REPRODUCTION 157 



was pointed out by Jennings, the mating types may be of general oc- 

 currence among ciliates; for example, Maupas (1889) observed that 

 in Lionotus {Loxophyllum) fasciola, Leucophrys patula, Siylonychia 

 pustulata, and Onychodromus graridis, conjugation took place be- 

 tween the members of two clones of different origin, and not among 

 the members of a single clone. Precise information on the occurrence 

 among different ciliates depends on future research. 



In Paramecium aurelia, Sonneborn distinguishes seven varieties 

 which possess the same morphological characteristics. There occurs 

 no conjugation between the clones of different varieties. Within 

 each of the six varieties, there are two mating types, while there is 

 only one type in the seventh variety. Animals belonging to the 

 same variety, but to different mating types only conjugate when 

 put together (Table 6). In P. hursaria, Jennings (1938, 1939) finds 

 three varieties, but each of two varieties contains four mating types 

 and in the third variety eight mating types occur (Table 6). In 

 Euplotes patella, Kimball (1939) observed six mating types (Table 

 6). These mating types cannot be considered as the true sex types, 

 since the conjugants mutually fertilize each other. 



Recent studies of mating types have revealed much information 

 regarding 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. hursaria, 

 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. Pre- 



