METHOD OF OPERATION 131 



micronucleus were unaffected. When the macronucleus 

 disappeared, therefore, the acquired modifications also 

 disappeared. 



But disappearance of the macronucleus and its replacement 

 from the micronucleus are not all that occurs at conjugation. 

 There is also the exchange of half nuclei; so that each individ- 

 ual has a new combination of genie materials. This might 

 well give a new combination of characteristics, so that the old 

 characteristics, however acquired, might be no longer mani- 

 fested. The seeming loss of the acquired characters might be 

 due to this formation of a new combination of genie mate- 

 rials, rather than to the loss of the macronucleus. 



The difficulty here presented was overcome in the infuso- 

 rian Uroleptus by an experiment of Calkins. In a conjugating 

 pair from a depressed stock, by an operation Calkins pre- 

 vented the exchange of the half nuclei. The macronucleus 

 disappeared as usual, but the new one was formed from the 

 individual's own micronucleus, without aid from that of its 

 mate ; so that there was no new combination of genie mate- 

 rials. Yet the descendants of the individual in which this 

 occurred had lost their depression. With the disappearance 

 of the macronucleus the acquired modification likewise 

 disappeared. 



The same thing is shown to be true for the infusorian 

 Didinium by Calkins and by Beers. When the animals be- 

 come depressed through the action of bad conditions, they 

 become encysted, and while in the cyst the macronucleus 

 seemingly disappears and is replaced from the micronucleus. 

 At the same time the depressed condition of the organism 

 also disappears. 



In these cases then it appears probable that the modifica- 

 tion produced by the environment was only in the genie 

 materials of the macronucleus. The macronucleus is a transi- 



