10 
DR.  R.  E.  GRANT  ON  THE  NERVOUS  SYSTEM  OF  BEROi^  PILEUS, 
tapering  to  a  very  fine  extremity.  Along  their  whole  course  they  present  minute  equi- 
distant filaments,  extending  from  their  lower  margin,  which  coil  themselves  up  in  a  spiral 
manner,  and  adhere  close  to  the  tentacula  when  they  are  about  to  be  withdrawn  into 
their  sheaths  or  tubes.  These  tubes  have  a  sigmoid  form,  and  are  shut  and  somewhat 
dilated  at  their  upper  extremity.  The  tentacula  seem  to  be  spirally  twisted  in  them  when 
withdrawn.  The  tentacula  are  often  thrown  out  from  the  tubes  to  their  full  extent  by 
one  impulse,  and  the  slow  uncoiling  of  the  slender  serpentine  filaments  from  their  margin 
is  then  very  beautiful ;  when  coiled  up,  they  appeared  like  very  minute  tubercles  along 
the  side  of  the  tentaculum.  The  animal  often  poised  its  body  in  the  water,  without 
moving  the  cilia,  by  extending  these  minute  filaments  to  the  bottom  of  the  vessel.  I 
observed  that  both  the  Beroe  and  the  Equorea  were  inconvenienced  by  each  other's 
presence,  and  less  free  in  the  extension  of  their  delicate  tentacula,  until  they  were  put 
into  separate  vessels. 
At  a  short  distance  above  the  mouth  I  could  perceive  a  double  transverse  filament  of 
a  milky  white  colour,  like  that  of  the  abdominal  nerves  of  the  Pectinaria  and  other 
transpareat  animals,  which  formed  a  continuous  circle  round  the  body.  In  the  middle 
of  the  space,  however,  between  each  of  the  bands  of  cilia,  these  cords  presented  a  small 
knot  or  ganglion,  so  that  there  were  eight  ganglia  in  the  course  of  this  ring.  From  each 
of  these  ganglia  two  nerves  on  each  side  passed  to  the  adjoining  band,  and  a  larger 
filament  from  each  ganglion  could  be  traced  upwards  in  the  middle  of  the  transparent 
space  between  the  bands  to  beyond  the  middle  of  the  body.  In  the  course  of  these 
longitudinal  middle  filaments  two  or  three  smaller  ganglia  could  be  observed,  from 
which  filaments  were  directed  inwards  to  the  viscera.  These  filaments  and  ganglia  were 
situated  near  the  surface  of  the  body  ;  and  from  their  general  appearance  and  their  mode 
of  distribution,  there  can  be  little  doubt  that  they  constitute  the  nervous  system  of  this 
animal.  This  arrangement  of  the  nervous  system  is  analogous  to  that  of  Holothuria 
and  Asterias  among  the  Echinoderma,  in  the  circular  disposition  of  the  central  filaments 
and  ganglia,  and  in  the  regular  radiation  of  nerves  from  that  circle.  All  the  movements 
of  the  Beroe  are  of  a  lively  character  ;  its  tentacula  and  the  lips  of  the  mouth  appear  to 
be  exquisitely  sensible  ;  the  animal  frequently  contracts  its  body  longitudinally  or  trans- 
versely by  a  sudden  impulse,  and  when  it  is  at  rest  the  slightest  agitation  of  the  vessel 
containing  it,  causes  it  to  commence  instantaneously  the  rapid  vibration  of  its  cilia. 
The  Rotiferous  animalcules  are  found  to  possess  a  complex  nervous  system,  consisting 
of  cerebral  and  oesophageal  ganglia  and  longitudinal  nervous  filaments,  and  even  the 
Polygastric  animalcules  possess  organs  of  vision.  I  am  inclined  therefore  to  believe, 
that  although  nerves  have  not  hitherto  been  shown  in  the  Acalepha,  they  will  be  found 
even  in  the  simpler  forms  of  Medusa,  which  I  have  shown  elsewhere  to  be  affected  by 
light,  as  well  as  Actiniae,  Hydra,  and  Furcocercce. 
The  cilia  of  this  Beroe  are  the  largest  I  have  yet  met  with  in  any  animal.  These 
singular  minute  vibratile  organs  perform  important  functions  in  the  simpler  forms  of 
