58 



BIOLOGY OF THE PROTOZOA 



distinguished from other substances of the resting nucleus by their 

 color reactions to basic and acidic dyes. Sometimes the chromo- 

 meres or chromioles are apparently suspended in a more or less 

 definite "linin" reticulum which is recognized as being a coagulation 

 product of the colloidal ground substance or karyolymph. In other 



Fig. 27. — 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 

 preparatory to the first division of the ex-conjugant. (At) new macronucleus; (m) new 

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



cases they are combined with the substance "plastin" to form a 

 clearly-defined endosome (karyosome) which, depending apparently 

 on the relative proportions of plastin and chromatin, may or may 

 not be visible in life. Plastin appears to be a well-defined nuclear 

 substance and writers generally speak of it with familiar ease, 



