72 BIOLOGY OF THE PROTOZOA 



statement is usually made that macronuclei arise from micronuclei, 

 a statement which is not strictly accurate, since the fertilization 

 nucleus is neither one nor the other, but merely a cell nucleus of an 

 unorganized individual. In some cases macronuclei and micro- 

 nuclei are not differentiated until the third division of the fertiliza- 

 tion nucleus (e g., in Cryptochilum nigricans, Paramecium caudatum, 

 Par. yntriniim, Bursaria truncaieUa, Carchesiwn 'polyiylmmi, Oper- 

 cularia coarctata, Ophrydium versatile, Vorticella monilata, V. nehu- 

 lifera, etc.); in other cases differentiation occurs after the second 

 divisions (e. g., in xinojjiophrya branchiarum, Colpidium colpoda, 

 Didinium nasutum, Glaucoma scintiUans, Leucophrys patula, 

 Lionofus fasciola, Paramecium aurelia. Par. bursaria, Blepharisma 

 undidans, Splrostomum teres, Euplotes patella and cJiaron, Onycho- 

 dromus grandis, Sfylonychia pustulata, Uroleptus mohilis, etc.); and 

 in still other cases the differentiation takes place after the first divi- 

 sion (e. g., ChiJodon uneinatus). In all cases both macronucleus 

 and micronucleus are formed by metamorphosis of such products of 

 division of the original nucleus after conjugation, the former by a 

 remarkable increase in size and in quantity of chromatin, the latter 

 by reduction in size and concentration of the chromatin; the former 

 becomes a metabolic organoid of the cell, the latter a germinal 

 organoid homologous with the. chromidiosomes representing idio- 

 chromatin of the rhizopods. 



A suggestive history of differentiation of macronuclei and micro- 

 nuclei is afforded by Blepharisma undidans Here, after two divi- 

 sions of the fertilization nucleus, each of the four products gives 

 rise not by a third division, but apparently by chromatin transfusion, 

 to a large, homogeneous and at first feebly -staining body originally 

 called a "placenta" by Biitschli. The exuded, peripheral chromatin 

 later metamorphoses into the large granular chromidiosomes charac- 

 teristic of the massive iyjye of macronuclei, while the original central 

 nucleus, like an endosome, is contained within it where it condenses 

 to form the minute micronucleus (Figs. 31 and 32). A similar 

 hiding place may account for the apparent absence of micronuclei 

 in forms like Actiiiobolus radians, Lacrymaria olor, Didinium nasu- 

 tum, etc. Amicronucleate races of ciliates, however, have been 

 cultivated by several observers: Didiniuin by Patten (1921); 

 Oxytricha fallax by Woodruff (1921); 0. hymenostoma by Dawson 

 (1919); Paramecium caudatum by Landis (1920) and Woodruff 

 (1921); Spathidium spathula by Moody (1912); and Urostyla 

 grandis by Woodruff (1921). This condition probably arises by 

 faulty reorganization after conjugation, but is also characteristic 

 of old-age ciliates. 



Endosomes are comparatively rare in these dimorphic nuclei but 

 may be present in the form of (?) plastin nucleoli (macronucleus of 

 Epistylis plicatilis according to Schroder), or as endobasal bodies in 



