The principal female reproductive organs are those directly engaged in procreation, responsible for gamete production and reproductive support.
Step 1: Evaluation of choices.
- Mammary glands (Option 1): Mammary glands facilitate milk production and lactation; however, they are not primary sex organs.
- Uterus (Option 2): The uterus is vital for fetal development but does not produce eggs, the primary reproductive cell.
- Ovaries (Option 3): The ovaries are the principal female sex organs. They are responsible for egg (ovum) production and the secretion of reproductive hormones such as estrogen and progesterone.
- Cervix (Option 4): The cervix is a component of the female reproductive tract, but not a primary reproductive organ.
Step 2: Determination.
The primary female sex organ is the ovaries.
Final Answer: \[\boxed{\text{The correct answer is (3) Ovaries.}}\]