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ME.  E.  WETHERED  ON  THE  MICROSCOPIC  [May  1893.. 
In  fig.  1  we  have  a  spherule  with  a  fragment  of  a  polyzoan  as  a 
nucleus ;  this  is  in  part  surrounded,  or  encrusted,  by  a  stratum  of 
tubules  measuring  *03  millim.  in  diameter.  These  are  again  enclosed 
by  an  outer  stratum  (which  envelops  the  whole  inuer  stratum  and 
the  nucleus)  of  well-defined  tubules  measuring  -14  millim.  in 
diameter. 
In  fig.  2  we  have  a  spherule  containing  a  nucleus,  the  nature  of 
which  is  not  apparent,  surrounded  by  tubules  measuring  TO  millim. 
in  diameter.  These  are  very  like  the  larger  tubules  in  fig.  1,  hut 
the  smaller  forms  are  not  represented.  The  interiors  of  the  tubules 
are  filled  in  with  calcite,  against  which  the  walls  stand  out  in  relief. 
In  fig.  3  a  very  interesting  spherule  is  depicted.  Here  are  two 
strata  of  tubules  which  are  to  some  extent  divided  by  finely- 
granulated  material.  The  tubules  included  in  the  inner  stratum 
average  about  -02  millim.  in  diameter,  while  those  in  the  outer 
average  -05  millim. ;  the  latter  are  therefore  the  larger  of  the  two. 
The  tubules  in  the  inner  stratum  are  not  continuous  around  the 
entire  nucleus,  but  pass  into  finely-granulated  material,  in  which 
only  obscure  and  occasional  outlines  of  tubules,  and  streaks  and 
spots  of  calcite  can  he  detected.  At  first  sight,  I  thought  this 
finely-granulated  material  was  of  organic  origin,  but  after  further 
examination  I  have  come  to  the  conclusion  that  there  is  doubt  as  to 
this.  I  am  disposed  to  regard  the  granulated  material  as  a  calca¬ 
reous  residuum,  proceeding  from  the  decay  of  those  tubules  which 
have  not  been  preserved  by  the  infilling  of  calcite.  This  explana¬ 
tion,  however,  does  not  account  for  the  difference  in  size  of  the 
tubules  in  the  two  ‘  strata.’  There  are  two  possible  explanations 
of  the  occurrence : — (a)  That  the  smaller  forms  are  the  same  as  the 
larger,  but  of  younger  growth  ;  (6)  That  the  two  sets  of  tubules 
have  no  relation  one  with  the  other.  That  is  to  say,  the  inner 
stratum  first  formed  a  spherule  around  the  original  nucleus,  and 
later  on  this  first  spherule  became  the  nucleus  for  the  outer  set  of 
tubules.  If  the  first  explanation  he  the  right  one,  then,  I  think, 
we  ought  to  find  the  order  of  the  6  strata  ’  reversed ;  that  is  to  say, 
the  smaller  tubules,  as  the  younger,  would  be  in  the  outer  or  more 
recent  stratum,  and  the  larger  or  older  tubules  in  the  inner  one, 
next  to  the  nucleus.  I  should,  therefore,  be  disposed  to  take  the 
second  view,  namely,  that  there  is  no  relation  between  the  two 
strata  of  tubules,  but  that  there  was  a  first-formed  spherule  of  the 
smaller  ones,  and  finally  this  first  spherule  became  the  nucleus  for 
the  larger  Girvanella. 
Fig.  4,  a  and  />,  represents  a  form  of  Girvanella  of  a  rather  com¬ 
plex  structure.  The  tubules  average  *03  millim.  in  diameter,  and 
in  some  instances  have  the  appearance  of  branching ;  the  ramifica¬ 
tion,  if  such  there  be,  is  obscured  by  lines  which  traverse  one  or 
more  tubules  at  right  angles.  It  is,  however,  very  difficult  to 
believe  that  there  is  not  some  evidence  of  branching  in  this  speci¬ 
men,  and,  if  so,  the  discovery  is  a  decided  advance  in  our  efforts  to 
determine  the  true  nature  of  Girvanella. 
