In  accordance  with  the  results  of  the  most  recent
investigation,  and  in  connection  with  which  the  names  of  Greeff  and  Butschli
have  especially  to  be  mentioned,  it  has  been  demonstrated  beyond  question
that  in  its  more  complex  form  this  structure  is  enclosed  within  a  delicate
and  hyaline  bounding  membrane  or  pellicle,  which  may,  perhaps,  be  most
appropriately  compared,  physiologically  and  so  far  as  its  structureless
nature  is  concerned,  with  the  similarly  transparent  and  structureless  pellicle
ensheathing  the  constituent  elements  of  ordinary  muscular  tissue,  known
as  the  "  sarcolemma."  It  is  apparently  of  this  hyaline  supplemental
envelope  alone  that  the  slender  and  transparent  filamentous  cords,  or
funiculi,  are  composed  that  hold  in  union  with  one  another  the  otherwise
disjointed  fragments  of  the  compound  endoplast,  as  represented  in  the
genera  Loxodes  and  Loxophyllutn,

That  marked  disparity  of  aspect  and  significance  recorded  of  the  infu-
sorial endoplast,  as  compared  with  the  ordinary  histologic  nucleus,  is  found
to  extend  likewise  to  the  nucleolus  or  endoplastule. In  all  ordinary  tissue-
cells  this  special  structure  is  found  to  constitute  an  integral  and  essential
constituent  of  the  nucleus,  of  which  organ  it  presents  the  appearance
merely  of  a  central,  more  solid,  and  opaque  spheroidal  fragment  With  the
majority  of  the  Flagellata  and  some  few  Ciliata,  such  as  Pleuronema  and  its
allies,  and  many  of  the  Chilodontidae,  a  similar  contour  and  relationship


NUCLEOLUS  OR  EXDOPLASTULE. 77

with  the  associated  nucleus  or  endoplast  is  maintained  ;  but  among  the
greater  portion  of  the  representatives  of  this  last-named  group  an  altogether
different  plan  of  arrangement  is  found  to  obtain. The  nucleolus  or  endo-
plastule  is,  in  these,  no  longer  immersed  within  the  substance  of  the  nucleus  or
endoplasty  but  attached  to  its  external  periphery,  or,  it  may  be,  completely
isolated  from  it    Familiar  instances  of  such  simple  lateral  attachment  of  the
endoplastule  are  afforded  by  the  genera  Paranucium,  Balantidium^  and
Nyctottierus ;    this   phenomenon,   however,   attains   its   most   conspicuous
development  among  the  Oxytrichidae  and  other  Hypotricha,  in  which  the
endoplast,  as  before  stated,  is  usually  represented  in  duplicate,  and  each
independent  element  accompanied  by  a  sometimes  adherent  and  sometimes
detached,  minute,  oval  endoplastule. In  Stylonychia  mytilus,  mostly  pending
the  process  of  multiplication  by  binary  subdivision,  two  or  even  three  endo-
plastular  fragments  are  sometimes  found  associated  with  a  single  endoplastic
element. 