Civil Code (Cap. 16), article 759

759. Where the usufruct o f a thing is left to one person, and the ownership of the same thing to another person, under the condit ion that the latter be still alive at the time of the cesser of the usufruct, it shall be lawful to substitute a third person in the place of the person in whose favour the ownership is devised in the event of such condition not being fulfilled. Disposition under condition that cannot be fulfilled before death of heir or legatee.