3417. The Bird is thoroughly, or "out-and-out" organized as an animal of song. In it Nature attains unto a definite hearing and speech. The Bird speaketh the language of Nature.
With the Bird, the voice, properly speaking, breaks forth for the first time, and that too in a high grade of perfection, as melody.
3418. The ear is the highest representation of the trachea in muscles and bones. The Bird is the Otozoon.
Sexual Parts.
3419. The kidneys are symmetrically constructed, although not yet a perfectly coherent mass. They are of very large size. But a strange feature has come to pass in the urinary cyst, which is the sexual lung. Into this, as has been already said, the intestine opens, and thus it here again passes over into the lung, just as it has passed over into a fleshy cardioid stomach, and completely upwards into the feather-like tongue.
Into this sexual lung the seminal ducts also enter, or the penis, when one is present, along with the oviduct.
3420. The ovum consists of two completely separated substances, and these indeed are so distinct, that the vitellus is secreted at an entirely different place to the albumen, the former in the ovarium, the latter in the oviduct—whereas in Fishes both originated together.
The separation cannot extend further, or else the substances would no longer unite with each other, and the vitellus must be first mixed with the albumen, after it has been completely formed, after or when it is an embryo. In the Bird albumen and vitellus come together during their passage out of the parent's body, or in the act of being laid, and thus before the albumen has been converted into the chick. But in the Mammalia they are first completely united, subsequently to their being laid—i. e. during the period of lactation.
3421. The vitellus is directly secreted from the arteries, but the albumen from an enteroidal sac or the oviduct, which is finally converted into mammary glands.
3422. The vitellus is more a product of the thorax, and is therefore formed directly into the intestine and entire embryo.