igo 



THE PRO7OZOA 



split, which the Germans call a Kernspalt and the French a fente. 

 While this peculiar feature of the nucleus has not been explained, 

 what may be an important light has been thrown upon it by Bal- 

 biani ('95), who described the appearance as due to the presence of 



two materials within the nuclei, one 

 of which is chromatin, the other, 

 achromatic material or archoplasm. 

 This interpretation, however, cannot 

 be accepted as final. 



While the macronuclei are, as a 

 rule, single in number, the micro- 

 nuclei are often multiple. Probably 

 all Ciliata have at -least one micro- 

 nucleus, although the small size and 

 the extreme difficulty in staining 

 sometimes render it hard to find. 

 In one case at least (Opalina rana- 

 rum) there is only one kind of nu- 

 cleus. The number of micronuclei 

 is usually greater where the macro- 

 nucleus is elongate, and especially 

 where it is beaded (Stcntor, Spiro- 

 stomum, etc.). As a rule the micro- 

 nuclei are closely attached to the 

 membrane of the macronucleus, 

 occupying a minute indentation in 

 the latter, but in some cases they 

 are well separated. In form they 

 are round, ellipsoidal, or spindle- 

 shaped, but the form varies with the 

 nuclear activity, and does not mean 

 much in itself. Their longest axis 

 measures from i /u to 10 /x, and like 

 the macronuclei, they are covered 

 with a distinct membrane, while 

 the chromatin is usually massed at 



. LoxophyllummeleagrisQ>.f.^A. Some part of the nucleus. In Cer- 



D 



Fig. 



[BALBIANI.] 



tain cases the appearance is like 



A. Vegetative nuclei with chromatin in the ., c 4-u i vu *u 



form of a permanent spireme. B.C,D. The that f the macronudeUS With the 



same in division. chromatin in the form of a densely 



packed reticulum, giving to it a mas- 

 sive appearance. Here two distinct portions, the chromatin and 

 achromatin, can be made out (Fig. 105). 



Division of the nuclei takes place by mitosis in the micronuclei, and, 



