SUN-ANIMALCULE 



113 



bottom. It is spherical and minute, measuring at most 

 0-05 mm. in diameter. Long stiff pseudopodia radiate 

 out from the body. A clear axial filament runs up each 

 pseudopodium, and the small organisms on which Actino- 

 phrys feeds are paralysed when they come in contact with 

 the pseudopodia. 



The body consists of ectoplasm and endoplasm. The 

 ectoplasm is a thick external layer closely packed with 

 large vacuoles, which are non-contractile and contain a 

 clear fluid. But food vacuoles are formed as in other 



Fig. 47. — Actinophrys sol (Sun-animalcule). 

 — After Grenacher. 



»., Nucleus ; f.v., food vacuole ; v., contractile vacuole ; ps., pseudopodium. 



Protozoa, and there is also a single contractile vacuole. 

 The endoplasm forms the central mass. It is not vacuo- 

 lated, and contains the large, centrally placed nucleus. 



Life-history. — An Actinophrys may withdraw its 

 pseudopodia and divide into two,^ with or without the 

 formation of a cyst. A number of individuals may unite 

 for a time by the ectoplasm alone, and separate without 

 any nuclear fusion having taken place (plastogamy). 

 But Schaudinn has described a true sexual process which 

 offers an interesting analogy to the processes of maturation 

 and fertilisation in the higher animals. 



A number of individuals become joined up in a common 



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