18 ZOOLOGY 
vacuole is formed. Encystment rarely takes place. Actinophrys 
and another genus, Lhaphidiophrys, have been observed to form 
Fic. 13.—Actinophrys sol, Ehrb. From Bronn. 
1. Nucleus in centre of body. 4. A mass of food in a food vacuole. 
2. Axis of pseudopodium extending into 5. Superficial vacuolated protoplasm. 
cell as far as nucleus. 6. Deep, finely granular protoplasm. 
3. Contractile vacuole. 
colonies by incomplete fission. Reproduction commonly takes 
place by fission, but in some cases spores have been observed ; 
those of Actinosphaertum being provided with a siliceous shell. 
This last-named genus (Fig. 14) is much larger than Actino- 
phrys; it contains numerous nuclei, situated in the deeper 
protoplasm. The pseudopodia are supported by an axial ray. 
Rhaphidiophrys is usually found in colonies ; it has a skeleton of 
siliceous spicules, matted together round the body, each spicule 
lying tangentially to the surface. Acanthocystis has siliceous 
rays arranged radially ; they are of two kinds: short ones, which 
are forked at their outer end, and long stout ones. They are 
attached to the body by a small disk. Finally, leading on to 
the condition found in the Radiolaria, Clathrulina (Fig. 15), 
