EGGS AND NESTLINGS 
parents much more closely than do the newly hatched 
young of the majority of the Amphibia. No bird is 
Ovoviviparous, as are some reptiles. Moreover, as a 
very general rule the eggs of birds are not merely dropped 
promiscuously, but laid, sometimes even in a regular 
position, in definite nests; these nests are often com- 
plex structures of some architectual pretensions. The 
eggs are for the most part coloured, while the eggs of 
reptiles are never coloured, but always white. A good 
many birds also lay white eggs. While a reptile emerges 
from the egg in the likeness of its parents, the young 
bird does show some differences from its parents, though 
these are never of a kind such as to justify the use of the 
term larva for a newly hatched bird. The only sugges- 
tion of a larval form among birds is perhaps the Hoatzin, 
where the mobile fingers with well developed claws at 
the ends are organs modified for the purposes of the 
nestling, and thus just come under the category of 
what is meant by a larva. All these facts, except per- 
haps the last, are familiar enough to every one; but it 
is just as well to emphasize them in order to point out 
the distinctions between birds and other vertebrated 
animals. Newly hatched birds differ in different cases. 
In some species they are completely nude and devoid of 
feathers. In others they are covered with down, which 
is shed by being thrust up upon the tips of the subse- 
quently produced nestling plumage, which itself gives 
way later to the final and annually deciduous plumage. 
‘The twittering and “cheeping’”’ of the young is 
succeeded in many birds by a most elaborate voice, 
produced by the movement of a vibrating membrane 
at the junction of the two bronchi, into which the at 
first single air tube (trachea), leading to the lungs, 
divides. More is said of the bird’s voice later. In the 
meantime, it is as well to note that the possession of 
a voice of the kind which reaches its maximum for 
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