218 BIOLOGY OF THE PROTOZOA 



two equal portions, one passing to each daughter cell (Fig. 35, p. 

 67). Band-form nuclei characteristic of Blepharisma, Spat Ind- 

 ium, Didinium, Vorticella, Euplotes, etc., condense into spheroidal 

 or ellipsoidal bodies before dividing. Where two macronuclei are 

 present in the usual vegetative cell, as in Oxytricha, Stylonychia, 

 Gastrostyla, etc., each divides independently of the other but syn- 

 chronously. As with band-form nuclei the beaded macronuclei 

 likewise form short rods as in Stentor, Spirostomum ambiguum, 

 etc., the beaded character in all cases being lost. Here the separate 

 beads are usually enclosed in a common nuclear membrane which 

 is constricted at intervals, the contained chromatin massing together 

 at the period of division. This is the condition in Uronychia trans- 

 fuga, also, the twelve to fourteen apparently separate macronuclei 

 are all connected, and the chromatin fuses prior to division to form 

 a relatively short ellipsoidal nucleus (Fig. 113). 



In other types, however, the multiple macronuclei are independent 

 and entirely disconnected. They arise by division and retain their 

 independence during vegetative life. Thus in Urolepius mobihs 

 and U. halseyi the eight or more macronuclei are formed as a 

 result of a fourth division of the single parental nucleus from 

 which they came (cf. p. 93 and Fig. 110). In preparing for division 

 of the cell each of these eight nuclei of Uroleptus undergoes a 

 remarkable transformation. A nuclear cleft (Kernspalt) appears 

 in each, and in the cleft is a single large granule. The major part 

 of the nucleus lies below the cleft and is filled with densely-staining 

 chromatin; the other part lying above the cleft contains much less 

 chromatin in the form of fine granules (Fig. 47). This latter part, 

 together with the granules in the cleft, is thrown off and the 

 chromatin contents are distributed in the cytoplasm. When each 

 of the nuclei is thus freed from its distal portion the eight remaining 

 parts fuse, forming first a long banded nucleus, and later, by con- 

 densation, a relatively small ellipsoidal and single nucleus. This 

 divides twice or three times before the division of the cell is com- 

 pleted, the fourth division always occurring after the daughter 

 cells have separated (Fig. 110). 



The micronuclei show no such complicated histories. If they are 

 multiple in the cell there is no fusion, nor is there any elimination 

 of micronuclear material. Each divides with the formation of an 

 unmistakable, but very minute, mitotic figure (Fig. 23, p. 50). 

 They are all represented furthermore by daughter halves in each 

 of the daughter cells. 



(b) Evidence of Cytoplasmic Reorganization. — Not only is there 

 evidence of change in the cytoplasmic makeup at division through 

 the distribution and absorption of nuclear material as in Urolepius 

 mobilis, but the entire cytoplasm shows other evidence at this 

 period. In all eiliates there is a more or less clearly marked antero- 



