6 



BRITISH FRESHWATER HELIOZOA. 



from the periphery of the clear zone, and appear to 

 be connected with the centriole by faint radiating 

 lines of minute granules the terminal ones of which 

 adjoining the axes of the pseudopodia may be 

 analogous to the blepharoplasts of Flagellates. 



During fission or budding accompanied by simple 

 division of the nucleus the central granule remains 

 unaffected, but during the process of karyokinesis it 

 divides and acts as a true centrosome. 



When buds are formed they at first contain a 

 nucleus only, which subsequently extrudes a centriole 

 to form the central granule. 



FIG. 179. Diagram of a Heliozoon with eccentric nucleus (Acanthovystis- 



type). (After Penarcl.) 



Except very rarely or in individuals of species 

 which possess unusually clear plasma, the central 

 granule is indistinguishable, being hidden by the 

 various inclusions, food-particles, etc., and a gentle 

 pressure on the animal is necessary to render it 

 visible : this is the best applied by allowing the water 

 under the cover glass to evaporate slowly. 



Although the central granule performs the functions 

 of a true centrosome it appears also to control the 

 emission and withdrawal of the pseudopodia ; it should 

 therefore be considered as analogous to, rather than 

 as homologous with, the centrosome of the metazoan 



