MR.  R.  OWEN'S  REMARKS  ON  THE  ENTOZOA. 
393 
Having  been  thus  led,  in  considering  the  place  which  Trichina  ought  to  occupy  in 
the  natural  system,  to  review  the  arrangements  of  the  Entozoa  generally,  to  trace  their 
affinities  to  the  other  classes  of  Radiata,  and  thus  to  take  into  consideration  the  grounds 
for  retaining  or  otherwise  that  division  of  the  Animal  Kingdom,  I  now  proceed  to  consi- 
der the  Entozoa  which  are  separated  from  the  Sterelmintha,  and  examine  them  in  relation 
to  the  classes  of  the  Radiata  which  remain  after  the  dismemberment  of  the  Acrita. 
The  Vers  Cavitaires  of  Cuvier,  which  include  the  Nematoidea  of  Rudolphi  and  the 
Vers  Rigidules  of  Lamarck,  together  with  the  genus  Nemertes,  and  the  genus  Linguatula 
{Pentastoma,  Rud.)  previously  described,  I  propose  to  separate  into  two  classes  ;  the 
one  including,  with  the  Nematoidea,  the  genera  Linguatula  and  Sipunculus,  under  the 
term  Coelelmintha^  ;  the  other  formed  by  the  Vers  Rigidules  under  the  term  Epizoa,  which 
the  researches  of  Dr.  Nordmann  have  recently  shown  to  exhibit  a  much  higher  type  in 
their  free  moving  condition  than  many  of  them  afterwards  exhibit  when  they  have 
become  fixed  to  the  animals  which  they  infest. 
Both  these  classes  have  a  condition  of  the  nervous  system  in  common  with  the  Echi- 
nodermata  and  Rotifer  a  of  Professor  Ehrenberg,  which  may  be  termed  the  filamentous, 
since,  in  all  these  animals,  simple  ungangliated  nervous  filaments  can  be  traced,  extend- 
ing from  a  point  near  the  commencement  of  the  alimentary  canal ,  in  number  and  direc- 
tion corresponding  with  the  form  of  the  body.  This  condition  of  the  nervous  system  is 
accompanied  by  a  distinct  development  of  the  muscular  system,  and  especially  of  a 
muscular  tunic  of  the  alimentary  canal,  which  now  floats  in  an  abdominal  cavity,  and, 
with  the  exception  of  one  family  of  Echinodermata,  has  a  distinct  anus.  There  is  no  longer 
in  this  division  any  instance  of  fissiparous  or  gemmiparous  reproduction.  In  the  Echino- 
dermata, which  are  allied  to  the  Polypi  vaginati  by  the  fixed  pedicellate  Encrinites,  the 
nutritious  fluid  circulates  in  distinct  arteries  and  veins  ;  and  in  the  Holothurits,  express 
respiratory  organs  are  superadded.  From  the  Echinodermata  which  present  this  length- 
ened worm-like  form,  together  with  the  softening  down  of  the  external  crust,  the  Sipun- 
culi  make  an  easy  and  natural  transition  to  the  Ccelelmintha,  to  which  class,  from  the 
absence  of  respiratory  organs  and  tubular  feet,  from  the  obscure  traces  of  a  vascular 
system,  and  the  disposition  of  the  nervous  filaments,  they  appear  to  me  to  have  closer 
affinities  than  the  Echinodermata. 
The  Ccelelmintha,  thus  constituted,  present  the  same  varieties  in  the  condition  of  the 
generative  system  as  the  Sterelmintha.  We  find  the  simple  female  apparatus  without 
male  organs,  or  the  cryptandrous  type,  in  the  SipuncuU ;  the  superadded  male  glands, 
but  without  reciprocal  fecundation,  in  the  Linguatula ;  and  the  separate  sexes  in  the 
Nematoidea, 
If  we  distribute  the  internal  parasites  of  the  human  body  according  to  the  preceding 
attempt  at  a  natural  arrangement  of  the  Entozoa,  they  will  be  found  to  belong  to  at 
least  three  distinct  classes  of  animals. 
'  KoiXos,  cavus,  eXim^s,  lumhricus. 
