By his will a testator, after making certain specific gifts, gave, devised, and bequeathed the residue of his estate to his trustees upon trust for conversion, and after payment thereout of his debts, funeral and testamentary expenses, to invest the residue and to stand possessed of such investments and of all parts of his estate for the time being unsold (thereinafter called his residuary estate)— (a) Upon trust to pay from the income thereof to his wife as and from the date of his death during her life so long as she should continue his widow an annuity of 400l., and to accumulate and invest the balance of income, and after her death or remarriage whichever event should first happen, then (b) upon trust to transfer and hand over his residuary estate, both corpus and income, invested as aforesaid, to his son absolutely, provided always that if his wife should die or remarry before his son attained the ago of twenty-one years, upon trust (with the exception of the sum of 2l. per week to be applied to the maintenance and support of his said son) to accumulate his residuary estate until his said son attained the age of twenty-one years, and then upon that event happening to transfer and hand over to his said son his residuary estate absolutely, and (c) in the event of his son dying before attaining the ago of twenty-one years upon trust "for my next of kin save and except my two sisters H. and I."