PHENOMENA ACCOMPANYING FERTILIZATION 



53- 



heteropolar spindle and divides into two unequal products the larger 

 of which is vesicular and persists as the new macronucleus, the 

 smaller one is spheroidal and compact and ultimately disappears 

 by absorption (Fig. 225, 4). The young macronucleus sometimes 



Fig. 225. — Origin of macronucleus after conjugation in Uroleptus mobilis. (1) 

 first metagamic mitosis of the amphinucleus; (2) one of the progeny of this division 

 dividing again; (3), (4), (5) telophase stages of second division of the amphinucleus 

 resulting in a new macronucleus (above), and a degenerating nucleus (below); (6 to 

 10), stages in differentiation of the young macronucleus and disintegration and 

 absorption of the old macronucleus; in (10) two new micronuclei are in mitosis pre- 

 paratory to the first division of the ex-conjugant. (M) new macronucleus; (m) new 

 micronuclei; (d) degenerating old macronuclei. (After Calkins.) 



called the "placenta" becomes finely granular and loses its staining 

 capacity which is not regained for a period of from three to five or 

 more days. During this period the young macronucleus appears 

 like a vacuole in a center of a cell and is distinctly visible in the 

 living cell. It is small at first but grows in size from day to day 



