0

Identical vs fraternal twins.

2

Information on the importance and functions of the placenta.

14

I was never good at arithmetic, but my family firmly believed that they could instill the basic principles of math in my silly, liberal arts head. The process left several indelible memories. This is one of them.

32

This is how the sperm meets an egg until it is fertilized as a healthy fetus in the mother’s womb.