91. _The Exoplasm or Extracapsular Protoplasm._--The extracapsular protoplasm, which may be shortly termed the "exoplasm" (or ectosarc), is primitively in all Radiolaria (and especially in their earliest development stages) the only important constituent of the extracapsulum, besides the calymma. Although the extracapsular and intracapsular protoplasm of the Radiolaria are everywhere in direct communication, and although the openings in the membrane of the central capsule bring about an interchange between them, still the two portions of sarcode show certain constant and characteristic differences, which are due to the physiological division of labour between the central and peripheral parts of the body and their corresponding morphological differentiation. The extracapsular, like the intracapsular, protoplasm is originally homogeneous, but may afterwards become differentiated in various ways, producing the special constituents of the extracapsulum. Such "external protoplasmic products" are vacuoles, pigment-bodies, &c. More important, however, are the topographically different sections into which the exoplasm may be divided according to its relations to the central capsule and the calymma. In this respect the following parts may be generally distinguished--(1) the _Sarcomatrix_, or fundamental layer of the exoplasm, which surrounds the central capsule as a continuous sheath of sarcode and separates it from the calymma; (2) the _Sarcoplegma_, an irregular network of the exoplasm, which spreads throughout the gelatinous material of the calymma; (3) the _Sarcodictyum_ or network of sarcode on the outer surface of the calymma; and (4) the _Pseudopodia_, which project outwards from the latter and radiate into the water.