Butschli''s studies on protoplasm contributed in an important way to the investigation of protoplasm considered as a colloidal system and to the breakdown of fibrillar conceptions of protoplasm-structure; but on their more theoretical side some of his main conclusions have been outgrown. Protoplasm often does show a finely alveolar structure, and the appearance of a fibrillar network in fixed protoplasm is in most cases, if not in all, either an optical illusion or a coagulation-artifact. On the other hand, the visible alveolar or emulsion-like structure is neither a primary nor a universal characteristic of protoplasm. It may arise secondarily in protoplasm that is originally nearly or quite optically homogeneous; it is not a simple, diphase system; nor can Biitschli''s "finer" or "true" structure be distinguished logically from the coarser or secondary ("pseudo-alveolar") one arising by the close crowding of larger bodies or drops (yolk, secretory granules, vacuoles, etc.). The dispersed bodies generally vary widely in size, chemical and physical nature, function and grouping. In respect to size, Biitschli''s "finer" structure lies near the upper end of a series of which the limit is shown in the "coarser" or secondary structure and the lower in the ultra-microscopical dispersed particles of the hyaloplasm. In the sea-urchin (Arbacia) the visible dispersed bodies are of at least 5 types clearly distinguishable by their reactions to dyes and to osmic acid, by centrifuging, and otherwise. These are the yolk or alveolar spheres, the chromatophores or pigment granules, the fat drops, the mitochondria, and the Golgi-bodies (of which there are several modifications). By the progressive multiplication and crowding of these bodies during the growth of the oocyte is built up the alveolar structure. It is an important but unanswered question which of these bodies arise de novo (i.e., without direct relation to pre-existing ones of the same kind) and which, if any, are permanent components of the cytoplasmic system. In any case no present logical ground exists for excluding the formed bodies ("inclusions") from the "living" stuff or protoplasm. The term protoplasm does not designate a single substance but is a collective name for the sum-total of the active components that cooperate in the work of a complex system; and life is the sum-total of the activities of that system.