The subject was practically dormant for nearly a century and a half, largely owing to the dominance of classificatory botany under the in.fluen.ce of Linnaeus.
For further classificatory details, reference must be made to the special articles on the various orders.
Be that as it may, he declares that characters drawn from the sternum or the pelvis - hitherto deemed to be, next to the bones of the head, the most important portions of the bird's framework - are scarcely worth more, from a classificatory point of view, than characters drawn from the bill or the legs; while pterylological considerations, together with many others to which some systematists had attached more or less importance, can only assist, and apparently must never be taken to control, the force of evidence furnished by this bone of all bones - the anterior palatal.
Escaped the observation of Nitzsch, but he had scarcely used it as a classificatory character.
The new essays in this volume were mostly critical, but one of them, in which perhaps his guessing talent is seen at its best, "The Divisions of the Irish Family," is an elaborate discussion of a problem which has long puzzled both Celtic scholars and jurists; and in another, "On the Classificatory System of Relationship," he propounded a new explanation of a series of facts which, he thought, might throw light upon the early history of society, at the same time putting to the test of those facts the theories he had set forth in Primitive Marriage.