Planaria exhibits asexual mode of reproduction by regeneration process. It can regenerate in whatever plane it is cut. But the only condition is that the cut piece of the organism should have atleast 20 % of  neoblasts, the adult stem cells.

If a transverse cut is given, the cut parts develop into two different individuals.
If the longitudinal cut is given from the head to tip and just it is held ( not cut at the tail region), planaria develops two heads and can survive. Regeneration is also called as morphallaxis

Regeneration is different from reproduction as it does not involve any sex cells or vegetative propagules to give rise to new individual.