Page:Popular Science Monthly Volume 59.djvu/201

Rh of Cracow University, Russia, whose results form the basis of the following account :

The description of the life cycle may begin with the sporozoite, or youngest form, of the gregarine parasite. This is a small, elongate germ which makes its way through the fluids of the digestive tract of Ciona to the epithelial cells which line that canal, (l'ig. 1, A.) The sporozoite penetrates one of these cells and begins to grow at the expense of the cell contents, until, finally, too large for the cell host, it breaks the cell wall and falls into the lumen of the digestive tract, where it soon attains its full size. (Fig. 1, B. C. D.) It is now a comparatively large, sac-like cell, swollen at one end, and with a distinct nucleus. (Fig. 1, C.) After a longer or shorter period, not definitely determined, two adult forms come together and pour out a sticky, fluid substance, which soon hardens to form a common, firm covering, or cyst. (Fig. 1, E.) Each nucleus then begins to divide, and, after a multitude of daughter-nuclei have arisen, the protoplasm of the cell breaks np into as many parts as there are nuclei (Fig. 1, F. G. H.). These small protoplasmic parts (gametes) then wander out of the parent membranes and ultimately fuse, two by two, while still remaining in the original cyst wall (Fig. 1, I. J.). After the fusion, the nucleus and protoplasm in each double mass divides into eight parts, and a firm, enveloping membrane is secreted about them. This spore-membrane ultimately becomes impregnated with calcareous material, which thus forms a firm and resisting capsule for the eight germs within. Each germ is a sporozoite similar to the one which began the life cycle.

During the process of sporozoite-formation, the parasite is passed out with the fæces to the exterior. Here the original cyst ultimately bursts and liberates the multitude of spores with their contained sporozoites. The latter are well protected, however, by their calcareous shells, and do not suffer from the sea water or from drying. The spores may be finally taken into the digestive tract with food, and with this the opportunity for a renewed cycle is presented. The acids of the digestive fluids dissolve the calcareous coverings, and the eight sporozoites in each spore are liberated. The sporozoites again penetrate the epithelial cells, grow to maturity and repeat the process indefinitely.

In Coccidium, a parasite of some of the insects, the life history as worked out by Dr. F. Schaudinn differs in one or two important points from that of the gregarine.

Sporozoites are formed as in the previous case, and these work their way in a similar manner into the cells lining the digestive tract (Fig 3, a). Unlike the gregarine, the main period of their life is passed in these cells, and they drop into the lumen of the intestine only when they