EEPORT ON THE RADIOLARIA. lix 



of this there is no doubt that all Xanthellfe (the Zooxanthclla cxtracapsularis of Spumellakia and 

 Nassellaeia, and the Zooxantlidla infracapsularis of the Acantharia, and possibly also the 

 Zooxanthclla pliwodaris of the Ph^odaeia) do not originally belong to the Eadiolarian organism, as 

 was believed up to the time of Cienkowski, but penetrate actively into it from without, or are 

 taken in passively by means of the pseudopodia. In any case their symbiosis, when they are 

 associated with the Eadiolarian cell in large numbers, may be of great advantage to both parties, 

 since the metastasis of the Xanthella is vegetable, that of the Eadiolarian animal in character. In 

 any case their symbiosis is to a large extent accidental, by no means as necessary as in the case of 

 the Lichens. See on these points in addition to Brandt and Geddes {loc. cit.) also Geza Enz, Das 

 Consortial-Verhiiltniss von Algeu uud Thieren, Biol. Centralbl., Bd. ii. No. 15, 1883, Oskar Hertwig, 

 Die Symbiose oder das Genossenschaft.sleben im Thierreich, Jena, 1883, and Blitschli, Die 

 Eadiolarien, in Broun's Klass. u. Ord. d. Thierreichs, 1882 (L. N. 41, pp. 456-462). 



91. TJie 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 impoitant 

 constituent of the extracapsulum, besides the calymma. Although the extracapsular 

 and intracapsular protoplasm of the Eadiolaria are everywhere in direct communi- 

 cation, 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, pro- 

 ducing 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 

 Sarcodictyuin or network of sarcode on the outer surface of the calymma ; and (4) the 

 Pseudopiodia, which project outwards from the latter and radiate into the water. 



92. The Sarcomatrix. — The sarcomatrix, being " the fundamental layer of the 

 pseudopodia " (or " matrix of the exoplasm "), constitutes the proximal innermost section 

 of the extracapsular sarcode, and in all Radiolaria forms a thin continuous mucous 

 layer, which covers the whole outer surface of the central capsule and separates it from 

 the surrounding calymma (see note A, below). The sarcomatrix communicates internally 



