Reproduction and Life-Cycles 91 



— as reported in Paramecium (4, 30, 94, 123), Spatliidiiwi (253), Urolep- 

 tus (34), and Euplotes (149) — have not yet been correlated with the basic 

 concepts of mating types. Autogamy might bring about differentiation 

 within clones of Paramechim, but such an explanation is of uncertain 

 validity for other ciliates in which autogamy is unknown. 



Sexual maturity as a requirement for conjugation also was suggested 

 by Maupas, who believed that strains of ciliates are immature when first 

 established in cultures and must complete a certain number of genera- 

 tions before they can conjugate. In contrast to this view, conjugation has 

 occurred at intervals of only a few days in Paramecium aurelia (217) and 

 P. caudatum (4). Jennings (130) has suggested that the duration of "im- 

 maturity" in P. bursaria varies inversely with the food supply. 



Starvation is the third factor which Maupas considered essential. More 

 recently, conjugation of Paramecium multimicronucleatum (93), Spathi- 

 dium spathula (253) and Uroleptus mobilis (34), among others, has been 

 found to follow exhaustion of the food supply. On the other hand, con- 

 jugation has occurred in P. aurelia (123) just as a rich food supply was 

 beginning to decline, and also in P. caudatum (4), shortly before the pop- 

 ulations reached the maximum. The nature of the significant changes 

 which accompany or precede starvation is not yet known. However, the 

 physiological condition of individual ciliates seems to be an important 

 factor, since Boell and Woodruff (24) observed successful conjugation of 

 P. calkinsi only between ciliates with subnormal respiratory rates. A mat- 

 ing reaction between a normal ciliate and one with a low respiratory rate 

 sometimes occurred but conjugation was never completed. Ciliates with 

 high respiratory rates failed to show any mating reactions. 



Various environmental factors also have been correlated with conjuga- 

 tion. Darkness apparently favors and light suppresses conjugation in P. 

 aurelia (219), although light shows no comparable effect on P. caudatum 

 (97) or Euplotes patella (148). Temperature also influences conjugation, 

 and different optima have been noted for different varieties of P. aurelia 

 (223). In one variety the frequency of conjugation has ranged from zero 

 at 24.5° to 68 per cent at 17.6° (219). Conjugation in ConchopJtthirius 

 lamellidens, parasitic on the gills of a fresh-water mussel, has been ob- 

 served most frequently on the day following the new moon (208). Dilu- 

 tion of the medium with weak solutions of aluminum and iron chlorides 

 is said to have induced conjugation of Paramecium caudatum (258), but 

 Ball (4) obtained negative results with several clones of P. aurelia and 

 P. caudatum. One clone of P. caudatum did respond to such treatment 

 but distilled water was just as effective as the salt solutions. Conjugation 

 of Glaucoma scintillans has been stimulated by decreasing the salt con- 

 tent of the medium or increasing the concentration of glucose (43), and 

 also by adding pyruvic acid to the medium (45). 



The bacterial flora of cultures also may influence the incidence of con- 



