94 Laboratory Guide in Zoology 



v.- — Blood System. Just beneath the position of the 

 chest bones the heart may be seen. It is a cone-shaped 

 body, darker at the apex. There are only three cham- 

 bers, — one ventricle and two auricles. The ventricle 

 forms the apex of the cone and has walls much thicker 

 than those of the auricles. Give reasons for this. 

 Notice that there is no blood fluid in the body cavity. 

 The blood circulates in a closed system, passing from 

 the heart in arteries and returning in veins, instead of 

 being left to find its way back to the heart by con- 

 tractions of the body. Observe the large vessels leaving 

 the heart ; the arteries cannot be easily distinguished 

 from the veins. Follow the vessels as far as you can 

 without disturbing the other organs. 



VI. — Digestive System. Without removing the viscera, 

 study the entire alimentary tube and its appendages, 

 with the aid of the following directions : Move the jaws 

 up and down. Do they move in the same direction as 

 the jaws of insects or crustaceans move ? Notice the 

 attachment of the tongue at its anterior end. The 

 posterior end is moistened by a sticky secretion from 

 the roof of the mouth, and protruded for the prehen- 

 sion of food. The mouth opens into the oesophagus, 

 and thence into the stomach — the elongated, thick- 

 walled enlargement of the tube. Pass some blunt 

 instrument down the oesophagus, or inflate with a 

 tube to observe the relation of the mouth, oesophagus, 

 and stomach. From the stomach follow out the small 

 intestine, large intestine, and cloaca, the last enlarge- 

 ment. Into the cloaca pass the contents of the repro- 

 ductive organs. 



VII. — Appendages of the Tube.' Find the liver, a dark- 

 lobed, very conspicuous body, lying near the heart. 



