ENDOMIXIS 653 



amicronucleate race of Oxytricha hymenostoma, in which, obviously, a 

 micronuclear reserve could play no part. Woodruff's work (1935) on a 

 race of Blepharisma undulans, without endomixis or autogamy, and 

 D. Young's findings (1939) on the same race, showing the elimination 

 of material from the macronucleus during division, support this thesis. 

 However, these results might be anticipated because several species 

 have been cultured for long periods without showing any evidence of a 



Figure 159. Endomixis in Paradevelandia simplex. 1, pre-q'stic form (the macronucleus 

 differentiating into degenerating posterior, and reorganizing anterior chromatin; the mi- 

 cronucleus in prophase) ; 2, later stage (the micronucleus in anaphase; further differentia- 

 tion of macronucleus) ; 3, telophase of the micronucleus (note the smoothly granular an- 

 terior half of the macronucleus) ; 4, fusion of daughter micronucleus with reorganized por- 

 tion of macronucleus (posterior portion of macronucleus shrinking away from the old 

 nuclear membrane; enlarged condition of the daughter micronuclei quite characteristic). 

 (From Kidder, 1938.) 



reorganization process, either intrinsic or endomictic, in the free-living 

 animals, and probably none occurs. As examples, reference may be made 

 to the work on Spathidium spathula by Woodruff and Moore ( 1924) , on 

 Paramecium calkinsi by Spencer (1924), and on Didinium nasutum 

 by Beers (1929). In regard to reorganization by endomixis, the culture 

 of P. caudatum studied by Metalnikov (1937), and the (to date) 

 thirty-three-year-old culture of P. aureiia at Yale University may be cited, 

 unless the future should prove that autogamy, to the exclusion of en- 

 domixis, occurs in these species (Woodruff, 1932). 



Thus in the species in which reorganizational phenomena occur, it 



