METABOLISM 273 



bundles of a needle-shaped alga intimately within the endoplasm ; 

 but on isolation the latter were always eventually ejected (Fig. 75). 

 The transient residents were apparently picked up from those 

 free-living in the culture jar. 



6. Parasites of stentor 



A natural transition leads from symbionts to parasites, though 

 their effects on the metabolism of stentors have not been explored. 

 For the following account I have relied in part upon Kirby's 

 (1941a, b) excellent reviews. 



Unidentified undulating filaments occurring in bundles within 

 vacuoles in the cytoplasm of stentors were observed by Miiller 

 (1856) and his students, two of whom considered these inhabitants 

 probably parasitic (Claparede and Lachmann, 1857). Balbiani 

 (1893) observed S. polymorphus with bloated nuclei in which the 

 macronucleus was parasitized and largely disintegrated by 

 ''Holospora". The host was otherwise normal but its ultimate 

 fate was not determined. Sphcerophrya stentoris Maupas is an 

 unstalked suctorian which is both free-living and parasitic on 

 species of Stentor. In its parasitic phase this organism lives in the 

 cytoplasm and is without tentacles or cilia. Kalmus (1928) reported 

 it in S. roeseli. Hetherington (1932b) reported a cytoplasmic 

 invasion by bacilli in S. coeruleiis. The infection caused the animals 

 to become pale, but they could be ''cured" by repeated transfers 

 to fresh medium. 



In S. coeruleiis and Spirostomum ambiguum^ Rowland (1928) 

 found an euglenoid with metabolic movements which appeared 

 commensal or endoparasitic. This she identified as Astasia captive 

 Beauchamp. The intruder restricted itself to the subpellicular 

 cortex. It was previously reported as an endoparasite in a rhabdo- 

 coele in France. Recently an apparently diflterent species of Astasia 

 has been described as a facultative parasite in S. coeruleus by 

 Schonfeld (1959). When well-fed stentors were presented with this 

 organism, grown separately in cultures, the stentors ate few and 

 digested those without ill effects. Starved animals gorged themselves 

 on the astasias, which were not digested but were liberated from 

 the food vacuoles and wandered about in the endoplasm. The 

 stentors eventually degenerated and died, a preceding vacuoliza- 

 tion possibly resulting from enlargement of the emptied food 



