654 ENDOMIXIS 



appears that intrinsic reorganization, as well as endomixis, meet the nor- 

 mal exigencies of existence and keep the race on the even tenor of its 

 way. For significant possibilities of genetic change in heterozygous indi- 

 viduals, however, reorganization is accompanied by synkaryon forma- 

 tion, either in autogamy or conjugation. 



Autogamy 



The first definite statement of autogamy in the ciliates was given in a 

 brief article by Fermor (1913), who described the degeneration of the 

 macronucleus and the origin of a new one from a synkaryon of micro- 

 nuclear origin, during the encystment of Stylonychia pustulata. But the 

 problem was not emphasized until Diller (1936) described autogamy in 

 P. aureUa and stated : 



I have not been able to confirm the micronuclear behavior which Woodruff 

 and Erdmann have described for endomixis in P. aurel'ia. In the failure of 

 such verification I am inclined to deny the existence of endomixis as a valid 

 reorganization process. I feel that Woodruff and Erdmann have combined 

 stages of hemixis and autogamy into one scheme, "endomixis," overlooking 

 the maturation and syncaryon stages in autogamy. 



And in regard to his own earlier description of endomixis in Trichodina 

 sp., Diller remarks, "It may be that hemixis and exconjugant stages were 

 lumped together as 'endomixis' in this account" (Figs. l60, l6l). 



In enthusiasm for the concept of autogamy, it may be well not to 

 exclude endomixis in P. aureUa — or Trichodina sp. — without careful 

 consideration, although there is no inclination to deny that autogamy 

 occurs in P. aureUa, in view of the combined data presented in the 

 cytological study by Diller and the genetical studies of Sonneborn 

 (1939a, 1939b, 1939c). However, Sonneborn's observations were not 

 made on the Yale race of P. amelia nor on the mating-type variety which 

 it represents, because there are as yet no known genes in this variety, 

 and such tests therefore cannot be made. 



In the opinion of the writer, the crucial cytological stages are not 

 absolutely demonstrated, in part because most of the animals were 

 taken from mass cultures and relatively few from isolated lines or from 

 pedigreed lines, and therefore the sequence of events. was not determined 

 from pedigreed series. To demonstrate satisfactorily the exact sequence, 

 it is necessary to follow critically the nuclear behavior in series of pedi- 



