The act or process of dividing into segments; specifically ( Biol.), a self- division into segments as a result of growth; cell cleavage; cell multiplication; endogenous cell formation.

A dividing into segments.

A dividing or splitting into segments.

Out of this agitation arises a little spot, that is usually round, and enlarges progressively to reach a maximum, after which it diminishes, with frequent segmentation and shrinkage. – Astronomy for Amateurs by Camille Flammarion

It expresses one of the prime characteristics of this class of animals, namely, that of segmentation. – Directions for Collecting and Preserving Insects by C. V. Riley

The segmentation is plainly visible. – The Glow-Worm and Other Beetles by Jean Henri Fabre