390 
MR.  R.  OWEN'S  REMARKS  ON  THE  ENTOZOA. 
effected  by  reciprocal  intromission.  Again,  distinct  sexes  are  attributed  to  the  Echino- 
rhynchi,  the  highest  organized  of  the  Parenchymatous  Intestinal  Worms. 
Thus  the  generative  system  fails  to  afford  a  character  applicable  to  the  whole  of  the 
Acrita  of  Mr.  MacLeay ;  and  we  are  equally  unable  to  predicate  of  them  a  simple  diges- 
tive sac  without  an  anal  outlet.  In  general  it  may  be  observed,  that  it  is  only  with 
respect  to  the  nervous  system  that  we  can  attribute  a  community  of  structure  to  a  pri- 
mary division  of  the  animal  kingdom. 
Now  the  classes  which  present  the  diffused  condition  of  the  nervous  globules,  are  the 
Polygastrica,  Spongia,  Polypi,  and  Acalephcs ;  to  which  must  be  added  the  Vers  Intesti- 
naux  Parenchymateux  of  Cuvier,  or  Vers  MoUasses  of  Lamarck,  and  of  which  I  would 
propose  to  form  a  class  of  Acrita  under  the  term  Sterelmintha^ . 
But  as  all  the  classes  of  the  Acrite  division  exhibit  the  lowest  stages  of  animal  orga- 
nization, and  are  analogous  to  the  earliest  conditions  of  the  higher  classes,  during  which 
the  changes  of  the  ovum  or  embryo  succeed  each  other  with  the  greatest  rapidity,  so  we 
find  that  the  species  in  each  class  successively  present  modifications  of  their  pecuhar 
types,  which  come  into  close  approximation,  not  with  the  Acrite  classes  immediately 
succeeding  them,  but  with  some  one  or  other  of  the  classes  of  higher  groups  in  the 
animal  kingdom,  of  the  typical  form  of  which  the  Acrite  classes  represent,  as  it  were, 
the  germs.  Owing,  therefore,  to  this  tendency  to  ascend  in  the  Acrita,  it  becomes  pro- 
portionally more  difficult  to  assign  a  general  organic  character  to  that  than  to  any  of 
the  higher  divisions.  Even  with  respect  to  the  nervous  system  we  find,  as  we  are  led 
step  by  step  from  the  Hydra  to  the  Actinia  in  the  class  Polypi,  that  the  nervous  glo- 
bules begin  to  manifest  the  filamentous  arrangement  about  the  oral  orifice  of  the  last- 
named  genus  ;  that  in  passing  through  the  Sterelmintha  from  the  Hydatid  to  the  Echi- 
norhynchus,  we  come  also  to  perceive  traces  of  longitudinal  nervous  chords  in  that 
highly  organized  Entozoon  ;  and  that  in  the  Acalephcs,  examples  of  the  aggregate  form 
of  the  nervous  system  have  been  described.  But  even  supposing  these  exceptions  to 
be  well  founded,  and  the  filaments  to  be  really  nervous  which  have  been  so  considered^, 
yet  the  proportion  of  each  class  in  which  the  molecular  diffused  condition  of  the  nervous 
'  Srepeos,  solidus,  eXyutvs,  a  term  applied  by  the  ancients  to  intestinal  worms,  which  were  distinguished  into 
eXfiivdes  arpoyyvXai,  or  Intestinalia  teretia,  and  eXfxivdes  -rrXaTeiai,  or  Intestinalia  lata.  My  compound  is 
further  sanctioned  by  a  term  invented  by  Zeder  for  the  Entozoa  generally,  viz.  Splanchnelmintha,  which  term 
is,  however,  with  that  of  Entozoa,  equally  subject  to  the  objection  of  being  applied  to  animals  of  different  classes 
according  to  structure. 
-  Professor  Ehrenberg  has  recently  ascribed  to  the  Medusa  aurita  distinct  visual  organs,  in  the  form  of  minute 
red  points,  situated  on  the  surface  of  the  eight  brown-coloured  masses  set  round  the  circumference  of  the  disc. 
These  masses  consist  each  of  a  yellowish,  oval  or  cylindrical,  Uttle  body,  which  is  attached  to  a  small  and  deli- 
cate pedicle.  This  short  pedicle  arises  from  a  vesicle,  in  which  there  is  placed  a  glandular  body,  unattached, 
presenting  a  yellow  colour  when  viewed  with  transmitted  light,  and  a  white  colour  when  under  reflected  light. 
It  is  on  the  dorsal  aspect  of  the  yellow  head  which  surmounts  the  pedicle  that  the  well-defined  red  spot  is  seen 
which  Professor  Ehrenberg  considers  as  an  eye.  He  compares  the  eyes  of  Medusa  to  those  of  Rotifera  and 
Entomostraca.    The  glandular  body  situated  at  the  base  of  the  pedicle,  he  regards  as  one  optic  ganglion,  which 
