Fertilization occurs when sperm swim to an egg inside an archegonium.
Pregnancy begins with a fertilized egg.
Pregnancy begins after sperm swim to an egg inside an archegonium.
Sperm swim to an egg inside a what?

  - gastropod shells
  - aqueous solution
  - archetype
  - archive
  - ocean water
  - pollen
  - archegonium
  - sperm