MR.  R.  OWEN  ON  THE  ANATOMY  OF  LINGUATULA  T^NIOIDES.  329 
that  in  the  Slug  {Limax) ,  in  which  the  nerves  of  the  body  radiate  nearly  in  a  sym- 
metrical manner  from  a  single  suboesophageal  ganglion,  the  two  posterior  filaments 
being  the  longest,  and  extending  almost  parallel  to  each  other  to  the  posterior  extre- 
mity of  the  body.  It  may  also  be  observed,  that  the  disposition  of  the  muscular  system 
in  Limax  is  analogous  to  that  of  Ldnguatula,  being  most  developed  at  the  sides  of  the 
foot,  and  least  along  the  middle  line,  which  is  thin  and  semitransparent  when  viewed 
against  the  light.  If  one  might  be  permitted  to  trace  further  the  analogy  of  form  sub- 
sisting between  genera  so  widely  separated  in  other  important  particulars,  the  two 
fosscB,  with  their  little  hooks,  on  either  side  of  the  mouth  of  Linguatiila,  might  be  com- 
pared with  the  two  depressions  which,  when  the  tentacles  are  retracted,  appear  in  the 
same  situation  in  the  head  of  the  Slug.  It  is  the  superior  organization  of  these  parts 
which  renders  necessary  the  further  development  of  the  nervous  system  of  the  Slug  ; 
and  the  completion  of  the  cerebral  ring  and  the  development  of  the  supraoesophageal 
ganglion  constitute  the  chief  difference  subsisting  between  it  and  Linguatiila  in  this  part 
of  their  organization. 
The  superior  powers  of  locomotion  with  which  the  Slug  is  endowed  render  it  necessary 
that  it  should  have  organs  of  sense  sufficiently  developed  to  explore  and  take  cognisance 
of  the  various  circumstances  in  which  it  may  be  placed.  The  action  of  the  muscles 
occasions  waste,  and  demands  a  proportionate  supply  of  new  material  for  its  continu- 
ance :  hence  the  necessity  of  the  superaddition  of  a  vascular  system  for  the  carriage  of 
the  restorative  molecules,  of  a  more  complex  digestive  apparatus  for  their  supply,  and 
of  respiratory  and  secretory  organs  for  the  elimination  of  the  waste  parts  of  the 
body. 
In  Linguatula,  on  the  contrary,  the  sphere  of  action  being  limited  to  a  dark  cavity 
in  the  interior  of  another  animal's  body,  the  necessity  for  these  superadded  structures 
does  not  exist.  Its  food,  being  already  animalized,  requires  only  a  simple  canal  to  com- 
plete its  assimilation,  without  the  assistance  of  teeth  or  salivary  or  biliary  organs. 
Neither  heart  nor  vessels  are  perceptible,  and  it  is  probable  that  nutrition  is  eifected 
by  transudation  and  imbibition  ;  and  here  we  may  notice  the  admirable  arrangement  of 
the  oviduct  with  reference  to  the  reception  of  the  materials  for  the  full  development  of 
the  myriads  of  ova  which  it  contains. 
Living  in  a  cavity  to  which  external  air  has  access,  it  might  be  expected  that  the 
vital  phenomena  of  Linguatula  would  be  more  energetic  than  in  other  Entozoa.  With 
respect  to  its  muscular  actions,  Rudolphi  observes  :  "  Motus  peculiares,  vermium  tere- 
tium  tamen  agitationibus  maxime  accedunt,  partem  nimirum  tam  anticam  quam  posti- 
cam  continuo  vel  retlectit  vel  inflectit,  minore  tamen,  quam  illi,  corporis  vi  utitur, 
neque  cutis  musculorum  apparatum  notabilem  continet.  A  Trematodum,  vel  Distoma- 
tum.,  vel  Amphistomatum  et  Monostomatum,  vel  etiam  Polystomatis  uncinulati,  moti- 
bus  quam  maxime  recedit,  neque  cum  Tseniis  ullo  modo  comparari  potest 
'  Hist.  Ent.,  torn.  ii.  p.  443. 
