INHERITANCE 



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1. The macronucleus or macronuclei of each individual disappear, 

 being absorbed into the cytoplasm. 



2. If more than one micronucleus are present, usually all but one are 

 absorbed and disappear. 



3. The single micronucleus divides three times in succession (the 

 "maturation divisions"). By the first two divisions (Fig. 174, 1 and 2) 

 four nuclei are produced; of these, three are absorbed and disappear. 

 The remaining one divides once more into two (Fig. 174, at 3). 



Figure 174. The three maturation divisions (1, 2, 3) and the exchange of pronuclei 

 in the micronuclei during conjugation. A and D are the micronuclei of the two con- 

 jugants respectively. Reduction at the second division, represented by the separation of 

 XX and XY. The diagram illustrates the fact that the two diploid nuclei produced 

 (above) are alike in constitution. 



4. The two nuclei produced by the third division are haploid, so that 

 one of the three maturation divisions is a reduction division. 



5. One of the two haploid nuclei (the "migrating pronucleus") in 

 each individual passes over into the other individual, where it unites 

 with the remaining one ("stationary pronucleus") of that individual. 

 Thus there is produced again a diploid nucleus in each individual. 



6. This diploid nucleus divides, some of its products becoming large 

 as macronuclei, others remaining small as micronuclei. These macro- 

 nuclei and micronuclei are distributed by fission to difi^erent individuals, 

 the exact processes differing in different species. 



7. In conjugation, only nuclei are exchanged; each individual retains 

 its cytoplasm complete. Hence after conjugation each individual has a 



