230 Zoological Society. 



that may fairly be attributed to our attaching too high a value to 

 characters purely structural or admensural, while we neglect others 

 more intimately connected with reproduction ; in a word, to the sub- 

 stitution of physical for physiological characters. In mammals, rep- 

 tiles and fishes, we have a primary division based entirely on physio- 

 logj^ : thus mammals are placental or marsupial ; reptiles are o\'ipa- 

 rous or spawning ; fishes are viviparous or spawning ; and this primary 

 divnsion of these classes is admitted by all physiologists to be strictly 

 natural. Notwithstanding, however, the purely physiological charac- 

 ter, on which these primary divisions depend, it is found that physi- 

 cal characters harmonise with physiological, and that intimate struc- 

 ture in each instance bears out physiological difference. It were not 

 wise altogether to discard structural differences even in the outset of 

 an inquiry into system, but it is necessary to use them rather as cor- 

 roborative than as indicative ; and above all to draw a distinct and 

 permanent hue between such as are truly intimate and such as are 

 purely adaptive. It has always appeared to me that one of the chief 

 advantages of an extensive Vivarium like that possessed by our Society 

 is the opportunity it affords for studying animated nature in an ani- 

 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 imcon- 

 nected that they cannot be 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 be 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, but 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, approacliing 

 her with alacrity when invited to partake of food she has discovered, 

 or hiding itself under bushes, 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- 



