The larvæ of _Bilharzia_ closely resemble those of _Fasciola hepatica_, which latter may be appropriately noticed in this place. The ciliated embryo of the common liver fluke has the form of a long cone inverted; the anterior end or head being flatly convex. In the centre is a short proboscis-like papilla destitute of cilia (fig. 17). The general covering of cilia rests on a well-defined granular epidermis; this latter being succeeded by a dense peripheral layer of large nucleated cells, each of them measuring about 1/2500″ in diameter. The epidermis measures 1/6250″ in thickness. In the central mass of parenchyma no internal organs are recognisable, but Leuckart observed indications of a canal which he thought might open at the tail, though the opening itself was not actually visible. As long as the ciliated covering remains intact the embryo, like other animalcules, displays great activity, whirling round and round on its own axis, and also describing gyrations and circles of different degrees of range in the water, the latter movements being accomplished by bending the body upon itself to a greater or lesser curvature. The embryos of _Bilharzia_ and other infusoria exhibit the same behaviour, and, as Leuckart observes, when these embryos knock against any obstruction, they pause after the blow, as if to consider the nature of the substance they have touched. As in the case of fluke embryos generally, the ciliated covering eventually falls off and the embryo reassumes a more or less oval figure, at the same time changing its swimming mode of progression for the less dignified method of creeping. In the free ciliated condition the embryo of the common liver-fluke measures, according to Leuckart, 1/190″ in length, the anterior broad end being 1/500″. The cilia have a longitudinal measurement of 1/1388″.