184 
Sjmiges. 
r  Am.  Jour.  Pliarm. 
I       April,  1881. 
Prof.  Grant  first  observed  closely  the  ceaceless  fiovv'^  of  liquid  matter 
through  and  out  of  the  living  si)onge.  Another  discussion  has  been  had 
over  the  manner  in  which  this  is  caused  or  maintained.  Dutrochet,  hav- 
ing made  his  celebrated  discovery  of  that  law  of  endosmose  whicli  regu- 
lates the  transmission  of  fluids  of  unequal  densities  through  organic  mem- 
branes, was  perhaps  biased  or  prejudiced  in  applying  the  same  law  to  the 
solution  of  this  2)roblem.  At  any  rate,  naturalists  now  agree  that  the  flow 
is  produced  by  the  lashes  or  cilia,  with  which  the  unnumbered  animalcules 
are  each  provided.  The  little  chamber  into  which  the  pore  opens  has  its 
wall  lined  with  these  uniciliated  cells,  and  each  lashes  its  cilium  with  vigor, 
and  all  harmoniously  downward  and  inward,  the  effect  vacuum  above,  the 
water,  of  course,  passing  in,  being  carried  through  the  ramifications  and 
out  of  the  oscula  with  some  vigor.  Hurled  along  in  the  liquid  are  opaque 
masses,  composed  of  excrementous  particles,  and  at  certain  seasons  ova  and 
germicules,  from  whicli  new  beings  are  produced.    We  may  consider  the 
sponge  mass  as  having  a  complete  assimilating 
or  digestive  apparatus.  The  cells,  or  some  of  them, 
probably  act  as  stomachal  sacs,  with  the  lashes  for 
motors  to  attract  food  and  repel  refuse  after  the  • 
extracrion  of  nourishment,  which  latter  probably 
passes  through  the  gelatinous  mass  into  the  gen^ 
eral  development.  The  sj^onge  has  such  remark- 
able recuperative  powers  that  one,  being  cut  while 
alive,  quickly  rejoins,  though  not  replaced  in  the 
Fig.  2 — Living  sponges,  same  position.  We  show  in  Fig.  2  a  group  of  liv- 
ing sponges. 
Perhaps  the  most  curious  parts  of  the  sponge  structure  are  the  spieula,  or 
little  spines,  shown  in  Fig.  3.  These,  embedded  in  all  parts  of  the  sarcode, 
.serve  to  bind  the  tissueless  flesh  in  form.  They  serve  as  a  natural  felting, 
or  as  tiny  anchors,  generally  composed  of  silex  or  lime,  and  are  of  an  infi- 
nite variety  of  shapes,  sometimes  occurring  seimrately  and  sometimes  in 
bundles,  generally  in  this  case  bound  together  with  horny  matter.  The 
spicules  of  the  "sheep's  wool"  are  of  the  latter  class,  and  under  a  low  mag- 
aiifying  power  will  be  found  generally  broken  and  frayed.  Spicules  of 
silex  are  the  most  common  and  most  variable  in  shape,  and  present  every 
gradation,  from  sinijile  needle  to  many-pointed  star.  Spicules  of  the  same 
material,  but  of  various  forms,  are  found  in  the  same  sponge,  but  seem  to 
occupy  certain  definite  positions— some  are  peculiar  to  crust,  some  to  sar- 
code and  others  to  margins  of  canals,  etc.  They  cannot  be  considered  as 
formed  by  crystallization,  as  many  could  not  so  be  jjroduced;  they  exhibit 
more  or  less  of  a  central  cavity,  in  some  of  which  organic  matter  has  been 
discovered.  Being  beautiful  microscopic  objects,  they  have  excited  much 
attention,  especially  as  they  are  the  most  lasting  parts  of  the  structure,  and 
are  distributed  not  only  over  every  known  sea,  being  constantly  dredged 
from  the  greatest  depths,  but  they  also  in  a  large  measure,  in  connection 
with  other  silicious  bodies  of  like  insignificance,  go  to  form  many  large 
portions  of  the  earth's  surface.  They  occur  in  guano  deposits,  largely  in 
the  chalk  formations,  also  in  the  tertiary  formations  in  England,  etc. 
Sponge  tissue  may  often  be  observed  in  sections  of  agate,  chalcedony,  etc. 
