But the biological unit, the cytode or enucleated cell, is a very complex body compared to a molecule of protoplasm. The phenomena of heredity show that there are still simpler elements or units having very varied qualities. These are probably not simple molecules of protoplasm, although these need not be assumed to be altogether alike, but would appear to be multiform aggregations of such molecules carrying in their composition the hereditary tendencies of ancestral organisms. The Protozoa and Protophyta, or Protist kingdom, are unicellular organisms, and their organization is in a sense molecular. At least they are devoid of true organs and even of true tissues.
Biotic organization proper consists of some kind of combination of the biological units or cells into tissues and organs, thus forming a compound or complex body called an organism. Such combinations are formed in a great variety of ways and the primary units are integrated in all degrees. In the highest organisms there is complete integration and interdependence of parts. Every organism is held together and rendered effective entirely by protoplasm, every organ and part being linked to every other by threads of this substance called nerves. The. life of plants is as dependent upon protoplasm as that of animals, but the protoplasm resides in the cells and controls the vegetative processes. The important fact from our present point of view is that every living organism is an organized mechanism for the storage and voluntary expenditure of energy, and as such does not differ in principle from the chemical products of the inorganic world. The force that resides in the organic world is all derived from the properties of protoplasm, and these are in turn derived from chemical affinities. We might carry the series back and find that all energy originally emanates from the primary forces of gravitation and radiation which permeate the universe. The reason why a developed organism has more power than an undeveloped cytode is that a much larger amount of protoplasm has been coordinated into an economic system and made to exert its force in unison. Its entire combined energy may be directed at will to a single purpose. The system is more-
