33 
is  specially  obvious  in  the  segments,  containing  the  male  genital 
organs,  while  it  is  no  more  recognisable  in  the  anterior  body-region. 
The  longitudinal  muscle-fascicle ,  in  the  median  dorsal  area  of  each 
segment ,  considered  by  Ude  l)  as  the  opening-muscle  of  the  dorsal 
pore,  could  be  distinguished  very  clearly.  I  do  not  understand  that 
Cerfontaine,  who  lately  admirably  worked  out  the  histological  struc- 
ture of  the  body-wall  of  Lumbricus,  makes  no  remark  upon  those 
fascicle  2). 
The  nephridia  consist  of  a  net- work  of  delicate  tubules,  spread 
over  the  whole  internal  side  of  the  body- wall,  except  on  a  narrow 
median  area  at  the  ventral-  and  dorsal  side.  However  there  is  some 
difference  in  their  arrangement  in  the  anterior  and  the  posterior  seg- 
ments of  the  body;  for  in  the  anterior  body-region  they  line  the 
whole  inner  surface  of  the  body-wall ,  whereas  in  the  segments  behind 
the  clitellum  they  are  confined  to  four  groups  on  each  side.  The  three 
external  groups,  having  a  roundish  shape,  are  situated  enternally  to 
the  dorsal  series  of  bristles;  the  fourth  internal  group,  of  a  more 
oblong  shape,  is  for  the  greater  part  confined  between  the  ventral 
and  dorsal  series  of  bristles. 
The  dorsal  vessel  is  a  single  tube,  which  communicates  with  the 
ventral  trunc  through  five  pairs  of  commissural  vessels,  of  which  the 
posterior  three  are  the  largest. 
The  pharynx  is  covered  by  a  compact  mass  of  glands,  dividing 
posteriorly  in  two  symmetrical  halfs,  The  gizzard  lies  in  segment  VI 
and  VII  and  consists  of  two  divisions;  its  muscular  wall  being  in- 
terrupted by  a  narrow  membranaceous  interval. 
In  segment  XV,  XVI  and  XVII  the  tubular  intestine  is  provided 
on  each  side  with  calciferous  glands. 
There  are  two  pairs  of  spermathecaein  segments  VIII  and  IX; 
each  of  them  consists  of  a  tubular  pouch,  which  is  slightly  curved 
and  terminates  in  an  enlarged  extremity  (Pl.  II.  fig.  4).  Below  its 
middle  the  spermatheca  is  furnished  with  a  pyriform  diverticulum,  that 
is  filled  with  spermatozoa. 
As  already  pointed  out  by  different  authors,  there  exists  some  diffe- 
rence in  the  minute  structure  of  the  different  parts  of  the  sperma- 
1)  Zeitschrift  f.  wissens.  Zoologie,  Bd.  XLIII,  1886,  p.  87,  pl.  IV. 
2)  Archives  de  Biologie,  T.  X,  1890,  p.  327,  pl.  XI— XIV. 
3 
