THE 3iov.se 437 



man by the "Adam's apple." The wall of the windpipe 

 (trachea) contains small rings of cartilage which serve to sup- 

 port it and prevent its collapse on exhalation of the breath. 

 Below, the trachea divides into two tubes (bronchi), one of 

 which goes to each lung. Here it divides repeatedlj-, and 

 finally the smallest branches open into a thin-walled air vesi- 

 cle called a lobule of the lung. The wall of the lobule is cov- 

 ered with a network of blood capillaries, and here oxygen 

 passes from the air to the blood. 



Organs of Excretion. — The kidneys are a pair of oval, bean- 

 shaped bodies lying close to the dorsal wall of the abdominal 

 cavity. As in the pigeon, the kidnej^ is a mass of tubules each 

 associated with a capillary network where the waste products 

 pass from the blood to the cavity of the tubules, whence they 

 are collected in the central cavity of the kidney, and thence 

 conducted by the ureters to a single urinary bladder, which is 

 periodically emptied. 



Organs of Reproduction. — The male and female germ glands 

 — testes and ovary — are small organs lying in young animals 

 in the dorsal part of the abdominal cavity. The products are 

 carried by special tubes to the exterior — the sperm ducts 

 and the oviducts. The eggs are of small size and not sur- 

 rounded with allnmiinous and limy covering, as in birds, nor is 

 there much food yolk. The reason for the difference is that, 

 whereas the eggs of birds, developing independently of the 

 mother, must be supplied with a protective covering and a 

 supply of food-stuff, the egg of the rabbit is not only fertilized 

 in but develops in the oviduct, is protected by the maternal 

 body, and is sujDplied with food from the maternal blood- 

 vessels. Only after the embryonic rabbit has become well 

 developed, has gained its coat of hair, and is almost ready to 



