7o MANUAL OF ZOOLOGY. 



which cannot be regarded as typical members of the order 

 no contractile vesicle is present. In the aberrant Myxobrachia, 

 also, the characteristic radiating pseudopodia are absent, the 

 organism being furnished with from one to sixteen arm-like 

 processes of sarcode, the clavate ends of which enclose nu- 

 merous calcareous bodies (coccoliths and coccospheres), which 

 may, however, be simply taken in as food. 



The protoplasm of the body of a Radiolarian consists typi- 

 cally of a central and a peripheral portion, of which the former 

 is enclosed in a porous, membranous, or chitinous capsule, 

 while the latter is surrounded by a gelatinous investment. In 

 the often brightly coloured extra- capsular sarcode are scattered 

 the yellow cells above alluded to, which some regard as being 

 truly of a parasitic nature. The pseudopodia (fig. 17), are 

 numerous, filamentous, radiately disposed, and sometimes 

 anastomosing. Skeletal structures, in the form of spicular, 

 radiating spines, or fenestrated shells, may be developed in 



Fig. T-T.Eucecryphalus Schultzei. with the pseudopoilia extended, showing the per- 

 ' - J ' ' ,.,,,', . '^ mic body . After Kolliker. (The r"* u " 



ivart for the use of this engraving.) 



forated siliceous test and the lobed protoplasmic body. After Kolliker. (The author 

 is indebted to the kindness of Professor Mi\ 



either the extra- capsular or the intra-capsular sarcode, or in 

 both. These skeletal structures may be wanting ; but, when 

 present, they are almost always siliceous, rarely horny, never 

 calcareous. The animal is usually simple, varying in size from 

 T^ir to -sV inch, or rarely more, but in other cases ( Collosoum) 

 colonies are formed, which may reach two inches in diameter. 

 Reproduction is often by fission ; but in other cases the intra- 

 capsular sarcode breaks up into minute germs or zoospores, 

 each of which possesses a nucleus and a flagellum. 



