Cut upon Regeneration in Gunda ulvae. 



361 



After a longitudinal bisection the brain will easily regenerate the removed 

 naif, and the circuit of the nervous system is restored, often before the long 

 wound has healed over. Transverse sections across the ganglia, however, 

 are not followed by regeneration of the ganglia if more than about one-third 

 of the brain is taken away. The nervous system forms a complete ring, and 

 in every ease, where this ring is broken, regeneration of the nerve cords takes 

 place sufficiently to restore the circuit, though the cerebral ganglia may or 

 may not be regenerated. 



Text-fig. V shows an animal (text-fig. Ill, 3) where the cut passed across 

 the front of the ganglia, which were subsequently completely restored. Text- 

 Fig. VIII (text-fig. II T, 6) shows an animal in which the cut removed both 

 ganglia. In such conditions the nerve cords grow forward and fuse, but no 

 ganglia are regenerated, and the animals remain headless. Text-figs. VI and 

 VII show two worms (text-fig. Ill, 4 and 5 respectively) where the cut has 

 damaged both ganglia and where there is correspondingly defective restoration 

 of the head. 



Fig. V. — Horizontal Longitudinal Section through Complete Regenerated Head, 41 days 

 (text-fig. Ill, 3). ga., ganglion ; n.c, nerve cord ; op.n., optic nerve. 



