506 J. A. DAWSON 



ism. It is probable that this form at some time in its history 

 contained a micronucleus, though it is of little value to speculate 

 concerning the manner in which the present amicronucleate 

 condition arose, since there are no data at hand. Such a con- 

 dition might cohceivably arise by some abnormal process during 

 conjugation which resulted in suppression of differentiation 

 between macro- and micronuclear material. 



Although the significance of the process of conjugation has 

 been exhaustively studied since Maupas' time, a complete solu- 

 tion of the problem has not as yet been obtained. The existence 

 of a form which not only apparently may live indefinitely without 

 conjugation, autogamy, or endomixis (assuming the possibility 

 of the latter phenomenon in an hypotrichous form), but also 

 apparently does not possess the ability to undergo any of these 

 phenomena, brings to light an entirely new possibility in the 

 life-history of ciliates. It has been proved quite conclusively 

 (Woodruff, '14) that in forms which ordinarily conjugate, the 

 continued prevention of this process brings about no loss of 

 viability if a favorable environment be provided. However, in 

 the organism under consideration there is apparently no possi- 

 bility not only of conjugation or endomixis, but also of 

 autogamy, and thus w'e have from another source crucial 

 evidence that none of these phenomena is an indispensable 

 factor in the life-history of this hypotrichous form. 



6. SUMMARY 



1. A pedigreed culture of Oxytricha hymenostoma has been 

 carried for 289 generations, from July 10, 1917, to November 17, 

 1917, and since that time to date (April 30, 1918) by means of 

 small mass cultures in petri dishes. 



2. A micronucleus has not been seen at any time in any of the 

 animals during the history of the cultures. 



3. Syngamy has not occurred during the course of the experi- 

 ments, although it is believed that the animal has frequently 

 been in a physical state similar to that in which syngamy takes 

 place. 



