ENDOMIXIS 



55 



intervals, the macronucleus degenerates, and is replaced from the 

 microniicleus as at conjugation. Woodruft' and Erdmann (1914) described 

 the process in Paramecium aurelia, and named it endomixis. P. aurelia 

 contains normally two micronuclei and one macronucleus (Fig. 34). When 

 endomixis occurs, the macronucleus disintegrates and is eventually 

 absorbed. The two micronuclei divide to form four, and these again to 

 form eight micronuclei. Of the four derived from each original micro- 



<g5Vb6?Vb> C 



Fig. 34. — Endomixis in Paramecium aurelia: Diagrammatic Representation 

 OF Nuclear Changes as described by Woodruff and Erdmann , 

 1914. (After Jennings, 1920.) 



A-B. Degeneration of macronucleus and first division of two micronuclei. 



C-D. Second division of micronuclei and degeneration of .six of the daughter micronuclei. 



E. Division of ciliate to produce two daughter individuals each with a single micronucleus. 



F-G. Two divisions of micronuclei to give rise to four, two of which increase in size to become 



macronuclei. H. Further division of micronuclei. 



I. Division of ciliate to give rise to the normal type as at A. 



nucleus, three degenerate, so that two micronuclei are left. The ciliate 

 now divides, giving rise to two ciliates, each with a single micronucleus. In 

 each of these daughter ciliates the micronucleus divides to form two, and 

 again to form four micronuclei. Two of these increase in size and become 

 macronuclei, while the other two divide to form four micronuclei. The 

 ciliate now has two macronuclei and four micronuclei. It now divides to 

 form two ciliates, each of which has two micronuclei and one macronucleus 

 as in the original form. 



