86 PROTOZOA 



endoplasni : the nucleus first undergoes lirood division, and the 

 plasma within the capsule Ijeconies concentrated about its 

 offspring, and segregates into the spores : the extracapsular 

 plasm disintegrates.^ 



The Yellow Cells {Zooxanthella), so frequently found in the 

 Eadiolaria were long thought to be constituents of their body. 

 Cieukowsky found that when the host died from being kept in 

 unchanged water, the yellow cells survived and nmltiplied freely, 

 often escaping from the gelatinised cell-wall as bitiagellate zoospores. 

 The cell-wall is of cellulose. The cell contains two chloroplastids, 

 or plates coloured with the vegetal pigment " diatomin." Besides 

 ordinary transverse fission in the ordinary encysted state in the 

 ectoplasm of the host, when free they may pass into what is 

 known as a " Fabnella-state," the cell-walls gelatinising ; in this 

 condition they multiply freely, and constitute a jelly in which the 

 individual cells are seen as rounded bodies. They contain starch 

 in two forms — large hollow granules, not doubly refractive, and 

 small solid granules which polarise light. We may regard them 

 as Chrysomonadaceae (p. 113). Similar organisms occur in many 

 Anthozoa (see pp. 261, 339, 373 f, 396). Diatomaceae (yellow- 

 Algae with silicified cell-walls) sometimes live in the jelly of 

 certain Collosijhaera. Both these forms live in the state known 

 as " symbiosis " with their host ; i.e. they are in mutually helpful 

 association, the Eadiolarian absorbing salts from the water for 

 the nutrition of both, and the Alga or Flagellate taking up the 

 COg due to the respiration of the host, and building up organic 

 material, the surplus of which is doubtless utilised, at least in 

 part, for the niitrition of the host. A similar union l)etween a 

 Fungus and a coloured vegetal (" holophytic ") organism is 

 known as a Lichen. 



The Suctorian Infusorian Amochoj'hri/a is parasitic in the 

 ectoplasm of certain Acantharia, and in the peculiar genus Sticho- 

 lonche which appears to be intermediate between this group and 

 Heliozoa. 



The Silicoliagellate family Dictyochidae are found temporarily 



' Porta has described reproduction by spores and by budding in Acantharia, 

 Iie7id. H. 1st. Lomb. xxxiv. 1901 (ex Journ. Ji. Micr. Soc. 1903, p. 45). In 

 Thalasso2)hysa and its allies zoospore reproduction appears to be rejtlaced by a 

 process in which the central capsule loses its membrane, elongates, becomes 

 niultinuclear, and ultimately breaks up into the nucleate portions, each annexing 

 an envelope of ectoplasm to become a new individual (see Arch. Prof., vol. i. 1902). 



