2i6 BIOLOGICAL LECTURES. 



tion of chromosomes taking place. Representatives of this 

 stage are found chiefly in the Flagellata, although some Rhizo- 

 poda and some Ciliata show the same thing. Forms with this 

 permanently granular chromatin, again, are found in two con- 

 ditions. In one type the granules are scattered throughout 

 the entire cell, and are never confined by a nuclear membrane 

 (so-called " distributed " or " diffuse " nuclei). In nuclei of the 

 other type the granules are confined in a definite, more or less 

 spherical space, which may or may not be bounded by a nuclear 

 membrane. Examples of the first type were described by Gruber 

 in certain Rhizopoda and in a number of Ciliata, and, as he sug- 

 gested, it is highly probable that many, if not all, of Haeckel's 

 Monera will be found to possess nuclei of this type. Among 

 flagellated forms it has been described by Biitschli ('96) l for 

 Chromatium okenii and Ophidomonas jenensis, and by myself 

 ('98) 2 for a species of Tetramitus. In the latter form the gran- 

 ules of chromatin, which at first are scattered throughout the 

 entire cell with no apparent order, come together to form a 

 loose aggregate prior to division. In this condition the aggre- 

 gate is divided into halves, an equal portion going to each 

 daughter-nucleus (Fig. 2). It is important to note here, how- 

 ever, that another element comes in to complicate the process. 

 In the resting condition of the cells, when the chromatin is 

 distributed throughout the cytoplasm, a faintly staining body 

 can be found somewhere near the center of the cell (Fig. 2, A). 

 This body becomes more definite as the chromatin granules 

 come together for division, and it divides into two equal por- 

 tions before the nucleus is halved. During the process of 

 division the chromatin granules become heaped about this 

 partly divided body, one-half of which remains in the center 

 of each daughter-heap of granules until the end of the division 

 (Fig. 2, D, E}. After division the granules again separate, form- 

 ing the distributed nucleus. The central body, therefore, has 

 the attributes of an attraction sphere. 



The condition represented by this temporary aggregation of 

 chromatin granules about the sphere is permanent in the ma- 



1 Weitere Ausfuhrungen uber den Bau der Cyanophyceen und Bacterien. 

 Leipzig, 1896. 2 Ann. New York Acad. Sci. 1898. 



