EADIOLAEIA.. 



189 



Order 3. RADIOLARIA.* 



Jfarine Rhizopoda with complicated differentiation of the sarcode 

 body, loith central capsule and radial silicious skeleton. 



The sarcode body contains a membranous porous capsule (the 

 central capsule), in which is contained a tough slimy protoplasm 

 with vacuoles and granules (intracapsular sarcode), fat and oil 

 globules, and albuminous bodies, and more rarely crystals and con- 

 cretions. The intracapsular mass contains also a single large nucleus 

 or several small nuclei. The sarcode which surrounds the capsule 

 and which emits on all sides simple or anastomosing pseudopodia, 

 contains numerous yellow cells, sometimes pigment masses ; and in 

 some cases delicate trans- 

 parent vesicles, or alveoli, 

 are found in the peripheral 

 layer between the radia- 

 ting pseudopodia (Thalas- 

 sicolla pelagica, fig. 129). 



Many Radio! aria form 

 colonies, and are composed 

 of numerous individual?. 

 [n such colonies the al- 

 veoli are placed in the 

 common protoplasm, 

 which contains in itself, 

 not as in the monozoic 

 Radiolaria a single cen- 

 tral capsule, but a number 

 of capsules. Only a few 



species remain naked and without firm deposits ; as a rule, the soft 

 body possesses a silicious skeleton, which either lies entirely outside 

 the central capsule (Ectolithia) or is partially within it (Entolithia). 

 In the most simple cases the skeleton consists of tanall, simple, or 

 toothed silicious needles (spicula) united together, which sometimes 

 give rise to a fine sponge work round the periphery of the proto- 

 plasm, e.fj., Physematium. In a higher grade we find stronger hollow 

 silicious spicules, which radiate from the middle point of the body 

 to the periphery in regular number and order, e.g., Acanthometra 



* Job. Miiller, " Ueber die Thalassicollen, Polycystinen und Acanthomctrcn," 

 Abh. tier Bcrl. ATtad. 1858. E. Haeckel, il Die Radiolarien," Eine Monographic 

 Berlin, 1802. 



FIG. 130. Acanthonxfra MilUeri (after B. Haeckel). 



