To children below the age of puberty and in the power of the testator, not only can such a substitute as we have described be appointed, that is, one who shall take on their failing to inherit, but also one who shall be their heir if, after inheriting, they die within the age of puberty; and this may be done in the following terms, 'Be my son Titius my heir; and if he does not become my heir, or, after becoming my heir, die before becoming his own master (that is, before reaching puberty), then be Seius my heir.' In which case, if the son fails to inherit, the substitute is the heir of the testator; but if the son, after inheriting, dies within the age of puberty, he is the heir of the son. For it is a rule of customary law, that when our children are too young to make wills for themselves, their parents may make them for them. 1 The reason of this rule has induced us to assert in our Code a constitution, providing that if a testator has children, grandchildren, or greatgrandchildren who are lunatics or idiots, he may, after the analogy of pupillary substitution, substitute certain definite persons to them, whatever their sex or the nearness of their relationship to him, and even though they have reached the age of puberty; provided always that on their recovering their faculties such substitution shall at once become void, exactly as pupillary substitution proper ceases to have any operation after the pupil has reached puberty. 2 Thus, in pupillary substitution effected in the form described, there are, so to speak, two wills, the father's and the son's, just as if the son had personally instituted an heir to himself; or rather, there is one will dealing with two distinct matters, that is, with two distinct inheritances. 3 If a testator be apprehensive that, after his own death, his son, while still a pupil, may be exposed to the danger of foul play, because another person is openly substituted to him, he ought to make the ordinary substitution openly, and in the earlier part of the testament, and write the other substitution, wherein a man is named heir on the succession and death of the pupil, separately on the lower part of the will; and this lower part he should tie with a separate cord and fasten with a separate seal, and direct in the earlier part of the will that it shall not be opened in the lifetime of the son before he attains the age of puberty. Of course a substitution to a son under the age of puberty is none the less valid because it is a integral part of the very will in which the testator has instituted him his heir, though such an open substitution may expose the pupil to the danger of foul play.