Possible Clues:

• Melatonin-secreting gland
• With sharp implement, not hard to cure this gland
• Coney, perhaps, in the ring of a bell
• Before a half century a tree might long to be in the brain
• Long line encompassing a description of a gland
• Long to join a student organ
• Description of gland -- long? Entirely lacking length
• Al is like a cone on the brain
• Bit of a thinker devising a ploy in bed
• Penny and the alien moved like a 28-across