THE NUCLEUS 



85 



forms a new blepharoplast from its centrosome, and subsequently 

 a new flagellum ; or the blepharoplast of the parent cell divides 

 independently to form the blepharoplasts of the daughter-cells 

 (Fig. 43). In this last type, the blepharoplast, though obviously 

 a body of centrosomic nature, acquires a more or less complete 

 independence of the definitive centrosome, and becomes a distinct 

 cell-organ, permanent for at least a certain number of cell-genera- 

 tions ; it may multiply and undergo various structural complica- 

 tions, to be described presently. 



FIG. 42. Stages in the division of Spongomonas uvella. A, Resting condition of 

 the cell ; two flagella arise, each from one of a pair of blepharoplasts (diplo- 

 some) ; the nucleus contains a large karyosorne, in which the centriole is 

 lodged, and a few irregular grains of peripheral chromatin in the nuclear cavity. 

 B, Early stage of mitosis ; an achromatinic spindle is formed with the centrioles 

 at the poles, one centriole (on the right) having already divided into two ; 

 the chromatin, both peripheral and central, has united to form a dense 

 equatorial plate in which separate chromosomes cannot be discerned ; the 

 flagella have disappeared, together with their blepharoplasts. G, Similar 

 stage in which the daughter-flagella are growing out precociously from the 

 centrioles, one on the left, two on the right. D, Later stage in which the 

 equatorial plate has split into two daughter-plates, but no flagella have as 

 yet grown out from the centrioles, of which there are two at each pole. E, 

 Division of the nucleus nearly complete ; no flagella. F, Nucleus completely 

 divided, daughter-nuclei in process of reconstruction ; from each a pair of 

 blepharoplasts has been budded off, still connected by a centrodesmose with 

 the centriole contained in the karyosome ; a pair of daughter-flagella has 

 arisen from one pair of blepharoplasts, but not as yet from the other. After 

 Hartmann and Chagas (62), magnification about 2,400. 



3. In certain flagellates for example, trypanosomes and allied 

 forms (" Binucleata ") the cell-body contains two nuclei, as already 

 noted : a trophonucleus and a kinetonucleus. To what extent 

 these nuclei are provided with centrosomes is at present a little 

 doubtful ; probably this point is one which varies in different cases 

 (compare Wenyon, 84). There are, however, three chief possi- 

 bilities : (a) There may be but a single centrosome, that of the 

 kinetonucleus, which acts both as blepharoplast and division-centre 



