53 
Perichaeta.  In  my  opinion  however,  the  supposed  homology  is  not 
well  founded,  as  the  epidermis-organs  of  Pontoscolex  do  not  show 
much  resemblance  neither  in  their  situation,  nor  in  their  appearance 
with  the  bristle-cells  of  Anachaeta  ;  the  latter  ones  are  large ,  glandular 
cells,  which  are  not  entirely  embedded  in  the  epidermis,  but  extend 
themselves  at  a  distance  into  the  body-cavity.  Moreover  it  is  clear ,  that 
a  body  lying  in  the  circle  of  the  setae  ?  may  not  only  for  this  reason  be  con- 
sidered to  be  homologue  with  them.  Beddard  at  first  describing  the 
epidermal  structures,  found  in  Eudrilus ,  considered  them  as  representing 
rudimentary  setae,  afterwards  however  reexamining  them  in  Hyperiodri- 
lus  and  Heliodrilus  l)  he  came  to  the  opinion ,  that  they  must  rather  be 
regarded  as  of  a  sensory  nature ,  which  view  nearly  at  the  same  time  was 
put  forward  bv  myself  with  regard  to  those  bodies  in  Eudrilus 2).  The 
sensory  bodies  of  Lumbricus,  according  to  the  investigations  of  Cerfon- 
taine  3),  are  also  in  many  segments  specially  to  be  found  in  the  ele- 
vated zone  of  the  bristles ,  so  being ,  in  his  opinion ,  far  better  situated 
for  their  sensory  function.  I  observed  that  in  much  contracted  spe- 
cimens of  Pontoscolex,  the  bristle-zone  of  the  anterior  segments 
also  has  the  appearance  of  an  elevated  ridge.  Though  the  finer  structure 
of  the  epidermis-bodies  of  Pontoscolex  is  not  sufficiently  known,  it 
seems  to  me  more  probable ,  that  they  too  are  of  a  sensory  nature. 
The  different  authors,  who  examined  P.  corethrurus,  are  not  quite 
in  agreement  about  the  structure  of  the  cephalic  extremity  of  this 
worm.  Fritz  Müller  4)  says ,  that  if  the  worm  protudes  the  cephalic 
extremity,  from  out  the  first  segment  one  or  two  other  segments 
come  in  sight,  besides  a  long-stalked,  club-shaped  cephalic  lobe. 
Perrier  on  the  contrary  states  ,  that  the  cephalic  lobe  is  totally  absent, 
that  the  mouth  is  terminal  and  surrounded  by  the  buccal  segment, 
which  is  devoid  of  bristles;  but  that  in  front  of  this,  another  segment 
without  bristles  exists,  and  that  both  can  be  inverted.  Rosa  rightly 
pointed  out,  that  if  Perrier's  view  were  right,  all  organs  in  Pontos- 
colex would  lie  one  segment  more  backward  than  in  other  Lumbrici- 
dae;  but  as  this  suggestion  is  not  very  probable,  he  believes  the 
segment,  which  Perrier  calls  the  first,  to  be  the  everted  portion  of 
1)  Quartl.  Journ.  Micros®.  Science,  Yol.  XXXII,  1891,  p.  235. 
2)  Mém.  Soc.  Zool.  de  France,  Vol.  Ill,  1890,  p.  1,  pl.  VIII. 
3)  Archives  de  Biologie,  T.  X,  1890,  p.  363. 
4)  Archiv,  f.  Naturgeschichte,  Jhrg.  XXIII,  1857.  p.  113. 
