SPECIES OF STENTOR 335 



transferred to a different genus and a few new ones have been 

 added. Stentors are perhaps most easily confused with unstalked 

 vorticellids, but the latter have ciliary rows which are transverse 

 rather than longitudinal and the oral band spirals in the opposite 

 direction. 



A key to the species and guide to synonomy was provided by 

 Kahl. Drawing on the available literature and mindful that I have 

 not seen every one of the species, I shall attempt to give a brief but 

 distinguishing description of each, illustrated by the frontispiece 

 and Fig. 95. For all its variability, size is still a useful criterion. 

 Approximate average diameters of contracted animals are given, 

 because the degree of extension is variable and samples to be 

 examined are generally not in repose. New species have been 

 described from a single specimen but this is certainly to be 

 frowned upon, because stentors can easily be injured when pipetted 

 with filamentous algae and may retain abnormal or incompleted 

 shapes for some time. Moreover, in the method of cell fusion by 

 grafting we now have a new means for testing species differences. 

 When diverse forms are combined in about equal proportions they 

 appear as if stricken and do not produce viable clones as do fusion 

 complexes of like species. 



The following species have blue to greenish or violet pigment 

 granules : 



S. coeruleus Ehrenberg 1830. This is the large, cerulean blue 

 species, largest (350/x) of all the stentors, with a moniliform 

 macronucleus. 



S. loricata Bary 1950. The only large, self-pigmented green 

 stentor which builds a case or lorica. The macronucleus is vermi- 

 form. So far reported only from a stream in New Zealand. 



S. multiformis Miiller 1786. This is a tiny (95 /x) blue-green 

 stentor with an oval macronucleus. (A few further comments are 

 apropos. When swimming, these stentors often appear plump, with 

 rounded posterior ends. They have few — approximately 25 — 

 pigment stripes which are therefore relatively large. Kahl states 

 that typically there is but one micronucleus. I have found some 

 collections with symbiotic chlorellae. This species is reported from 

 brackish or salt water, but I have repeatedly found animals corres- 

 ponding to its description in fresh water. The fresh water form 



