Millions  of  living  beings  working  together  live  inside  of
this  moving  fort  we  call  the  turtle.
FIG.  22. — Skeleton  of  Turtle.     Glyptodon  clavipes.
What  difference  can  there  be  in  the  intelligence  or  skill
required  in  building  a  submarine  by  human  beings  and
the  building  of  a  fish  by  the  cells?  In  every  case  there
must  be  a  preconceived  plan,  a  purpose  to  capture  and
escape,  to  do  this  or  that.  They  are  made  with  an  end
and  purpose  in  view.  The  time  will  evidently  come  when
every  important  battle  will  be  fought  either  in  the  air  or
under  water.  The  submarine  now  must  have  eyes  in
order  to  see  where  to  go  and  so  as  not  to  run  into  nets.
Inside  are  the  individuals  who  run  it  and  take  care  of  it


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131


precisely  in  the  same  manner  that  the  cells  run  and  take
care  of  the  individual  they  inhabit,  be  it  animal  or  plant.
Think  of  that  invisible  crab !  How  are  the  cells  able  to
build  themselves  into  a  structure  so  as  to  be  transparent?
Those  are  secrets  for  us  to  solve.
FIG.  23. — A  submarine   made   by   the   cell.
