Complex sentence: Though many of the traditions within the society are secret, the membership of each chapter is public, which differentiates Mortar Board from many of the secret societies that were formed in the late 19th century.
Split into simpler sentences: Though many of the traditions within the society are secret, the membership of each chapter is public. This differentiates Mortar Board from many of the secret societies that were formed at the same time in the late 19th century.