NEUROSECRETION 135 



tissues without the implication of other mechanisms. But in 

 annelids there are indications that a neurosecretory process is 

 involved as well. 



Harms (1948) found that the cerebral ganghon has a humoral 

 effect and that the anterior nervous system is essential to the process 

 of regeneration, suggesting that this is due to the necessary neuro- 

 secretory cells being limited to this region. 



Hubl (1956) removed the cerebral ganghon and the posterior 

 extremity of the animal at the same moment, observing that the 

 rear end will not grow again, thus confirming Harms's suggestion 

 that the anterior nervous system is essential for regeneration. This 

 action is an inhibitory one. Regeneration can occur if a short 

 period elapses between the operations. In 1953 Hubl showed that 

 the ^-cells of the cerebral ganglia are involved in regeneration and 

 in 1956 he considers that they are inhibitory to the process of 

 regeneration, as also are cells in the central segmental ganglia. 

 When ^-cells are removed a short time after the hind end is 

 removed the inhibition is released and growth can take place. 

 Excision of parts of the nervous system further to the rear e.g. the 

 sub-oesophageal ganglion and the adjoining ventral nerve cord, 

 also inhibits new growth, whilst loss of the ventral nerve chain 

 from body segments has a lesser inhibitory effect. 



The secretory cells of the nervous system have complementary 

 effects upon one another. The cells of the sub-oesophageal ganglion 

 affect the 6-cells of the cerebral ganghon. The cells of the ventral 

 nerve cord show a gradient of activity, being more productive 

 anteriorly than posteriorly. The w-cells contained in the sub- 

 oesophageal ganglion seem to be causal agents in promoting 

 regeneration, and removal of this ganglion inhibits gro\\1;h since the 

 appropriate cells are no longer present. This is in contra-distinc- 

 tion to the effect of the Z>-cells which are inhibitory when present 

 and allow growth to occur when they are removed. 



In cases where the posterior end of the body is removed without 

 disturbing the anterior end some other stimulatory mechanism 

 must invoke activity of the w-cells (sub-oesophageal ganglion) in 

 order that regeneration can occur, perhaps removal of the c-cells 

 of the ventral ganglia at the rear upsets the normal hormonal 

 balance between the various gangha, and thus induces secretion in 

 the anterior ganglia. As regeneration proceeds more t-cells are 



