PARAMECIUM 77 



November 1, 1939, the culture had attained the number of about 20,000 

 generations. The significance may be in the determining of inheritance. 

 The scrapping of the old macronucleus and the development of a new one 

 from the fusion micronucleus suggest the need of harmonious direction 

 of activities in an animal differing from the conjugant parent by nuclear 

 material received from the other conjugant. 



106. Endomixis. — An interesting phenomenon analogous to conjuga- 

 tion, but taking place within a single individual, has been observed 

 in Paramecium aurelia Mliller (Fig. 28). This species possesses two 

 micronuclei, exhibits a definite rhythm in the rate of division, and periodi- 

 cally undergoes what has been called endomixis. During the process 

 the macronucleus breaks down and disappears and the micronuclei 

 undergo two divisions, producing altogether eight micronuclei. Six 

 of these disintegrate and disappear. The Paramecium then divides and 

 each of the offspring receives one micronucleus. This micronucleus 

 divides into two and these divide again, producing four. Two of these 

 develop into macronuclei and two remain micronuclei. The mic- 

 ronuclei divide again and the entire animal divides, resulting in 

 two, each with two micronuclei and one macronucleus. Four individuals 

 have thus been produced. This process also occurs in Paramecium 

 caudatum and in other forms. The result of endomixis may be the same 

 as that of conjugation. 



