336 LORANDE LOSS WOODRUFF 



and are present in a pedigree race of this organism which the 

 present writer now has under cultivation.^ It is also significant 

 that Miss Moody's race of Spathidium could not be induced to 

 conjugate, whereas the writer's culture conjugates successfully 

 at frequent intervals.^'' 



The evidence at hand certainly shows that races of free-living 

 ciliates exist whir-h do not exhibit the orthodox nuclear apparatus. 

 The evidence also indicates that amicronucleate forms are either 

 unable to conjugate or, if cell fusion does occur, the result is 

 abortive. It is certain that a morphologically defined micronu- 

 cleus is not necessary for the continued existence by vegetative 

 division of certain races of common free-living ciliates which 

 typically have this cell organ. 



If, on theoretical grounds, one is predisposed to believe that 

 the presence of 'germinal' chromatin (ordinarily segregated in 

 a micronucleus) is necessary for the life of the cell, then, since 

 amicronucleate cells live and divide, the nucleus which is present 

 must be regarded not as a macronucleus in sensu stricto, but as 

 an amphinucleus. If this interpretation is correct, the relation 

 between idio- and trophochromatin in the amphinucleus is appar- 

 ently of such a nature that the former is unavailable for the con- 

 jugation phenomena, since the evidence to date indicates that 

 conjugation either is not attempted or is abortive in amicronu- 

 cleate races. 



It is possible that amicronucleate races arise by the trans- 

 formation of all the micronuclei, resulting from the reconstruc- 

 tion micronuclear divisions after conjugation or endomixis, into 

 macronuclei. Such a result was observed by Prandtl in his 

 study of the cytology of conjugation in Didinium, though he 

 doubted if the animals with a nuclear heritage of this character 

 were viable. ^^ 



^ L. L. Woodruff and Hope Spencer, The structure and behavior of Spathidium 

 spathula with special reference to the capture and ingestion of its prey. Jour. 

 Exp. Zool. In press. 



^° L. L. Woodruff and Hope Spencer, The early effects of conjugation on the 

 division rate of Spathidium. Proc. Soc. for Exp. Biol, and Med., 1921, vol. IS. 

 The survival value of conjugation in the life history of Spathidium, Ibid., 1921, 

 vol. 18. 



" H. Prandtl, Die Konjugation von Didinium nasutum. Archiv f. Protistenk., 

 1906, Bd. 7, S. 251. 



