HELIOZOA. 871 



Encystation occurs, in some instances preceding reproduction, in 

 others of unascertained significance. Actinophrys secretes a gelatinous 

 capsule and retracts the pseudopodia, whilst the vacuoles disappear. The 

 inner part only (?) of the protoplasm divides, and each part forms a double 

 cyst ; the outer cyst ruptures, the inner with its contents escapes ; the con- 

 tained mass shows a separation of ecto- and endo-sarc, developes a contrac- 

 tile vacuole and pseudopodia, by which the inner cyst is pierced and dis- 

 solved (Cienkowski). Or there is a double cyst, within which the animal may 

 or may not divide ; a contractile vacuole persists ; both cysts are ruptured 

 to give exit to the contents (Lieberkuhn). In Actinosphaerium the radiant 

 pseudopodia are withdrawn, but branched pseudopodia of varying length 

 are thrown out and the animal creeps about for twenty-four hours. A 

 thick gelatinous coat is then formed, the vacuoles disappear, and the nuclei 

 are said to diminish in number (Schulze, Brandt). The protoplasm next 

 divides into 2-35 portions successively (Schulze, Green ), or simultaneously 

 (Brandt). Each portion is uni-nucleate, or else becomes so (Schneider), 

 and surrounds itself with a siliceous cyst (Schulze). Or they fuse in 

 pairs so as to reduce the number present by one half, with or without 

 an odd member (Greeff) ; or again, each part forms a thin membranous 

 cyst, divides into two within it, the two parts subsequently fusing and the 

 cyst disappearing (Brandt). Ultimately a siliceous cyst is formed, con- 

 tinuous or of small pieces (Schneider, Brandt), single, or double (Greeff). 

 The young Actinosphaerium escapes in spring, and is uni-nucleate (Schulze) 

 or multi-nucleate (Schneider, Brandt). When Clathrulina encysts it con- 

 tracts and developes a spinose siliceous envelope ; or it divides previously 

 into two or more portions, each of which then forms a separate and similar 

 envelope. Actinolophus surrounds itself with a gelatinous coat, on the 

 outer surface of which appears a layer of loosely arranged hexagonal 

 siliceous plates. The pseudopodia are retracted, their axial filaments and 

 central granule disappear, whilst the nucleus divides into two. Further 

 changes have not been witnessed. The contraction of the body into a 

 small sphere, the formation of a thin or thick envelope round it, or of 

 a siliceous cyst (Pompholyxophrys^ Acanthocystis turfacea s. viridis)^ has 

 been recorded in several genera. 



The Heliozoa are a class widely distributed over the world. The 

 greater number of genera are freshwater and are found especially in peat 



spores (SB. Niederrhein. Ges. in Bonn, 1871). Foulke states that a Clathrulina became filled with 

 green particles actively motile, which were expelled, a number together, in a thin sac; by the 

 bursting of the latter they were set free, but were not traced further (A. N. H. (5), xiv. p. 269). It 

 is probable that these and similar observations refer to parasitic organisms. Brandt indeed has con- ! 

 firmed Greeff (supra), but has seen the organisms in large numbers within the food vacuoles, and 

 their multiplication when expelled from the body. He refers them to a parasite akin to the fungus 

 Pythium (Monatsb. k. Acad. Berlin, 1881, p. 399). Foulke has described the ejectment of 

 globules from two fused Actinosphaeria which eventually developed into the parent form (A. N. H. 

 (5), xii. p. 206). 



