Complex sentence: Patronymic forms of personal names beginning with element "Giolla" "servant of" (example: MacGillchrist) underwent a transformation of their own: the prefix "Mac" and the element "Giolla" were contracted into "Myley".
Split into simpler sentences: Patronymic forms of personal names beginning with element "Giolla" "servant of" (example: MacGillchrist) went under a transformation of their own. The prefix "Mac" and the element "Giolla" were contracted into "Myley".