PARAMECIUM: CONJUGATION 



55 



conjugation, but in a single individual. The meganucleus dis- 

 appears, the micronucleus divides a number of times, and new 

 individuals, with new nuclear outfits, are formed by fission. 

 According to some workers the last surviving pair of micronuclei 

 immediately fuse with each other. If this is so, the process is one 

 of autogamy, or the fusion of gametes derived from a single 

 parent. Endomixis seems to have some of the same good effect 

 on a culture as does conjugation. In P. aiirelia the two processes 

 alternate. 



Laboratory stocks of Paramecium often show a condition called 



---jmeg 



TTLL 



Fig. 29. — Semidiagrammatic views of individuals of 

 Paramecium caudatum. 



Ay In depression ; B, in conjugation ; C, in fission. 

 g.. Gullet ; tneg., meganucleus ; mi., micronucleus. 



depression (Fig. 29/I). The meganucleus is enlarged and there 

 are changes in the shape of the body, and death follows. Various 

 changes in the environment can alleviate depression, and 

 it is probable that the cause lies in unnatural conditions of 

 culture. 



Genetical experiments have shown that the characters of an 

 individual Paramecium are determined by its meganucleus, and 

 this is in agreement with the fact that ciliates without micronuclei 

 can carry out all functions except those of conjugation and 

 endomixis, while loss of the meganucleus leads to death within 

 two days. It is obvious that transmission of hereditary characters 

 can take place onty through the micronucleus, since the other is 

 destroyed. 



