FRAGMENTATION

Fragmentation is only seen in multicellular organisms with a simple body organisation, On the other hand regeneration is observed in fully differentiated multicellular organisms. Another important point to remember is that Regeneration takes place with the help of certain specialized cells.

 

Renegeration is the growing back of a lost part of the body of an organism. It is also used as a method of defence. Fragmentation is the unintentional cutting up of the body of an organism which each grows into different organism.

Fragmentation is seen in multi-cellular organisms with relatively simple body organisation. Here the body of the organism simply breaks up into smaller pieces upon maturation. These pieces or fragments grow into new individuals. Eg- spirogyra.

Planaria can reproduce by both methods.

In planaria, fragmentation usually begins with a transverse constriction just behind the pharynx, which increases until the two parts separate and move away from each other. The head grows a new tail, and the tail grows a new head.

Planaria, can regenerate a whole body from a piece one-eighth the size of its original body.