128 GENETIC VARIATIONS 



The facts of inheritance at conjugation show with cer- 

 tainty that the genie materials in both the reserve nucleus and 

 the active nucleus help to control the characteristics, and they 

 strongly indicate that the genie products in the cytoplasm play 

 a part in this also. To see this, follow in the cross between a 

 Paramecium of a large race and one of a small race what 

 happens in the descendants of one of the individuals. For 

 this we may select the small individual B in Figure 19, above. 

 After conjugation it has a small body, composed of cytoplasm 

 containing genie substances that came from the nucleus of 

 the small parent B before it had conjugated. Its cytoplasm 

 likewise contains many dissolving pieces of the old macro- 

 nucleus of the parent B. All these parts tend to produce a 

 body that is small. It also contains a nucleus, half derived 

 from the large parent /4,half from 5. Incidentally, this nucleus 

 becomes later separated into its two parts, the minute reserve or 

 micronucleus and the large active macronucleus. This nucleus 

 tends to make the body large; in the long run it produces a 

 body of twice the length, and therefore eight times the bulk, 

 of this original B. But during the intervening three weeks, 

 while at least twenty generations are produced, the body does 

 not reach this size. It is intermediate between the size that 

 the new nucleus tends to produce, and the size that the 

 materials of the old body tend to produce. It is clear therefore 

 that the materials of the old body help during this period to 

 control the body size. But as generations pass the new nucleus 

 more and more dominates the body, until finally a size is 

 reached which is that due to the new nucleus; a size inter- 

 mediate between the sizes of the two parents. 



During this period of change, the organisms are regularly 

 dividing; some twenty or more generations are produced 

 before the final size is reached. At every division the original 

 material of the body is diluted to half its volume. After ten 



