306 GARY N. CALKINS 



due, probably, to absorption, for pale micronuclei are frequently 

 found in addition to the densely staining mitotic nuclei. At any 

 rate, when the macronucleus is ready for division, as in the later 

 coalescence phases, there are only two micronuclei. Their divi- 

 sion is completed prior to division of the macronucleus, the four 

 daughter nuclei always forming a characteristic linear group on the 

 side of the macronucleus (fig. 11). These daughter nuclei pass 

 directly from the telophase of the first division to the metaphase 

 of the second, as indicated by the absence of resting nuclei dur- 

 ing these stages. The second division may result in eight nuclei 

 (figs. 14 and 15), or one of the four may disappear while the 

 remaining three divide, thus giving rise to six micronuclei (fig. 

 12). If eight are formed, two of them disappear and six are 

 left; finally these six divide for the third time, forming twelve 

 micronuclei, and the cell, now ready for division, contains two 

 sets of six, one set passing to each daughter individual (figs. 

 16 to 18). In some young daughter cells there are only four 

 micronuclei (figs. 17, 19, and 21); in others there are six (figs. 

 16 and 18), and in others there are only five. • These variations 

 are probably due to the earlier or later disappearance of the mi- 

 cronuclei. The normal number would be eight had none dis- 

 appeared, this number agreeing with the number of macronuclei. 

 In the majority of hypotrichous ciliates the typical arrangement 

 is one micronucleus for each macronucleus, but here the charac- 

 teristic pairing is lost. The disappearance may be due to ab- 

 sorption of the nuclei in the cytoplasm, abundant evidence for 

 which is given by the frequent presence of faintly staining nuclei. 



^Vhile the nmiiber is thus variable, the great majority of the 

 individuals studied have only four micronuclei (figs. 1 and 21). 



The formation of the mitotic spindles is the same throughout. 

 The nucleus first swells in size, losing its characteristic homoge- 

 neous structure, and becomes vesicular. The chromatin is, at 

 first, in the fonii of eight (?) granular masses which may become 

 four double smooth, and homogeneous rods stretching from pole 

 to pole, or combinations of double and single rods may occur 

 Whether these rods are divided transversely or longitudinally 

 cannot be determined owing to their minute size and densely 



