256 ANATOMY OF VERTEBRATES. 



Apteryx the largest: in this species it weighs 14 J oz. ; the entire 

 bird 60 oz. ; so that the egg is nearly equal to one-fourth of the 

 parent. The hugest known egg of a bird is that of the extinct 

 j^'pyornis of Madagascar. The following are comparative ad- 

 measurements of this ^^^ and that of an Ostrich : — 



Length of majoi- axis 



„ „ minor axis 



Greater circumference 



Smaller circumference 



The contents of the ^gg of the iEpyornis are computed to equal 

 those of 6 Ostriches' eggs, and 148 hen's eggs. 



The eggs of most Owls, of some Penguins ( Spheniscus), of the 

 King-fishers {Alcedo, Halcyoii), of the Plantain-eaters (Muso- 

 phaya), and Bee-eaters {Merops), are those that have, or nearly 

 approach to, the spherical shape : those that furthest depart from it, 

 or have the longest shape, are the eggs of the IMegapode and Al- 

 batross. The oval, or ovate, is the common form in birds (fig. 130, 

 and vol. i. p. 599, fig. 420, c) : the eggs with the narrowest small 

 end, ib. D, are those of the Plovers, Snipes, Sand-pipers and allied 

 Waders, which usually lay four eggs, packed in the smallest 

 compass by the meeting of the small end of each in the centre. 

 The egg of the Chinese Jacana {Parra sinensis) is like a top in 

 shape. The eggs of Grebes, Cormorants, Pelicans, are elliptic. 

 The shell of the Emeu's and Ostrich's egg has a rough exterior : 

 that of the Gangas {Pterocles) has a glossy smoothness. The 

 shell of the egg of the Ostrich, Emeu, and Cassowary is rela- 

 tively thicker than that of the Apteryx, Mound-bird, and Dinornis. 



§ 170. Accessory Generative Structures and External Sexual 

 Characters. — The exception to the rule of incubation is given by 

 the Megapodial birds of the Australasian Islands. A huge mound 

 of decaying vegetable matter is raised: the eggs are deposited 

 vertically in a circle at a certain depth, near the summit, and 

 the chick is developed with the aid of the heat of fermentation. 

 The large size of the egg relates to affording a supply of material 

 sufficing for an unusually advanced state of developement of the 

 chick at exclusion ; whereby it has strength to force its way to the 

 surface of the hatching-mound, with wings and feathers sufficiently 

 developed to enable it to take a short flight to the nearest branch 

 of an overshadowing tree.^ 



A steady continuous temperature of about 100° Fahr. is the 



' Lvi'. and LViir. 



