Branch Chordata 95 



Partly concealed by the lobes of the liver, find a small, 

 spherical, dark green body, the gall-bladder. Is it con- 

 nected with the liver and intestine ? Find somewhat 

 closely connected with this a long, irregular, pink- 

 colored body, the pancreas. Trace out the ducts of the 

 pancreas, gall-bladder, and liver as well as possible. 

 The red spleen is farther back in the abdominal cavity. 



VIII. — Respiratory System. Find the dark, thin-walled, 

 inflated bodies, the lungs, one on each side of the 

 heart. Through their walls runs a network of blood- 

 vessels, thus bringing the blood into close connection 

 with the air filling the lungs. In the floor of the 

 mouth, just back of the tongue, find the slit-like open- 

 ing of the larynx, a chamber which connects with the 

 lungs. Pass something down the larynx to see the 

 relation to the lungs. 



IX. — Reproductive System. The frog, like all vertebrates, 

 and many invertebrates, is unisexual, i.e. an individual 

 possesses but one kind of sexual organs. If the speci- 

 men is a female, large, irregular bodies, the ovaries, 

 will be found on each side of the posterior part of the 

 abdomen. Within these are found the cells which 

 develop into eggs. During the breeding season the 

 eggs pass from the ovary into the body cavity, and 

 from there to the exterior by oviducts. These are 

 coiled, tubular organs, with a funnel-shaped opening, 

 and they pass to the cloaca. The openings of the ovi- 

 ducts possess small cilia, whose vibrations guide the 

 eggs into them, and as the eggs pass through they 

 gather a mucus secreted by the walls of the duct. 

 This mucus swells greatly on striking the water, and 

 we may thus account for the appearance of the frog's 

 eggs when seen in ponds. 



