Sheep and the hog are more tormented with cysted worms than any other domestic animals used for food. If introduced into the human intestines by eating raw ham or sausages, the larvæ soon acquire the perfect form. The eggs of the Tænia may be introduced into the human or animal stomach; for dogs and other carnivora which eat raw unwholesome meat are infested by full grown tænia, which fix themselves to their entrails by their hooks and suckers, while at the same time egg-bearing segments separate successively from their posterior extremity, and being voided scatter the eggs far and wide on land and in water. The young of some Entozoa undergo various transformations, as those of the Distoma of the Lymnæa. When full grown that entozoön is like a sole, flat, broad, and long, with a kind of head at the broad end, and two suckers on its under-surface, in one of which there is a pore serving as a mouth, whence an alimentary canal extends, which spreads in branches almost throughout the whole body. This animal has a filamentary nerve round its gullet, from which minute fibres pass to the mouth, and two filaments extend backward on each side as far as the second sucker. The eggs which occupy the whole margin of the body are developed into worms, each of which seems to be merely a mass of structureless cells enclosed in a contractile case. By a second change each of these cells is transformed into a freely swimming ciliated zooid endowed with eyes. Having escaped from their contractile case, they remain for a time in that state, and then imbed themselves in the mucus on the foot of the fresh-water mollusk Lymnæa, or pond snail, where they are transformed into true Distomata, and ultimately enter into the body of the Lymnæa itself, where they lose their eyes and cilia, which are no longer of use in their dark and permanent abode. The Fluke found in the livers of sheep that have the rot is a Distoma.