Section 25. If a child, or the issue of a child, omitted in the will takes under section twenty a portion of the estate of a testator, such portion shall be taken from all the devisees and legatees in proportion to and not exceeding the value of what they respectively receive under such will, unless in consequence of a specific devise or legacy or of some other provision of the will a different apportionment is found necessary to give effect to the testator’s intention relative to that part of his estate which passes by his will.