650 ENDOMIXIS 



these studies, it must be admitted, the authors failed to follow the 

 sequence of nuclear events in series of pedigreed animals, but fitted their 

 findings in isolated animals into the picture of endomixis as originally 

 portrayed. Three of these investigations are of particular significance 

 at the moment. 



Diller (1928), in a study of "binary fission and endomixis in Tricho- 

 dina from tadpoles," gives a categorical account of the reorganization 

 process. He shows the resolution of the macronucleus into chromatin 

 bodies: "In most cases the macronucleus breaks up completely by form- 

 ing numerous spherical bodies of varying sizes." And the origin of the 

 primordium of the new macronucleus is from a residual micronucleus : 

 "The final eight products of the micronuclear divisions are originally all 

 apparently similar. Seven of them, however, rapidly differentiate into 

 macronuclear Anlagen, while one remains the functional micronucleus." 

 The process is "characterized by the absence of maturation spindles and 

 synkaryon formation" (Fig. 157). 



Stranghoner ( 1932 ) , in a detailed description of endomixis in Parame- 

 cium multimicronucleatum , emphasizes the fact that "Im Gegensatz zur 

 Conjugation hildet der Macronucleus hei der Aujlosung ke'ine wurst- 

 jormigen Schiingen," and describes and figures the incorporation of 

 chromatin spheres from the old macronucleus into the new one (Fig 

 158). 



Kidder (1938) observes a "nuclear reorganization without cell divi- 

 sion in Paraclevelandia shnplex," in which the details of the process 

 are unique but the end result is the same. The old macronucleus elimi- 

 nates a large part of its chromatin and the remainder then becomes in- 

 corporated with one product of a single micronuclear division, to con- 

 stitute the primordium of the new macronuclear apparatus (Fig. 159). 



In this cooperation between macronucleus and micronucleus, de- 

 scribed by Stranghoner and Kidder as endomixis, we seem to have, as it 

 were, stages in the evolution of macronuclear metamorphosis intermedi- 

 ate between the intrinsic changes evidenced by reorganization bands, 

 direct elimination of material, and so forth, and the complete compe- 

 tence of the micronucleus alone to form a new macronucleus during 

 endomixis as it has been described in other species. 



That intrinsic reorganization is adequate for the continued life of 

 the race appears to be evident from the study of Dawson (1919) on an 



