“There is a muscle,” continued Book, “fastened at the dark spot on each valve. It becomes very strong by use. An oyster knows how to let it stretch, thus opening the valves to allow water to enter his chamber. It also knows how to draw it up so as to close them to keep out intruders. The white covering over the body is called the ‘mantle’. If you notice the inside of an oyster valve, you can see a mark showing how near to the edge the mantle came. That is called the pallial line. “If you will keep on looking you will succeed in finding that besides a mouth an oyster has a stomach, liver and intestines, a nervous system, and a heart that pumps blood, though it is not red but white blood. “When you breathe, you take in your lungs from air what is called oxygen. Without oxygen there can be no life. Anything that can not in some way take in oxygen can not have life. Water as well as air contains it. Oysters have no lungs, but they have leaf-like gills on each side of the body. By means of these they get oxygen.” “Can an oyster see?” asked Willis. “It has organs of sight, hearing, smelling, touch.” “Where are his eyes? We could not find them.” “Hunt them again,” laughed Book. “I think that I will not tell you that. Since an oyster has no head you must not be surprised to find them in an odd place. The dark part which you noticed this afternoon and which shows so plainly in a cooked oyster is its great liver.” “To-morrow I will again try to find eyes. Perhaps auntie will let me take her glass.” Stepping near and pointing as he talked, Book continued: “To protect her soft body, friend Mrs. Oyster’s mantle produces a shell of lime which grows by being enlarged around the edge. The high point on the left valve is called the beak. If you will scrub her shell with a brush to-morrow you will see lines running around the beak in the same direction as the margin. These are called ‘lines of growth.’ By them oystermen can tell the age of the shellfish.” “How strange!” said Willis thoughtfully. “Tree trunks also show lines of growth.” “Where did you come from?” asked Willis of Mrs. Oyster. “As I have lived most of my life within this narrow shell,” she answered with a cast-down air, “I have no idea where I came from nor where I now am. Shall I tell you the story of my life?” “Yes, do, please. It must be interesting. You are such an odd creature.”