182 
Sponges, 
f  Asn.  Jour.  Pharnor 
\      Apra,  1881. 
SPONGES. 
Sponges  iDresent  a  point  still  somewhat  problematical  as  to  their  true- 
l^osition  in  the  scale  of  animal  life,  and  there  are  still  many  doubtful  or 
imperfectly  known  facts  pertaining  to  their  organization.  As  a  family „, 
sponges  are  very  remarkable  for  the  lack  of  a  definite  and  constant  form, 
have  various  habits  of  growth,  are  insensible  to  irritation  and  powerless  to 
move  about.  The  known  species  number  now  about  three  hundred,  and 
new  ones  are  constantly  observed,  in  view  of  which  fact  it  is  obviously 
impossible  to  describe,  within  the  limits  of  this  sketch,  more  than  the 
jirominent  characteristics  of  the  type.  The  description  following  may  be 
referred  more  particularly  to  the  sponges  of  commerce. 
Milne-Edwards  and  others  have  considered  each  sponge  as  one  separate 
and  distinct  individual ;  but  Prof.  Clarke,  Dr.  Lockwood,  Prof.  Grant  and 
others,  regard  them  as  an  aggregation  of  minute  infusoria,  each  within  its 
living  cell,  and  they  are  considered  to  begin  life  as  solitary  animalcules, 
and  only  in  associations  of  these  does  the  characteristic  sponge  structure 
appear.  Of  course  this  reduces  it  still  lower  in  the  plane  of  animal  life, 
because  individuality  is  soon  lost  when  many  of  the  same  species  are 
brought  together  and  coalesce.  The  mass  then  may  be  considered  in  its 
complete  state  as  being  composed  of  three  parts,  namely,  the  skeleton, 
known,  when  cleansed,  to  commerce  as  the  sponge;  fhe  fleshy  matter,  by 
which  this  is  surrounded  ;  and  third,  the  spicules,  or  little  spines,  by  which 
the  fleshy  matter  is  held  in  place. 
The  skeleton  is  a  fibrous  mass  of  complicated  network  of  more  or  less 
regularity  in  the  meshes,  and  of  different  patterns  in  the  various  species. 
The  fibre  appears  solid  under  the  microscope,  but  in  some  species  at  least 
it  contains  within  its  interior  another  cylindrical  thread,  which  usually 
becomes  elegantly  wavy  or  spiral  under  flexion,  and  probably  adds  to  the 
elasticity.  In  some  the  skeleton  is  soft,  compressible  and  very  bibulous,, 
from  which  there  is  a  gradual  passage  into  those  of  a  rigid  and  compact 
texture,  sometimes  friable.  The  first  are  composed  of  a  horny  substance, 
and  the  varying  excess  of  silicious  or  calcareous  matter  causes  it  to  lose 
more  or  less  elasticity,  and  impairs  its  usefulness.  As  the  skeleton  is 
secreted  by  the  fleshy  mass  of  the  animal,  which  is  an  active  eliminator  of 
the  salt  of  the  ocean,  it  is  attempted  to  group  them  upon  considerations  of 
their  building  propensities,  and  the  toilet  and  domestic  sponges  generally 
affecting  horn,  or  keratose,  are  grouj)ed  as  "keratora."  With  an  excess  of 
lime,  as  calccirea,  building  with  silex — silicea.  Various  varieties  exhibit 
all  the  colors,  and  many  are,  while  alive,  very  brilliant  in  appearance.. 
Examining  a  toilet  sponge,  we  find  that  the  framework  is  covered  with  a 
membrane  (not  universal  with  all  species),  thin  above,  deep-brown  on  the 
sides  and  yellowish-brown  towards  the  base.  This  investing  membrane 
exhibits  larger  and  smaller  openings,  is  not  spread  smoothly,  but  appears 
irregularly  covered  with  conical  shaped  points.  Making  a  section  of  the 
still  living  sponge,  we  find  the  skeleton  embedded  in  a  glairy,  gelatinous 
or  albuminous  substance,  about  the  consistency  of  raw  beef,  with  an 
exuding  viscous,  yellowish  clear  brown  (in  the  bath  sponge  a  clear  gray) 
