When a capsule splits in two under the influence of the internal osmotic pressure, it may happen that the operculum or upper valve floats away in the liquid. We thus obtain a free swimming organism, a transparent bell-like form with an undulating fringe, like a Medusa. [Illustration: FIG. 54.--Capsular osmotic growth, the two valves separated showing the colloidal contents.] Frequently a single seed or stock will give rise to a whole series of osmotic growths. A vesicle is first produced, and then a contraction appears around the vesicle, and this contraction increases till a portion of the vesicle is cut off and swims away free like an amoeba. The same phenomenon may be observed with vermiform growths, a single seed often giving {141} rise in this way to a whole series of amoebiform or vermiform productions. It must be remembered that in an osmotic growth the active growing portion is the gelatinous contents in the interior, the external visible growth being only a skeleton or shell. We may sometimes succeed in hooking up one of these long vermiform growths, breaking the calcareous sheath, and drawing out a long undulating translucid gelatinous cylinder. The outline of this cylinder is so well defined as to make us doubt whether the fine colloidal membrane which separates it clearly from the liquid can have been formed so rapidly, or if it may not perhaps exist already formed in the interior of its calcareous sheath. [Illustration: FIG. 55.--Microphotograph showing the structure of various osmotic stems. (Magnified 25 diameters.) (_a_) Sodium sulphite. (_b_) Potassium bichromate. (_c_) Sodium sulphide. (_d_) Sodium bisulphite. ] When a large capsular shell such as we have described bursts, it expels a part or the whole of its contents as a gelatinous mass which retains the form of the cavity. Similarly, if we suddenly dilute the mother liquor around an osmotic cell, it bursts by a process of dehiscence, and projects into the liquid a part of its contents, which may thus become an independent vesicle. In this way a single osmotic cell may produce a whole series of independent vesicles. It is even possible to rejuvenate an osmotic growth that has become degenerate through age. An osmotic production grows old and dies when it has expended the osmotic force contained in the interior of its capsule. A calcium osmotic growth which has thus become exhausted may be rejuvenated by transferring it to a concentrated solution of calcium chloride. It will absorb this, and thus be enabled to renew its evolution and growth when put back again into the original mother liquor. {142}