The life-history of all of these is very similar, the principal difference being in the length of time it takes them to sporulate. Let us begin with the parasite after it has been introduced into the blood and trace its development there. At first it is slender and rod-like in shape. It has some power of movement in the blood-plasm. Very soon it attacks one of the red blood-corpuscles and gradually pierces its way through the wall and into the corpuscle substance (Fig. 99); here it becomes more amoeboid and continues to move about, feeding all the time on the corpuscle substance, gradually destroying the whole cell. As the parasite feeds and grows there is deposited within its body a blackish or brownish pigment known as melanin. During the time that the parasite is feeding and growing it is also giving off waste products, as all living forms do in the process of metabolism, but as the parasite is completely inclosed in the corpuscle wall these waste products cannot escape until the wall bursts open. After about forty hours if the parasite is _vivax_ or about sixty-five hours if it is _malariæ_ it becomes immobile, the nucleus divides again and again and the protoplasm collects around these nuclei, forming a number of small cells or spores, as they are called. In about forty-eight or seventy-two hours, depending on whether the parasite is _vivax_ or _malariæ_ the wall of the corpuscle bursts and all these spores with the black pigment and the waste products that have been stored away within the cell are liberated into the blood-plasm. [Illustration: FIG. 99--Diagram to illustrate the life-history of the malarial parasite. 1 is a red blood-corpuscle, 2 to 7 shows the development of the parasite in the corpuscle, _a_ _b_ _c_ _d_ and _a´_ _b´_ _c´_ and _e_ the development of the parasite in the stomach of the mosquito, _f_ _g_ _h_ _i_ the development in the capsule on the outer wall of the stomach of the mosquito, _k_ in the salivary gland.] [Illustration: FIG. 100--Malarial mosquito (_A. maculipennis_) on the wall.] [Illustration: FIG. 101--Malarial mosquito (_A. maculipennis_) standing on a table.]