136 CLASS AVES. 



has provided for this inability by rendering it oviparous ; and that 

 the eggs, which have a shell that does not give way, unlike the 

 eggs of reptiles, which are soft, may be more easily laid, birds 

 have the ossa ischia, and the ossa pubis, remarkably prolonged 

 behind. In this large cavity of the pelvis the eggs acquire their 

 volume, and the white which surrounds the vitellus. 



The ovaries of the female are tolerably large, and situated 

 near the reins. An oviductus receives the vitellus, which is 

 enveloped in an albuminous substance, commonly denominated 

 the Avhite. AVhen the egg descends to the lower part of the 

 oviductus, it begins to be covered Avith a cretaceous matter, 

 the thickness of which increases in the cloaca, whence the egg 

 is finally expelled by the action of the peculiar muscles of this 

 part. The colour and form of the egg-shell vary in the dif- 

 ferent species, and form a criterion of distinction, which im- 

 peratively claims the attention of naturalists. If the ovule has 

 been fecundated in the act of coition, the heat produced by 

 incubation is sufficient for the developement of life. Among 

 our domestic fowls, where the developement has been investi- 

 gated with the greatest accuracy, it has been observed, that at 

 the end of six hours a small red point appears on the vitellus. 

 This is the punctum saliens, which is to be the heart of the 

 chicken. From this punctum saliens proceed numerous radia- 

 tions of vessels, which are, as it were, the outlines of the venous 

 system. A small crescented gray line which surrounds the 

 little red point, becomes the spinal-marrow. It inflates in front 

 to form the brain. The legs, then the arms, and, finally, the 

 viscera, are developed. 



The eggs are usually of an elliptical form, more or less 

 elongated, according to the species. There is a large and a 

 small end ; the first is rounded, and the other approximates to 

 a point. In the majority of birds, the eggs are of one predomi- 

 nating colour, over which are dispersed spots more or less 

 numerous, and more or less varied. These spots augment in 

 size, and become deeper in colour, according to the progress of 



