accident or occasion had caused to issue.[296] [Sidenote: Barons called by writ.] The ancient temporal peers are supposed to have been intermingled with persons who held nothing of the crown by barony, but attended in parliament solely by virtue of the king's prerogative exercised in the writ of summons.[297] These have been called barons by writ; and it seems to be denied by no one that, at least under the first three Edwards, there were some of this description in parliament. But after all the labours of Dugdale and others in tracing the genealogies of our ancient aristocracy, it is a problem of much difficulty to distinguish these from the territorial barons. As the latter honours descended to female heirs, they passed into new families and new names, so that we can hardly decide of one summoned for the first time to parliament that he did not inherit the possession of a feudal barony. Husbands of baronial heiresses were frequently summoned in their wives' right, but by their own names. They even sat after the death of their wives, as tenants by the courtesy.[298] Again, as lands, though not the subject of frequent transfer, were, especially before the statute de donis, not inalienable, we cannot positively assume that all the right heirs of original barons had preserved those estates upon which their barony had depended.[299] If we judge, however, by the lists of those summoned, according to the best means in our power, it will appear, according at least to one of our most learned investigators of this subject, that the regular barons by tenure were all along very far more numerous than those called by writ; and that from the end of Edward III.'s reign no spiritual persons, and few if any laymen, except peers created by patent, were summoned to parliament who did not hold territorial baronies.[300]