56 
formed  at  this  point/'  In  a  subsequent  paper  on  the  anatomy  of 
Diachaeta  this  opinion  is  also  maintained. 
The  worms,  collected  by  Prof.  Weber,  being  in  an  excellent  state 
of  preservation ,  I  resolved  to  examine  this  curious  spot  accurately  and 
to  see  if  there  really  exists  „a  zone  of  growth/'  as  suggested 
by  Fr.  Müller  and  Beddard. 
In  almost  all  our  examples  the  caudal  zone  (it  appears  prefe 
rable  to  me  to  make  use  of  such  an  indifferent  term,  which  prejudices 
nothing  about  the  morhological  value  of  this  body-region)  is  visible; 
as  stated  by  Fr.  Müller,  it  lies  always  on  a  definite  distance,  about 
130  segments  according  to  Perrier,  from  the  cephalic  extremity. 
If  therefore  really  a  formation  of  new  segments  takes  place  on  this 
spot,  it  can  only  be  the  cas,e  in  the  direction  of  the  caudal 
region. 
On  examining  the  body-wall  of  the  caudal  zone  on  a  glass-slide 
(fig.  38)  as  a  flat  preparation  in  glycerine,  we  see,  that  six  segments 
are  divided  by  a  circular  groove  in  two  rings,  which  have  each  half 
their  longitudinal  diameter.  This  division  is  not  equally  obvious  over 
the  whole  periphery  of  the  body,  because  the  grooves  in  the  vicinity 
of  the  ventral  median  line  grow  more  or  less  inconspicuous.  Lon- 
gitudinal sections  prove  also  (fig.  39),  that  these  grooves  are  most 
developed  at  the  dorsal  side,  though  even  here  they  are  sometimes 
nothing  but  a  shallow  depression  of  the  epidemis-layer;  in  the  ven- 
tral median  region  no  signs  of  grooves  are  visible. 
The  most  striking  feature  of  the  body- wall  in  the  caudal  zone,  is 
the  peculiar  distribution  of  the  bloodvessels;  instead  of 
the  net-work  of  fine  capillary  vessels,  which  occurs  in  other  segments, 
we  find  here  in  each  segment  two  bands  of  large  vessels  closely  crow- 
ded together,  each  of  them  corresponding  to  a  half  segment.  In  the 
ventral  median  region  however  this  vessels  are  hardly  discernible. 
Transversal  and  longitudinal  sections  (fig.  40)  learn  us,  that  those 
vessels  are  situated  in  the  highly  developed  layer  of  connective  tissue, 
found  between  the  layers  of  circular  and  longitudinal  muscles.  Though 
I  never  detected  bloodvessels  in  the  epidermis  itself,  as  stated  by 
Beddard,  the  red  colour  of  the  caudal  zone  during  life,  is  doubtless 
due  to  those  bands  of  densely  crowded  vessels,  and  the  suggestion 
arises  that  on  this  spot  an  active  respiration  takes  place  and  that 
perhaps  new  elements  are  formed. 
