CLASSIFICA TION OF PROTOZOA. 1 1 j 



nuclei embedded in it, serves for the formation of flagellate spores The 

 extra-capsular portion is partly the general 'organ' for intercourse with 

 the outer world, partly the special 'organ' of protection and nutrition 

 Ihe skeleton (usually present) varies in form, and is generally composed 

 of sihca arranged m one of sixteen or twenty geometrical forms, some- 

 times of a horn-hke substance called acanthin. The cell usually leads 

 an isolated existence (Monocyttaria) ; only a few form colonies of cells 

 {Polycyttaria)." (With .u few verbal changes, from Hjeckel's "Chal- 

 lenger" Report, 1887.) 



Most Radiolarians include unicellular plants, with which they live in 

 intimate mutual partnership (symbiosis). Division is probably the 

 commonest mode of multiplication, but flagellate spores— sometimes 

 of two sizes, small and large, as if male and female — have also been 

 observed. Their conjugation is still unknown. Lankester notes that the 

 central capsule of a Radiolarian may be compared with the buried 

 shell of Hasiigerina, 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 oore of the great depths, and occur 

 abundantly as fossils from Palaeozoic times. 



The general classification is based on the chemical nature of the 

 skeleton (flint or acanthin), and on the nature of the ojjenings in the 

 central capsule. 



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

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

 Eucyrtidium (flinty skeleton, vrith one perforate area in cone-shaped 

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

 than one perforate area) ; Collosoum and Sphcerozouvi, multicellular 



colonial forms. 



C. — Predominantly Encysted Forms. 



8. Gregarinida (or better, perhaps, Sporozoa). — Protozoa ot 

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

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

 of animals ; often, especially when young, within the cells of their host ; 

 deriving their food by absorbing difiusible juices. A single large nucleus ; 

 no contractile vacuole. Reproduction by division in early life, but 

 typically by spore-formation. An encysted phase precedes the division 

 into encased spores. The young forms escaping from a spore-case may 

 be flagellate or amoeboid ; but, except in a very few cases, passivity pre- 

 vails, and the adults are much restricted in their contractile movements. 

 Conjugation, followed by fusion, often precedes encystation ; and in- 

 dependently of the latter two forms often occur associated but not 

 fiised. 



Examples. — Monocystis, in earthworm ; Gregarina, with a cross par- 

 tition, in food-canal of Arthropods ; Eimeria, remaining, except in young 

 stages, within a cell of the host ; Drepanidiwn, and other forms, in blood 

 corpuscles ; Afyxidium, with amoeboid adult ; Sarcocystis, in muscle 

 fibres of Mammals and some other Vertebrates. 



