92 Reproduction and Life-Cycles 



jugation. Chatton and Chatton (44) found that Glaucoma scintillans 

 conjugated when fed on Escherichia coli, Proteus vulgaris, Shigella dysen- 

 teriae, or Staphylococcus aureus, but not on Pseiidomonas aeruginosa, P. 

 fluorescens or any one of several other bacterial species. Conjugation of 

 P. caudatum was observed in cultures containing only a gram-negative 

 bacillus, but not in other cultures containing at least three kinds of bac- 

 teria (46). Accordingly, it was suggested that so-called conjugating and 

 non-conjugating races of ciliates may be determined by the bacterial flora. 

 This conclusion was not supported by Sonneborn and Cohen (222) who 

 induced conjugation invariably in a Johns Hopkins strain and never in 

 Woodruff's strain of P. aurelia when both strains were maintained on the 

 same bacterial types. 



Mating types in ciliates^ 



Following the observations of Sonneborn (218, 219) on Para- 

 mecium aurelia, P. calkinsi, and P. trichium and those of Jennings (124, 

 125) on P. bursaria, mating types have been demonstrated also in P. 

 caudatum (95, 96, 97, 98, 98a), P. midtimicronucleatum (94, 95), and 

 Euplotes patella (148,149). 



The situation in P. bursaria may be illustrated as follows. Two strains, 

 A and B, have been established in pure lines. Conjugation does not occur 

 among ciliates of strain A or among those of strain B, although mixtures 

 of the two do show conjugation. Therefore strains A and B seem to be- 

 long to different sexes. A third strain, C, tested in the same way with 

 strain A, behaves like strain B, and consequently might be expected to 

 have the same sex. However, conjugation occurs also in mixtures with 

 strains B and C. A fourth strain, D, is found to conjugate with any of the 

 other three. At this point, conjugation in P. bursaria begins to strain 

 basic concepts of bisexuality in animals, and confusion in terminology 

 has been avoided by the substitution of "mating type" for "sex." Further 

 investigation has demonstrated additional groups of mating types. A 

 second group, or variety, contains eight mating types (E, F, G, H, J, K, 

 L, M) which will not conjugate with the four types (A-D) in variety I. 

 Mating types N, O, P, and O have been assigned to a third variety, since 

 they will not conjugate with types belonging to varieties I and II. Variety 

 IV contains types R and S, which do not mate with members of varieties 

 I, II or III. Variety V is represented by mating type T, composed of 

 strains obtained from Russia, and will not mate with members of the 

 other varieties (132). A more recently recognized variety VI, including 

 strains from Czechoslovakia, England and Ireland, contains mating types 

 U, V, W and X (55). 



In Paramecium aurelia seven varieties have been recognized (224). 

 Six of these contain two mating types, and one type has been assigned to 



^This subject has been reviewed by Kimball (150). 



