320 THE BIOLOGY OF STENTOR 



2. Racial differences 



In the best known species, coeruleus^ definable differences between 

 various stocks and clones may turn out to be inherited racial 

 differences because they have appeared and persisted in strains 

 cultured by uniform methods. Since we still lack the means for 

 inducing conjugation at will in stentors, the most fruitful approach 

 would be by nuclear exchanges to test whether these traits are 

 determined by the nucleus or the cytoplasm. In one instance this 

 has been done, but for the most part we can at present merely 

 describe possible strain differences which might be analyzed in 

 this way. 



State of the endoplasm. Separate clones of coeruleus may differ 

 in regard to the transparency of the endoplasm, a difference which 

 manifests itself very clearly in the ease with which macronuclear 

 nodes can be made out in enucleation experiments. The two 

 extremes of this condition are shown in my stock from Urbana, 

 Illinois, in which the cytoplasm is consistently transparent so that 

 the nucleus is clearly visible except in over-fed animals, and 

 another from Stella, Washington, in which the endoplasm is 

 notably opaque, except when the animals have been completely 

 starved, and this stock has also remained consistently so 

 characterized for 4 years. 



Size. If the Stentor *'X" mentioned in the preceding section 

 was indeed a race of coeruleus^ then we had a dwarf variety in which 

 the cells never attained a volume larger than about i/8th that of 

 most stocks of this species. Other stocks of coeruleus seem to show 

 much less striking differences in the maximum size attained, but 

 careful measurements might reveal consistent size differences such 

 as have already been found in other genera of ciliates, notably 

 Paramecium. 



^^ Astomatous". A stock of coeruleus obtained from Woods Hole 

 Biological Supply in 1950 was unique in producing some indivi- 

 duals temporarily without mouthparts (Tartar, 1957b). After 

 growing these organisms in the laboratory for 4 years it was noticed 

 that in certain subcultures about i % of the stentors were poorly 

 fed because they lacked ingestive organelles. In division, reorgani- 

 zation, and regeneration the oral primordium developed without 

 its posterior end invaginating and forming a gullet, and the oral 

 pouch was generally missing. The membranellar band itself 



