SYSTEMATIC SURVEY. 103 



also. Most lead an isolated existence (Monocyttaria) ; a few form 

 colonies by fusion [Polycyttaria). 



Most Radiolarians include unicellular Algfe (yellow cells), with which 

 they live in intimate mutual partnership (symbiosis). Division is pro- 

 bably the commonest mode of multiplication, but flagellate spores — 

 sometimes of two sizes, small and large, as if male and female — may be 

 formed in the central capsule. Conjugation is still unknown. Professor 

 Lankester notes that the central capsule of a Radiolarian may be com- 

 pared with the enclosed shell oi ITastigsrzna^ and that the character of the 

 protoplasm, which in contrast with that of Foraminifera is abundantly 

 vacuolated, may be associated with the pelagic life, which is rare in the 

 former class. Radiolarians form much of the ooze of the great depths, 

 and occur abundantly as fossils from Palxozoic times. 



Examples. — Thalassicola (no skeleton); Acanthometra (acanthin) ; 

 Adinomma (flinty skeleton, central capsule with pores all over) ; 



Y\v,. 29. — Optical section of a Radiolarian (Actinomma). 

 (After H/ECKEL. ) 



a. Nucleus; /;. Wall of central capsule ; c. Siliceous shell within 

 nucleus ; cl. Middle shell within central capsule ; A Outer shell in 

 extra-capsular substance. Four radial spicules hold the three 

 spherical shells together. 



Eucyrtiduim (flinty skeleton, with one perforate area in cone shaped 

 central capsule) ; Atihsplucra (flinty skeleton, central capsule with more 

 than one perforate area) ; CoUozouin and Splurrozoiini, multicellular 

 colonial forms. 



C. — Predoininantly Encysted Protozoa — Sporozoa. 



8. Gregarinida (or better, perhaps, SrOROZOA). — Protozoa^ of 

 parasitic habit, very passive in adult life, clothed by a definite rind, 

 almost never with any locomotor processes. Found in almost all kinds 



