1915] Lorande Loss Woodruff 375 



were never observed in this race of Paranicucmm, we early noted 

 " that various nuclear changes which are not at present recognized 

 occur normally in the life history of Paramceciiim" ; and we sug- 

 gested that possibly, when conjugation is prevented, a reorganization 

 of the nuclear apparatus within the individual cell occurs.® Erd- 

 mann independently reached an essentially similar position from a 

 consideration of the ptiblished data on this culture and a critical 

 study of infusorian life histories; and further, in an experimental 

 study of Amceba diploidea, suggested that a relation exists between 

 sexual phenomena and rhythms.'^ Accordingly, we collaborated 

 in a study of the daily cytological changes of this race of Paramcs- 

 cium during a period of six months, and discovered that the rhythms 

 in the division-rate are the physiological expression of internal 

 phenomena which involve the formation of a complete new nuclear 

 apparatus, by a definite sequence of normal morphological changes 

 that simulate conjugation.^ This nuclear reorganization, which 

 we term endomixis, consists, in essence, of a gradual disintegration 

 and absorption of the macronucleus in the cytoplasm. Simultane- 

 ously, a multiplication of the micronuclei is in progress. Certain 

 of the resulting micronuclei degenerate while the remaining one 

 (or two) form the new macronuclear and micronuclear apparatus. 

 This results in the reorganization of the cell without the fusion of 

 two animals. 



An essential morphological difference between endomixis and 

 conjugation is the absence of the third micronuclear division, which, 

 in conjugation, forms the stationary and migratory micronuclei; 

 and, of necessity, the non-formation of a syncaryon. After conju- 

 gation the reorganized cell has a new macronuclear and micronu- 

 clear apparatus, composed of combined material from the conju- 

 gants, while, after endomixis, the reorganized cell has a new 

 macronuclear and micronuclear apparatus composed of material from 

 its own micronuclei. In a word, the essential distinctive features 

 of endomixis are the absence of the third micronuclear division and 



^ Woodruff : Amer. Naturalist, 1908. 



■^ Erdmann: Ergeb. d. Anat. u. Ent., 1908; Archiv, f. Protistenk., 1913. 

 8 Woodruff and Erdmann: Proc. Soc. Exp. Biol. and Med., 1914; Journ. 

 Exper. Zool., 1914; also Erdmann and Woodruff: Biol. Cent., 1914. 



