REPRODUCTION 151 



after conjugation in Conchophthirus mytili and since in Colpidium 

 and Glaucoma, the chromatin elimination appears to be followed by 

 a high division rate and infrequency of conjugation. Dass (1950) 

 noticed a dark body between two daughter macronuclei of a ciliate 

 designated by him as Glaucoma piriformis and considered it as sur- 

 plus desoxyribonucleic acid about to be converted by the cytoplasm 

 to ribonucleic acid necessary for active growth. 



In Paramecium aurelia, Woodruff and Erdmann (1914) reported 

 the occurrence of "endomixis." At regular intervals of about 30 days, 

 the old macronucleus breaks down and disappears, while each of the 

 two micronuclei divides twice, forming eight nuclei. Of these, six 

 disintegrate. The animal then divides into two, each daughter indi- 

 vidual receiving one micronucleus. This nucleus soon divides twice 

 into four, two of which develop into two macronuclei, while the 

 other two divide once more. Here the organism divides again into 

 two individuals, each bearing one macronucleus and two micronuclei. 

 This process, they maintained, is "a complete periodic nuclear re- 

 organization without cell fusion in a pedigreed race of Paramecium." 

 The so-called endomixis has since been reported to occur in many 

 ciliates. However, as pointed out by Wilson (1928), Diller (1936), 

 Sonneborn (1947) and others, there are several difficulties in holding 

 that endomixis is a valid process. Diller considers that endomixis 

 may have been based upon partial observations on hemixis (p. 206) 

 and autogamy (p. 203). Sonneborn could not find any indication 

 that this process occurs in numerous stocks and varieties of Para- 

 mecium aurelia, including the progeny of the strains studied by 

 Woodruff, and maintained that endomixis does not occur in this spe- 

 cies of Paramecium. 



As has been stated already, two types of nuclei: macronucleus 

 and micronucleus, occur in Euciliata and Suctoria. The macro- 

 nucleus is the center of the whole metabolic activity of the organism 

 and in the absence of this nucleus, the animal perishes. The waste 

 substances which become accumulated in the macronucleus through 

 its manifold activities, are apparently eliminated at the time of 

 division, as has been cited above in many species. On the other 

 hand, it is also probable that under certain circumstances, the macro- 

 nucleus becomes impregnated with waste materials which cannot be 

 eliminated through this process. Prior to and during conjugation 

 (p. 188) and autogamy (p. 203), the macronucleus becomes trans- 

 formed, in many species, into irregularly coiled thread-like structure 

 (Fig. 85) which undergoes segmentation into pieces and finally is 

 absorbed by the cytoplasm. New macronuclei are produced from 



