This second species of the genus _Heterodera_ develops much like the beet eelworm, living like it on the roots of plants, but more deeply within them, so that the body of the female (which swells till it becomes pear- or flask-shaped) does not cause the outer part of the infested root to project, and does not reach the exterior. Where the eelworms collect, galls are formed which decay later on, when the eel-shaped larvæ escape into the soil, very soon, however, to enter the roots again at their slender tips. The galls are thickenings in the course of the root, and are never lateral appendages, like, for instance, the well-known “tubercles” in the roots of leguminous plants (_e.g._ clover, pea). The root eelworm lives in the roots of more than fifty plant species in the most various parts of the world, and infests both weeds and cultivated plants. It is especially damaging to clover and lucerne, in which not only the galls die, but also all parts of the root below them. In this country the roots of cucumber and tomato are sometimes attacked (E. A. Ormerod). CLASS: =PLATYHELMIA= (FLAT WORMS). Flat worms have a flat, generally leaf-like body, and usually no body-cavity, the space between the internal organs and the muscular body-wall being filled up with connective tissue. I will only deal here with the orders of Tapeworms (_Cestoda_) and Flukes (_Trematoda_). ORDER: =Cestoda= (TAPEWORMS). [Illustration: FIG. 135.—_Tænia saginata_: head, and a number of joints, represented natural size. ] [Illustration: FIG. 136.—The Common Tapeworm (_Tænia officinalis_): _a_, head and neck, strongly magnified; _b_, joints, natural size; _c_, eggs, strongly magnified. ] [Illustration: FIG. 137.—Tapeworm Larva (of _Tænia solium_), much enlarged. ] [Illustration: FIG. 138.—The three types of Bladder-worm, diagrammatically represented. ] [Illustration: FIG. 139.—Measle of _T. solium_, with head thrust out (× 6). ]