In biology, a whorl is a cluster of cells or tissue that surrounds another and wraps around another in an expanding circular pattern. Whorls occur at the ends of different structures or in the middle of structures. Structures of some organs are often described as whorls and used in the aid of identification.
The Hassall's corpuscle, formed from type VI epithelial reticular cells in the thymus, is an example of a whorl-shaped structure.