198 PROTOZOA 



rate and technical procedures: obtaining conjugants, following 

 the life cycle, genetic studies, serological procedures, and other 

 physiological procedures. These are totally unsuitable for use 

 in routine identification. Mean body length alone, among all the 

 traits listed, could be used routinely. And this does not identify 

 all the varieties; it could only limit an unknown to one of three 

 or four groups of varieties. I therefore also reject combinations 

 of the traits in Table III as a basis for assigning species names 

 to the varieties. 



Nevertheless, the information summarized in Tables I, II, and 

 III make it possible to define the varieties and to prescribe a pro- 

 cedure for identifying them without recourse to living standard 

 cultures. Sonneborn (1950) explained this in detail for the 8 

 varieties known at that time. The same general approach, sup- 

 plemented by much new information, would make possible 

 identification of all 16 varieties now known. The first step would 

 be to obtain many strains from regions that have provided the 

 known varieties. From each strain mating types would have to 

 be isolated and, in the way originally done, the various strains 

 would have to be sorted into varieties. When 16 have been ob- 

 tained, they could be identified with the 16 now known in the 

 following ways. The only variety with 4 mating types would 

 be variety 16. 3 Varieties 2, 3, 11, and 15 could be identified by 

 their distinctive diurnal periods of sexual reactivity and their 

 sizes. The remaining large animal varieties would be 12 and 13. 

 Variety 12 2 could be identified as the only large variety that regu- 

 larly formed 2 macronuclear anlagen and 2 micronuclei after 

 fertilization. Variety 13 could be identified by its regular selfing. 6 

 Of the 4 smallest animal varieties (4, 8, 10, and 14), 8 could be 

 singled out because of the reaction of one of its mating types 

 with one of those of the already identified variety 3. Variety 4 

 would then be identifiable by its two-way sexual reactions with 

 variety 8. The remaining two varieties ( 10 and 14 ) have been but 

 recently discovered and I do not yet know enough about them to 

 prescribe how to differentiate them. The system of reactions in 

 Table I shows how variety 3 could be used to identify varieties 



