Page:Popular Science Monthly Volume 6.djvu/596

 578 their work is to destroy it. So, if the torula is not a mineral nor an animal, it must be a vegetable. Vegetables are the manufacturers or producers of protein; animals are the destroyers or consumers of it. You have now found that the torula or yeast-cell is a plant, and not an animal. The next question is, What kind of a plant is it? Mostly all plants need the sun, but the yeast-plant grows as well in the dark as in the light. Plants that need the light are always green; they take in carbonic acid, and give off oxygen, but the torula has no green color, and it takes in oxygen and gives off carbonic acid. Those plants which give off carbonic acid, grow in the dark, and are not green, are called fungi. The mushrooms and toadstools are fungi. Now let us see how many things you have learned about yeast: First, that it is alive; second, that it is a plant; third, that it is a fungus.

When first you try to study this lobster, you will perhaps think, as I thought, "How can I straighten out such a queer, crusty, clawy thing as that?" But, though the lobster looks as hard as the Greek alphabet, he is as easy as your own A, B, C, when once you find him out. You know the corolla or crown of the bean looked so hard, but it all came out nicely into five leaves, or petals, as soon as you knew how. Now let us see if we can find and name the different parts of the lobster. (You must have a real lobster before you to look at while I talk. The crawfish or crayfish that lives in brooks and rivers is fashioned after the lobster, only smaller; so one of these can be studied by those of you who live inland.) One thing is very certain—he has a great many different parts, very unlike each other. First, you see (Fig. 15), he is covered with a shell, which, like the mussel's and clam's, is his exo-skeleton. This shell is very hard, like stone, and it is colored purplish black with pale spots here and there. The lobsters which you see in shops are always scarlet. When these poor fellows are caught, they are plunged alive into boiling water, which turns the black coat red. This outside shell or exo-skeleton is made up of a great many different pieces, instead of two, as the mussel's; but those pieces are shaped and joined in such a way as to make three divisions of the body—a head, a thorax, or breastplate, and an abdomen. The head-piece of the shell is pointed in front, forming the beak or frontal spine (Fig. 15). Behind this head-piece is a groove or seam where the head joins the breast or thorax, making the two pieces of shell which cover the head and breast all one. So the first and second divisions of the body thus joined in one are called the