Final answer:
The fine, colorless hair that covers the fetus around the sixth month of pregnancy is called lanugo. It helps to protect and keep the fetus warm in utero. Along with the hairs of lanugo, a waxy substance known as vernix caseosa also forms to protect the fetus's skin.
Step-by-step explanation:
Around the sixth month of pregnancy, the developing fetus is covered by a fine, colorless hair called lanugo. This hair begins to grow on the face and will eventually cover most of the body, protecting the fetus and keeping it warm. Lanugo is typically shed close to the time of birth, although it can be present on extremely premature infants. Another key development during this stage is the formation of a waxy coating called vernix caseosa, which protects the fetal skin from amniotic fluid and provides lubrication during childbirth.
Both lanugo and vernix caseosa play crucial roles in fetal development, helping the fetus to stay warm and protected within the womb. Through the stages of pregnancy, as the fetus grows and develops, these features serve as adaptations to the fetal environment and are eventually shed as the fetus prepares for birth.