976 PROTOZOA 



peatedly within single clones. Second, viable inbred progeny 

 were obtained in the laboratory. Although as mentioned, mortal- 

 ity was high among the inbred progeny of the two original iso- 

 lates, Kimball and Powers were able to pursue genetic analysis 

 with them. Whether it was possible to select in this way com- 

 binations relatively free from further inbreeding mortality is not 

 ascertainable from their papers, so far as I can discover. It is also 

 not clear whether continued inbreeding led to progressive de- 

 terioration, but Kimball eventually abandoned the organism be- 

 cause of difficulties in maintaining cultures. Either inbreeding 

 degeneration or aging or both may have played a part in this. To 

 the extent that inbreeding yields viable progeny and to the extent 

 that selfing occurs in nature, E. patella may be considered as a 

 facultative or potential inbreeder, although provided with life 

 features that make outbreeding the usual practice. Here, as in 

 Tetrahymena, we may see traces of how an organism which is 

 customarily an outbreeder contains the seeds of an inbreeding 

 evolutionary descendant. 



Other Ciliates 



Mating types and something about the breeding system are 

 known for relatively few Ciliates other than those already dealt 

 with. All can be quickly dealt with except Oxytricha bifaria about 

 which much of interest is known. A system of three mating types 

 which show the P. bursaria relations (each type mating with 

 both of the others) was found by Sonneborn (1938, 1939) in 

 P. trichium. Diller (1948) and Wichterman (1937) have found 

 strains of P. trichium which self very readily. 1 have also en- 

 countered such strains. On the other hand, those in which I re- 

 ported the three mating types did not self, and Wichterman 

 I 1953) has had one strain under cultivation for twelve years 

 without finding selfing. Whether the selfing and nonselfing strains 

 belong to different varieties is unknown. If they do, the former 

 would probably be found to be an inbreeder, the latter an out- 

 breeder. Sonneborn (1938) reported a pair of mating types in 

 P. calkinsi. Wichterman (1950, 1951) found a second variety 

 which also contained two mating types. I have found multiple 



