19G PROTOZOOLOGY 



seemingly normal during the first 16 hours, become abnormal sud- 

 denly after that time, and the micronuclei divide only once and there 

 is no nuclear exchange. The death of conjugants or exconjugants is 

 possibly due to physiological incompatibility between the varieties 

 upon coming in contact or probably due to "something that diffuses 

 from one conjugant to the other." 



Studies of mating types have revealed much information re- 

 garding conjugation. Conjugation usually does not occur in well-fed 

 or extremely starved animals, and appears to take place shortly 

 after the depletion of food. Temperature also plays a role in con- 

 jugation, as it takes place within a certain range of temperature 

 which varies even in a single species among different varieties 

 (Sonneborn). Light seems to have different effects on conjugation 

 in different varieties of P. aurelia. The time between two conju- 

 gations also varies in different species and varieties. In P. bursaria, 

 Jennings found that in some races the second conjugation would 

 not take place for many months after the first, while in others 

 such an "immature" period may be only a few weeks. In P. aurelia, 

 in some varieties there is no "immature" period, while in others there 

 is 6 to 10 days' "immaturity." 



Very little is known about the physiological state of conjugants 

 as compared with vegetative individuals. Several investigators ob- 

 served that animals which participate in conjugation show much 

 viscous body surface. Boell and Woodruff (1941) found that the 

 mating individuals of Paramecium calkinsi show a lower respiratory 

 rate than not-mating individuals. Neither is the mechanism of con- 

 jugation understood at present. Kimball (1942) discovered in 

 Euplotes patella, the fluid taken from cultures of animals of one type 

 induces conjugation among the animals of other types (p. 235). Pre- 

 sumably certain substances are secreted by the organisms and be- 

 come diffused in the culture fluid. In Paramecium aurelia, Sonne- 

 born (1943) found that of the four races of variety 4, race 51 was a 

 "killer," while the other three races, "sensitive." Fluid in which the 

 killer race grew, kills the individuals of the sensitive races. As has 

 been mentioned already, P. bursaria designated as type T (variety 

 5) (Table 7) conjugates with none. But Chen (1945) found that its 

 culture fluid induces conjugation among a small number of the indi- 

 viduals of one mating type of varieties 2, 3, 4 and 6, in which nuclear 

 changes proceed as in normal conjugation. Furthermore, this fluid 

 is capable of inducing autogamy in single animals. Other visible in- 

 fluences of the fluid on organisms are sluggishness of movement and 

 darker coloration and distortion of the body. 



