i8 



ZOOLOGY 



vacuole is formed. Encystment rarely takes place. Actinophrys 

 and another genus, Ehaphidiophrys^ have been observed to form 



Fig. 13. — Actinophrya sol, Ehrb. From Bronn. 



1. Nucleus in centre of body. 



2. Axis of pseudopodium extending into 



cell as far as nucleus. 



3. Contractile vacuole. 



4. A mass of food in a food vacuole. 



5. Superficial vacuolated protoplasm. 



6. Deep, finely granular protoplasm. 



colonies by incomplete fission. Eeproduction commonly takes 

 place by fission, but in some cases spores have been observed ; 

 those of Aetinosphaerium 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. 

 Bhaphidiqphrys is usually found in colonies ; it has a skeleton of 

 siliceous spicules, matted together round the body, each spicule 

 lying tangentiaUy to the surface. Acanthocystis has sihceous 

 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 Eadiolaria, Clathrulina (Fig. 15), 



