47 
mated state, for ascertaining physiological as well as physical charac¬ 
ters. If then we avail ourselves of the opportunities which are or 
ought to be thus afforded us, we shall find that in the very outset of 
life a physiological character of the most obvious kind will divide birds 
into groups as distinct as are the placental and marsupial mammals, 
or the cartilaginous and bony fishes. Prior to the extrusion of the 
egg, observed facts bearing on this subject are so few and so uncon¬ 
nected that they cannot he rendered available as affording evidence 
on the question to be considered; it is therefore compulsory that our 
comparisons begin at that moment when the condition of the young 
becomes patent by the breaking of the shell. Commencing the inquiry 
at this point, which may safely he regarded as analogous to the birth 
of a placental animal, we have this obvious grand division of the 
class :—- 
1. Hesthogenous Birds. —In these, immediately the shell is broken 
the chick makes its appearance in a state of adolescence rather than 
infancy: it is completely clothed, not with such feathers as it after¬ 
wards wears, hut still with a close, compact, and warm covering: it pos¬ 
sesses the senses of sight, hearing, smelling, &c. in perfection : it runs 
with ease and activity, moving from place to place at will: it perfectly 
understands the signals or sounds uttered by its parent, approaching 
her with alacrity when invited to partake of food she has discovered, 
or hiding itself under hushes, grass, or stones, when warned of danger; 
in either case exhibiting a perfect and immediate appreciation of its 
parent’s meaning : it feeds itself, pecking its food from the surface of 
the earth or water, and not receiving it from the beak of its parent: 
although entering on life in this advanced state, it grows very slowly, 
and is long in arriving at maturity. When full-grown it uses its feet 
rather than its wings : it trusts much to its legs for means of escape : 
when it flies, it moves through the air by a series of rapid, powerful, 
laboured strokes of the wing, and invariably takes the earliest oppor¬ 
tunity of settling on the land or water, not on trees; it never takes 
wing for recreation or food, but simply as a means of moving from 
place to place : it is polygamous in its habits ; the number of females 
predominating over the males : the males are pugnacious, they accom¬ 
pany the females only until incubation has commenced, and abandon 
the duties of incubation and the care of the young solely to the 
females : the females make little or no nest, a depression scratched on 
the surface of the soil generally sufficing: the eggs are large in com¬ 
parison to the size of the bird : neither sex sings, or attempts to imi¬ 
tate the voice of men or animals. Birds included in this division 
approach more nearly to mammals than do those which it excludes : 
for instance, the habitual use of land or water for progression, the 
swiftness of foot, the strength and muscular development of the legs, 
the polygamous habits, the want of the extraordinary instinct of nest¬ 
making, are characters which, while they seem to degrade these birds 
as birds, certainly raise them in the list of animals, because they are 
thus brought nearer those animals which suckle their young, and which 
are always placed at the head of the animal kingdom. In an econo- 
