THE HELIOZOA 



21 



of the cell-body and of the cyst-wall. On emerging from the cyst, 

 after division, vacuoles and pseudopodia are developed, and the 

 adult condition is assumed. 



The majority of the higher Heliozoa resemble Actinophrys in 

 general structure, though their appearance may be greatly altered 

 by the presence of a skeleton or by the formation of a stalk. 



The modifications of the cell-body are chiefly those connected with 

 the greater or less development of vacuoles and of various coloured 

 substances. The division into ectoplasm and endoplasm is generally 

 obvious. The ectoplasm usually contains contractile vacuoles, which 



Fio. 3. 



Actinophrys sol. I, two free-swimming individuals in conjugation. II, the same individuals 

 in an early phase of encystment. The nuclei are considerably enlarged. Ill, formation of 

 the polar spindles. IV, stage with two reduced nuclei and degenerating polar nuclei. V, 

 the reduced nuclei have fused together and the polar nuclei have reached the periphery. 

 VI, the first segmentation spindle is formed and the polar nuclei are ejected as polar bodies. 

 cr, cyst membrane ; c.v, contractile vacuoles ; N, nuclei ; P.N, polar nuclei ; P.B, polar 

 bodies ; P.Sp, polar spindle ; S.Sp, segmentation spindle. (After Schaudinn.) 



may be very numerous (more than 20 in Acanthocystis). In 

 Actinosphaerium the system of non-contractile vacuoles is even more 

 highly developed than in Actinophrys, but in the skeletogenous genera 

 the non-contractile vacuoles are few. The ectoplasm is usually the 

 seat of digestion and assimilation, as it is in Actinoplirys ; and usually 

 contains refringent granules, which may be rounded, like those of 

 Actinophrys, or crystalloid (Heteropkrys). Perhaps the larger coloured 

 granules which occur either in the ectoplasm or in the endoplasm, or 

 scattered throughout the body, belong to a different category from 

 the refringent granules ; large brown granules may occur in the 

 ectoplasm (Pinacocystis), brownish or yellowish bodies may be scattered 



