The Insessores are represented by a number of species.
Pp. 641-647) the denomination Insessores was changed to Altrices, and Grallatores to Praecoces - the terms now preferred by him being taken from Sundevall's treatise of 1835 already mentioned.
Birds being of all animals most particularly adapted for extended and rapid locomotion, it became necessary for him to eliminate from his consideration those groups, be they small or large, which are of more or less universal occurrence, and to ground his results on what was at that time commonly known as the order Insessores or Passeres, comprehending the orders now differentiated as Passeriformes, Coraciiformes and Cuculiformes, in other words the mass of arboreal birds.
Herein he divided the class A y es into two subclasses, to which he applied the names of Insessores and Grallatores (hitherto used by their inventors Vigors and Illiger in a different sense), in the latter work relying chiefly for this division on characters which had not before been used by any systematist, namely that in the former group monogamy generally prevailed and the helpless nestlings were fed by their parents, while the latter group were mostly polygamous, and the chicks at birth were active and capable of feeding themselves.