10 ELEMENTARY ZOOLOGY 



which has passed through the systemic arteries and body 

 capillaries is collected again into other vessels going back 

 to the heart; these are the veins, which empty into a large 

 thin-walled reservoir, the sinus venosus, which in turn 

 connects with the right auricle of the heart. Three large 

 veins enter the sinus venosus, namely, two pre-caval veins 

 at the anterior end, and a single post-caval vein at the 

 posterior end. Trace out the larger arteries and veins 

 from the heart to their division into or origin from the 

 smaller vessels. 



TECHNICAL NOTE. Carefully remove the heart together with 

 the lungs. The lungs may be inflated by blowing into them through 

 the laryngo-tracheal chamber with a quill and tying them tightly, 

 after which they should be left for several days to dry. When 

 perfectly dry, sections may be cut through them in various places 

 with a sharp knife, and by this means a very good idea of the 

 simple lung structure of the lower backboned animals can be ob- 

 tained. With a sharp knife cut the heart open, beginning at the 

 tip (ventricle) and cutting up through the conus arteriosus and 

 the two auricles. Note the valves in the heart which separate 

 the different compartments. 



Note on either side of the median line in the dorsal 

 region a pair of reddish glandular bodies (the kidneys). 

 From each kidney trace a tube (itreter) posteriorly toward 

 the region of the anus. The kidneys are the principal 

 excretory organs of the body. The blood which flows 

 through the delicate blood-vessels in the kidney gives up 

 there much of its waste products. These pass out through 

 small tubules of the kidneys into the ureters, which carry 

 the wastes toward the anus. Along one side of each 

 kidney may be seen a yellowish glistening mass, the 

 adrenal body. 



In some of the specimens studied, the body cavity may 

 be filled with thousands of little black spherical bodies. 

 These are undeveloped eggs. They are deposited by the 

 mother toad in the water in long strings of transparent 

 jelly, which are usually wound around sticks or plant- 



