350 GARY N. CALKINS 



by a second division of the first two. One or two of these four 

 may degenerate; one or two may form macronuclei. Or the four 

 may divide again, forming eight nuclei before differentiation be- 

 gins. In Anoplophrya branchiarum and in Euplotes patella two 

 of the four nuclei degenerate, the other two form one macronu- 

 cleus and one micronucleus. In Colpidium colpoda (Hoyer, 

 '99), Stylonychia pustulata (Maupas, '88) and in Lionotus fas- 

 ciola (Prowazek, ,'09), only one of the four degenerates, two be- 

 come functi(^nal micronuclei, and one becomes the macroriucleus. 

 In Didinium nasutum (Prandtl, '06), Paramecium bursaria 

 (Hamburger, '04), Glaucoma scintillans (Maupas, '88), Leuco- 

 phrys patula (Maupas), Spirostomum teres (Maupas), and in 

 Stylonychia pustulata (Maupas), two of the four nuclei become 

 macronuclei and two become micronuclei, none of the nuclei 

 degenerating. In Blepharisma undulans (Calkins, '12) all four 

 of this stage become macronuclei enclosing the micronuclei. 



In another group the first four nuclei divide once again before 

 the nuclei are differentiated. Here we find Paramecium cauda- 

 tum, Paramecium putrinum, Cryptochilum nigricans, Carchesium 

 polypinum, Vorticella nebulifera, and Ophrydium versatile. In 

 the last three mentioned, seven of the eight nuclei form macro- 

 nuclei. These fuse to fofm one in Cryptochilum (Maupas), but 

 in the other three forms they remain separated and are distrib- 

 uted to the daughter cells by unequal division until each cell 

 has one (Maupas, Kaltenbach, Popoff). In Paramecium cauda- 

 tum and in P. putrinum, four of the eight nuclei form macronuclei, 

 while the fate of the other four is differently interpreted. Mau- 

 pas ('88) and Doflein Cll) hold that three of these degenerate, 

 leaving one functional micronucleus. Calkins and Cull ('07) 

 find that all four are functional. 



An exceptional history is shown in the reorganization of Bur- 

 saria truncatella. Here no differentiation occurs until sixteen 

 nuclei are formed (Prowazek, '99). Two to five of them form 

 macronuclei, three or more form micronuclei, and tKe remainder 

 degenerate. 



In Uroleptus mobilis differentiation of the nuclei occurs with the 

 second division of the fertilization nucleus. One of the two nuclei 

 formed by the first division divides unequally into a large vesicu- 



