130 GENETIC VARIATIONS 



It is clear that the acquired characters do not disappear in 

 any such brief time as thirty days; on the contrary they may 

 persist for many months. This appears to be strong evidence 

 against the limitation of the environmental effect to the 

 cytoplasmic genie materials. 



At certain times in the course of generations, as w^e have 

 seen, the large macronucleus disappears; it breaks into 

 pieces, and these are absorbed, though they may remain for 

 a few days in the cytoplasm. This leaves the micronucleus as 

 the only nucleus. If the modifications resulting from the 

 action of the environment are limited to the active genie 

 substances of the macronucleus, they should disappear w^hen 

 the macronucleus disappears; or at least a little later, after its 

 pieces in the cytoplasm have disappeared. At this time the 

 acquired characters should be lost. 



Sometimes the acquired characters are indeed lost when 

 the macronucleus is lost. At the time of conjugation the 

 macronucleus is lost in both individuals, and is replaced from 

 the new nucleus formed from the union of the two half nuclei 

 — one half from each of the individuals of the pair. 



And at conjugation certain of the inherited modifications 

 partly or entirely disappear. This is true to a large extent of 

 the injurious modifications resulting from bad living condi- 

 tions. They often almost or quite entirely disappear when con- 

 jugation occurs, so that conjugation has been said to cause 

 "rejuvenescence." The animal after conjugation regains its 

 original high level of vitality, even though it remains in the 

 conditions which brought about the injuries. It is also true 

 that the increased resistance produced by long subjection to 

 certain chemicals, or by heat, often disappears at conjugation. 

 Since the macronucleus disappears at the same time, this 

 could be held to indicate that it is the genie substances of the 

 macronucleus that have been modified, while those of the 



