodies,  some  of  which  are  furnished  with  long  cilia  (hair-like 
appendages)  by  the  agency  of  which  a  current  of  water  is  kept 
up  through  the  passages  and  canals  excavated  in  the  substance 
of  the  mass.  From  observations  which  have  been  made  upon 
the  early  development  of  sponges,  it  appears  that  they  begin  life 
as  solitary  amoebae,  and  it  is  only  in  the  midst  of  aggregations 
formed  by  the  multiplication  of  these  that  the  characteristic 
sponge  structure  makes  its  appearance  ;  the  formation  of  spicules 
being  the  first  indication  of  such  orgtmization.  The  ciliated  cells 
seem  to  form  the  walls  of  the  canals  by  which  the  whole  fabric 
of  the  sponge  is  traversed.  These  canals,  which  are  very  irregu- 
lar in  their  distribution,  may  be  said  to  commence  in  the  small 
pores  of  the  surface,  and  to  terminate  in  large  vents  ;  and  a 
current  is  continually  entering  at  the  former  and  passing  forth 
from  the  latter  during  the  whole  life  of  the  sponge,  bringing  in 
alimentary  particles  and  oxygen,  and  carrying  out  refuse  matter. 
The  skeleton,  which  gives  shape  and  substance  to  the  mass  of 
sarcode  particles  that  constitute  the  living  animal,  is  composed, 
in  the  sponges  with  which  we  are  most  familiar,  of  an  irregular 
reticulation  of  fibres.  Most  sponges  are  strengthened  by  cal- 
careous or  siliceous  spicules,  and  the  variety  of  forms  presented 
by  these  bodies  is  almost  endless.  In  the  ordinary  sponge, 
Spongia  offioinalis,  the  fibrous  skeleton  is  almost  entirely  destitute 
of  spicules ;  but  in  the  curious  and  beautiful  Dictyochalix 
pumiceus  of  Barbadoes,  the  entire  network  of  fibres  is  composed 
of  silex,  and  is  so  transparent  that  it  looks  as  if  composed  of 
spun  glass. 
With  the  exception  of  those  that  belong  to  the  genus  SpongiUa, 
all  known  sponges  are  marine,  but  they  differ  very  much  in  habit 
of  growth ;  some  are  only  found  at  considerable  depths,  others 
live  near  the  surface,  and  many  attach  themselves  to  rocks  and 
shells  between  the  tide-marks.  The  average  depth  at  which 
the  best  Turkey  sponges  are  found  is  thirty  fathoms  ;  those  of 
an  inferior  quality  are  found  at  lesser  depths. — Chemist  and 
Druggist,  Jan.  1861. 
