4 Not only when we leave our inheritance to children under the age of puberty can we make such a substitution, that if they accept the inheritance, and then die under that age, the substitute is their heir, but we can do it when we disinherit them, so that whatever the pupil acquires by way of inheritance, legacy or gift from his relatives or friends, will pass to the substitute. What has been said of substitution to children below the age of puberty, whether instituted or disinherited, is true also of substitution to afterborn children. 5 In no case, however, may a man make a will for his children unless he makes one also for himself; for the will of the pupil is but a complementary part of the father's own testament; accordingly, if the latter is void, the former will be void also. 6 Substitution may be made either to each child separately, or only to such one of them as shall last die under the age of puberty. The first is the proper plan, if the testator's intention is that none of them shall die intestate: the second, if he wishes that, as among them, the order of succession prescribed by the Twelve Tables shall be strictly preserved. 7 The person substituted in the place of a child under the age of puberty may be either named individually--for instance, Titius--or generally prescribed, as by the words 'whoever shall be my heir'; in which latter case, on the child dying under the age of puberty, those are called to the inheritance by the substitution who have been instituted heirs and have accepted, their shares in the substitution being proportionate to the shares in which they succeeded the father. 8 This kind of substitution may be made to males up to the age of fourteen, and to females up to that of twelve years; when this age is once passed, the substitution becomes void. 9 To a stranger, or a child above the age of puberty whom a man has instituted heir, he cannot appoint a substitute to succeed him if he take and die within a certain time: he has only the power to bind him by a trust to convey the inheritance to another either wholly or in part; the law relating to which subject will be explained in its proper place. TITLE XVII. OF THE MODES IN WHICH WILLS BECOME VOID A duly executed testament remains valid until either revoked or rescinded. 1 A will is revoked when, though the civil condition of the testator remains unaltered, the legal force of the will itself is destroyed, as happens when, after making his will, a man adopts as his son either an independent person, in which case the adoption is effected by imperial decree, or a person already in power, when it is done through the agency of the praetor according to our constitution. In both these cases the will is revoked, precisely as it would be by the subsequent birth of a family heir.