 Recently, advances in immunology have allowed the function of the thymus in T-cell maturation to be more fully understood.The thymus is present in all jawed vertebrates, where it undergoes the same shrinkage with age and plays the same immunological function as in other vertebrates.Recently, a discrete thymus-like lympho-epithelial structure, termed the "thymoid", was discovered in the gills of larval lampreys.