REGENERATION IN ANNELID NERVE CORD 169 
ferentiated cells scattered through these layers, but since the 
plug cells are mesodermal in origin, as I shall show later, and are 
capable of changing shape under the influence of a steady pull 
exerted along one axis, it seems probable that these plug cells 
might also develop contractile fibrils and fill the gap caused by 
the cut. More work is needed to determine whether this latter 
step actually takes place or not. The early stages of plug for- 
mation and cell elongation and orientation in response to muscle 
pull, are clearly shown in many of my slides. 
The digestive tract lies as a smaller tube within the cylin- 
drical body wall. As a rule, it is not cut during an operation 
and does not enter into very close relationship with the plug 
cells. Occasionally small fragments of chlorogogue cells may be 
distinguished, by their granular nature, in the plug, but their 
position here is accidental rather than purposeful. 
Between the digestive tube and body wall lie two other struc- 
tures, the nerve cord and blood-vessels (fig. 1, N. C. and Sub.). 
When the nerve is first cut the elasticity of its substance causes 
the ends to draw as far apart as the mesenteries will permit, 
sometimes even slipping through the sleeve in the septum into 
the next segment (fig. 3). This causes the mesenteries to assume 
a slanting position. In addition to the small vessels of the skin 
and muscles, the subneural vessel is cut and there may even be 
breaks in the ventral vessel. This allows blood to escape into 
the segment where the cut is. Experiments have been made 
with this blood to determine the part which it may play in the 
regeneration process. When a cut is made in the body wall, 
very little bleeding occurs, except from the large vessels. The 
small vessels are apparently closed by the first drop of blood 
which comes from the cut end. The closure of even the largest 
vessels, dorsal and ventral longitudinal vessels, is very rapid. 
We may say, then, that very little bleeding occurs when an 
earthworm is cut. 
If the ventral vessel be raised and a clean smooth capillary 
pipette inserted, a large amount of blood may be drawn without 
any closure of the cut. If this is run out under a cover-glass on 
a clean slide, the cover being slightly raised by a paraffin V open 
