§ 244. Certain of the _Protozoa_ are quite indefinite in their shapes, and quite inconstant in those indefinite shapes which they have--the relations of their parts are indeterminate both in space and time. In one of the simpler Rhizopods, at least during the active stage of its existence, no permanent distinction of inside and outside is established; and hence there can arise no established correspondence between the shape of the outside and the distribution of environing actions. But when the relation of inner and outer becomes fixed, either over part of the mass or over the whole of it, we have kinds of symmetry that correspond with the habitual incidence of forces. An _Amœba_ in becoming encysted, passes from an indefinite, ever-changing form into a spherical form; and the order of symmetry which it thus assumes, is in harmony with the average equality of the actions on all its sides. In _Difflugia_, Fig. 134, and still better in _Arcella_, we have an indefinitely-radial symmetry occurring where the conditions are different above and below but alike all around. Among the _Gregarinida_ the spherical symmetry and symmetry passing from that into the radial, are such as appear to be congruous with the simple circumstances of these creatures in the intestines of insects. But the relations of these lowest types to their environments are comparatively so indeterminate, and our knowledge of their actions so scanty, that little beyond negative evidence can be expected from the study of them. [Illustration: Figs. 131–139.] The like may be said of the _Infusoria_. These are more or less irregular. In some cases, where the line of movement through the water is tolerably definite and constant, we have a form that is approximately radial--externally at least. But usually, as shown in Figs. 137, 138, 139, there is either an unsymmetrical or an asymmetrical shape. And when one of these creatures is watched under the microscope, the congruity of this shape with the incidence of forces is manifest. For the movements are conspicuously varied and indeterminate--movements which do not expose any two or more sides of the mass to approximately equal sets of actions.[43]