124 GENETIC VARIATIONS 



and at conjugation; the successive figures from left to right show the 

 changes as time passes (see text). Diagram constructed from the 

 measurements made by De Garis. 



Thus after conjugation the new nucleus, formed half from 

 one of the mates, half from the other, begins to take control 

 of the body, gradually changing its characteristics. At the end 

 of a period of three or four weeks the descendants of the two 

 mates are alike in their characteristics. All this shows that the 

 inherited characteristics finally depend on the nature of the 

 genie materials contained by the nucleus. 



Now let us look at the relation of these things to the inher- 

 ited characteristics acquired under the action of the environ- 

 mental conditions. Have the environmental conditions 

 changed the nature of the genie materials present in the 

 nucleus, thus giving rise to new inherited characters ? 



To get evidence on this question certain further details 

 must be examined as to the conditions affecting genie mate- 

 rials in these organisms. In such Protozoa as Paramecium we 

 find that the genie materials are separated into active and 

 reserve portions. The active and reserve parts are separated 

 into two distinct nuclei, though these are produced by the 

 division of an original single one. 



Immediately after conjugation, as we have seen, each 

 infusorian has a single nucleus, formed by union of halves 

 from the two individuals that have conjugated. This nucleus 

 now divides into two, one of which remains as a small reserve 

 of genie materials, while the other grows large, and its genie 

 materials become active in the life of the individual. The 

 small reserve nucleus is known as the micronucleus ; the 

 large active one as the macronucleus. From the macronucleus, 

 genie materials pass out into the rest of the cell, interacting 



