The  retraction  of  the  pseudopodic  processes  of  the  Rhizo-Flagellata,  with
the  retention  of  the  flagellum  and  capacity  to  incept  food  at  any  point
of  the  periphery,  is  alone  required  to  perfect  the  passage  to  the  next
succeeding  order,  that  of  Flagellata-Pantostomata.  In  this  group  we  find
a  considerable  diversity  in  the  number  and  character  of  the  flagellate
appendages,  this  organ  being  single  in  such  simple  types  as  Monas  and
Bodo^  double  in  Spumella  dsid  Anihophysa,  while  in  others  such  as  Tetramitus,
Hexamita^  and  Lophomonas,  the  number  is  very  considerably  increased  It
is  among  the  Polymastigous  section  of  this  order,  somewhere  near  Lopha-
ntonaSy  that  the  remarkable  compound  marine  type  Magosptuzra  planulUy
PI.  I.  Figs.  12-17,  upon  which  Professor  Haeckel  has  proposed  to  found  a
new  class  group  entitled  the  Catallacta,  should  apparently  be  placed.  A
special  feature  of  Magosphcsra^  as  described  by  Haeckel,  is  exhibited  by
its  tendency  to  revert  to  a  repent  amoeboid  phase  pending  the  process
of  encystment  and  reproduction.  A  similar  disposition  is,  however,  as
hereafter  shown,  shared  by  the  majority  of  the  Pantostomata.
