What has an immunological function and is not present in adults?

The thymus gland has an immunological function and is primarily active in children, playing a crucial role in the development of T-cells, which are essential for the immune response. As individuals reach adulthood, the thymus gradually shrinks and becomes less functional, leading to a decreased production of new T-cells. While remnants of thymic tissue may remain, the gland is not as prominent or active in adults as it is in children.