A type of skin gland which is well developed and functional in females, but non-functional and vestigial in the male is:
mammary gland
Mammary gland, milk-producing gland characteristic of all female mammals and present in a rudimentary and generally nonfunctional or vestigial form in males. Mammary glands are regulated by the endocrine system and become functional in response to the hormonal changes associated with parturition.