Abstract
The vitellogenin (yolk protein) of the monarch butterfly has been identified by electrophoretic and immunochemical techniques. In freshly emerged female adults ligature of the neck prevents appearance of this protein in the hemolymph; it prevents yolk deposition and egg maturation as well. These processes are restored by injection of juvenile hormone; the restoration involves induction of vitellogenin synthesis, as shown by incorporation of [3H]leucine.