Final answer:
The mesencephalon does not mature into a secondary vesicle; the statement is false.
Step-by-step explanation:
The statement is false.
The midbrain, also known as the mesencephalon, does not mature into any secondary vesicle. It is already an established region of the brain at the primary vesicle stage of development and remains unchanged as the rest of the brain develops around it.
The primary vesicles (prosencephalon, mesencephalon, and rhombencephalon) further differentiate into five secondary vesicles (telencephalon, diencephalon, mesencephalon, metencephalon, and myelencephalon) that establish the major regions of the adult nervous system.