GENERAL CONSIDERATIONS 



37 



loss and replacement of the old macronucleus, and so forth. Renewed 

 vitality may be due to one or to both of these phenomena. Conjugation 

 differs from endomixis mainly in gelatinization of the cortex and in 



.«^ 





Figure 14. Uroleptus mobilis Engelm. Formation of new macronucleus after conjuga- 

 tion. 1. First metagamic or zygotic division of the amphinucleus; 2. One of the progeny 

 of this division dividing again; 3, 4, 5, telophase stages of this divison resulting in a 

 new macronucleus (above) and a degenerating nucleus (below) ; 6 to 10, stages in the 

 differentiation of the new macronucleus and disintegration and resorption of the old 

 macronucleus. In 10, two new micronuclei are in mitosis preparatory to the first division 

 of the ex-conjugant. (After Calkins, 1919.) 



amphimixis. Fertilization, with its sequelae of hereditary possibilities, 

 is a highly important result (see Jennings, injra, Chapter XV; and 

 Sonneborn, injra, Chapter XIV). It is also assumed to be the raison 



