The mesogloea is more abun dantly developed in the free-swimming forms, and contains special mesogloeal corpuscles, derived by immigration from the ectoderm, and generally occurring in the form of stellate or bipolar cells.
The vegetation of the dry region of central Asia is remarkable for the great relative number of Chenopodiaceae, Salicornia and other Central salt plants being common; Polygonaceae also are abun Asia.