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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