After two bequests, each of an absolute interest in one-third of her property, to a niece and a nephew, testatrix bequeathed the remaining one-third of her estate to her husband ... to have and to hold subject to the request hereinafter stated. It, however, is my wish and desire and I charge my said husband ... to make disposition ... so that it will not pass to his heirs upon his death, but shall revert, after his death, to my heirs and be distributed to the legatees named in subparagraphs A. and B. of this clause Eighth ... subject, however, that my husband shall be at full liberty to use, have and keep all the income ... and so much of the principal and corpus as he may find convenient and desirable for his comfort, advantage and enjoy...