Toward the posterior end of the body cavity are two long, dark-red glands, the _kidneys_, which are the principal excretory organs of the body. Through a long, slender tube (the _ureter_) each of the kidneys passes off its wastes. Where do the ureters open? Anterior to the kidneys are the reproductive organs. The eggs, produced by the female snake, after being fertilized, pass backward through the egg-tubes. During the breeding season these tubes are much distended. This is due to the presence of the developing eggs, for the young snakes are hatched in the egg-tubes. A successful injection as directed in the first technical note will have filled both arterial and venous systems. How does the general shape of the snake's _heart_ compare with that of the toad? The heart consists of two _ventricles_, incompletely separated, and _two auricles_. In the snake the _conus arteriosus_ is very much shortened and is not visible. Note two large vessels arising from the median portion of the ventricle. The one on the left side is the _left aortic artery_ or _left aortic arch_, while the right gives off two branches. Where does the anterior one of these run? The main branch, or _right aortic arch_, passes back to meet its fellow, the left aortic artery, forming with it the _dorsal aorta_, which runs posteriorly to the end of the tail. Note the various branches given off by the dorsal aorta and trace some of them. Arising from the ventricles beneath the two aortic arches is the _pulmonary artery_, which goes to the lung. There the blood is purified, after which it is taken up by the _pulmonary vein_ and carried back to the left auricle, whence it passes into the ventricle to be mixed with the impure blood from the right auricle. From the arteries the blood flows to all parts of the body through fine _capillaries_, bathing the tissues, giving off oxygen and taking up the carbonic acid gas. From these capillaries it passes into veins and so back to the heart; from the anterior end of the body through the _jugular veins_ and from the posterior portion of the body through the _postcaval vein_. Flowing forward from the tail in the _caudal vein_, the blood enters the capillaries of the kidneys, where the waste matter is taken from it. This part of the circulatory system is known as the _renal-portal_ circulation. From the kidneys the blood flows through the postcaval vein anteriorly to the heart. The blood which passes out from the dorsal aorta to all parts of the alimentary canal is again collected into veins which unite to form the _mesenteric vein_. This vein runs to the liver, where it breaks up into capillaries. Thence the blood is carried into the postcaval vein, which leads directly to the heart. This part of the circulatory system which collects blood from the alimentary canal and carries it to the liver is called the _hepatic-portal_ system.