Worms are made up of over a hundred segments, each species of worm having a different number, e.g the common earthworm Lumbricus terrestris has up to 160 segments, whereas the composting worm Eisenia fetida has only up to 110 segments.
The number of segments and the location of the worms organs in the segments is the main way scientists can tell the species apart.
Can worms grow back a missing part?
Worms can regenerate lost parts of their bodies, but only if very few segments are cut off, so cutting a worm in two will not make 2 worms grow back. If the cut is near the head, then the decapitated head will die and a new one will grow back. If the cut is nearer the tail, then the cut off tail will die and a new one will grow. Sometimes the worm will get confused and a tail will grow another tail, or a head will grow another head!
Worm transplants are also possible - scientists have sewn the head of a worm to the tail of another of the same species. The two parts have become fused within 2 weeks, even if they were sewed up at 90° angle probably by the same mean scientists who tried taking their brains out!