298 



ANATOMY AND PHYSIOLOGY OF THE FOWL 



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lungs, just as in the human system. (Refer to text-books on physi- 

 ology for a description of the human circulation.) 



Respiratory System. — Breathing is carried on in the lungs. The 

 air enters these through the trachea orwindpipe, which is a longtube, 

 dividing just before it reaches the lungs into two bronchial tubes, 

 one of which enters each lung. It is in the lungs that the blood 

 gives up the poisonous material which it has gathered, and takes 

 up its supply of oxygen to carry through the body. The lungs arc 



surrounded by large air sacs 

 -^ in the breast and abdomen, 

 there being nine in all. These 

 increase the size of the bird in 

 proportion to its weight and 

 enable it to fly better. 



Reproductive Systems. — 

 The female's reproductive 

 system consists of two main 

 organs, the ovaries and ovi- 

 duct. The hen has two ova- 

 ries, only one of which is 

 active. In general this re- 

 sembles a bunch of grapes, 

 the ova (or eggs) varying in 

 size from small specks to full- 

 size yolks, when the bird is 

 in condition for laying. Each 

 ovum (or egg) as it comes to 

 maturity enters the oviduct, 

 where it may be fertilized by 

 the sperm of the male; as it 

 passes down the oviduct suc- 

 cessive layers of albumin are 

 added, and finally just before 

 being laid the shell is put on. 

 A description of the formation of the egg is given in Chapter XVIII. 

 The reproductive glands of the male bird, called testicles, two 

 in number, are near the backbone just in front of the kidneys and 

 about opposite the last ribs. These secrete the male sperm, which 

 is transported through two tubes, called vas deferens, to the 

 cloaca (Fig. 144). 



The Development of the Senses. — The fowl has a well-devel- 



FiG. 144. — Male reproductive systeii 



