Of  the  dissemination  of  Infusoria  in  time,  or  in  other  words  their  geolo-
gical distribution,  there  is,  as  a  necessary  consequence  of  their  mostly  soft
and  perishable  nature,  scarcely  a  trace  preserved.  The  hard  coverings  or
loricae  of  a  few  species  have,  however,  been  recognized  by  Ehrenberg  in
the  Cretaceous  deposits,  and  referred  by  him  to  the  genera  Chatotyphla  and
Ceratium.  The  siliceous  loricae  of  the  Peritrichous  genus  Dictyocysta  occur
also  in  company  with  the  pelagic  Polycistina  of  the  Tertiary  formations,
and  there  can  be  but  little  doubt  that  the  Infusoria  in  their  simplest
condition  represent  one,  if  not  the  most  ancient,  of  the  stock-forms  of  the
Clonic  series.  Accepting,  in  fact,  the  Spongida  as  representatives  of
the  Choano-Flagellata,  a  subject-matter  which  is  fully  discussed  in  a  suc-
ceeding chapter,  the  Flagellate  section  of  the  infusorial  series  is  distinctly
traceable  through  every  marine  deposit  from  the  present  day  back  to  the
Cambrian  and  even  the  Laurentian  section  of  the  Palaeozoic  epoch.
PRESER  VA  TION.  1 1 3


Preservation  of  Infusoria.
