TEOGS, TOADS, AND SALAMANDERS 233 



latory system. It is composed of three principal parts, 

 the muscular ventricle and two thin-walled auricles. The 

 blood is sent out from the anterior end of the ventricle 

 through a single artery, which gives off three branches on 

 each side. Four of these pass to different parts of the body 

 and end in capillaries The capillaries unite to form veins 

 through which the blood returns to the right auricle of the 

 heart. Of course this blood is impure and charged with 

 carbon dioxide. The remaining two branches carry blood 

 to the lungs and skin, where it is purified and returned to 

 the left auricle. The auricles empty their blood, both pure 

 and impure, into the ventricle. But by a compUcated 

 system of valves and by the manner in which the single 

 artery branches the two kinds of blood mix but little and 

 the purest blood is sent to the head, the next best to the dif- 

 ferent parts of the body, and the impure back to the lungs. 



The food and method of obtaining it. — The frog feeds 

 upon living, moving animals only; as worms, moths, flies, 

 beetles, etc. These are caught, while they are in motion, 

 on the end of the tongue as it is darted from the mouth with 

 great rapidity. The sticky, mucous secretion on the tongue 

 serves to hold the prey. The food is swallowed whole and 

 digested at leisure. 



Reproduction and life history. — When mature, the eggs 

 are set free in the body cavity and finally find their way into 

 the mouths of the oviducts.v In the passage through the 

 oviduct each egg becomes coated with a gelatinous ma- 

 terial which swells greatly when the egg reaches the water. 

 The eggs are deposited in large, irregular. Jellylike masses, 

 usually near the edges of pools and very often about the 

 stem of some plant (Fig. 163). After a number of warm 

 days each egg hatches into a black, wiggling object with an 



