2. Posthumous children are entitled to take by descent as if they had been born at the time of their deceased ancestor. When a father has made a will without providing for a posthumous child, such a will is in some states, as in Pennsylvania, revoked pro tanto by implication. 4 Kent, Com. 506; Dig. 28, 5, 92; Ferriere, Com. h. t.; Domat, Lois Civiles, part 2 ' liv. 2, t. 1, s. 1: Merl. Rep. h. t.; 2 Bouv. Inst. n. 2158.