Ribosomes  in  mitochondria  from  different  species  exhibit various
   sedimentation  coefficients,  different  from the cytoplasmic ribosome
   coefficient  of  80S  of  all  eukaryotes.  The  80S  coefficient  for
   Tetrahymena is probably coincidental.

   This   supports   the   endosymbiotic  hypothesis  of  the  origin  of
   mitochondria.