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.
In the course of this series, however, he saw fit to alter the name of his two subclasses, since those which he at first adopted were open to a variety of meanings, and in a communication to the French Academy of Sciences in 1853 (Comptes rendus, xxxvii.
Pp. 50-71), was found to be established on a single character of the feet only; though he was careful to point out, immediately after formulating the definition of his subclasses Constrictipedes and Inconstrictipedes, that the former " make, in general, compact and well-built nests, wherein they bring up their very weak, blind, and mostly naked young, which they feed with care, by bringing food to them for many days, until they are fledged and sufficiently strong to leave their nest," observing also that they " are principally monogamous " (pp. 55, 56); while of the latter he says that they " make either a poor and rude nest, in which they lay their eggs, or else none, depositing them on the bare ground.
At hatching far more developed than are those of the herons or the cormorants; and, in a general way, nearly every one of the asserted peculiarities of the two subclasses breaks down under careful examination.
Newton accepted the three subclasses of Huxley, Saururae, Ratitae and Carinitae, and made a series of cautious but critical observations on the minor divisions of the Carinates.
In 1816, de Blainville, 4 adopting Latreille's view, divided the Linnaean Amphibia into Squamiferes and Nudipelliferes, or Amphibiens; though he offered an alternative arrangement, in which the class Reptiles is preserved and divided into two subclasses, the Ornithoides and the Ichthyoides.
Where a further subdivision is desirable without descending to the next lower term of grouping, the prefix "sub" is made use of, so that a class may be divided first of all into subclasses each of which is divided into orders, and an order into sub-orders each of which bears a group of families.