ABSTRACT
As the highest life is found in the most complicated environments, so, conversely, the lowest life is found in environments of unusual simplicity. Most environments present both coexistences and sequences; but there are some that during a limited period, present coexistences only; and in these, during this limited period, occur the organic forms to which, by common consent, is assigned the lowest place, both in respect of structure and vital properties. Of those classed with the vegetable kingdom, may be instanced the yeast-plant, and the Protococcus nivalis (red snow fungus). Of those held to be of animal nature, the Gregarina , and the parasitic cell which causes smallpox, may be taken as samples. The processes by which the movement is effected, are themselves in direct and almost homogeneous correspondence with certain almost ever-present properties of the environment.
