732 CALKINS. [Vol. XV. 



In the metaphase the centrosome can easily be identified in 

 all nuclei, whether undergoing vegetative or spore-forming divi- 

 sion, and in the latter it can be distinguished at all stages. In 

 spore-forming mitoses it divides early in the anaphase so that 

 single centrosomes are rarely seen. I have not observed its 

 division in the anaphase of vegetative mitoses ; it probably 

 remains undivided until the prophase of the next division. In 

 the metaphase the double centrosome lies in the inside of the 

 sphere, but usually in an eccentric position (Fig. 38). In Fig. 

 38 (a mitosis in a spore-forming cell) the two daughter-centro- 

 somes lie close together and separation would take place later 

 in a direction at right angles to the plane of the paper. The 

 preceding division is just finished, and the daughter-centrosomes 

 have divided for the ensuing mitosis. 



The daughter-centrosomes divide in the early anaphase, after 

 which they lie more nearly in the center of the sphere (Figs. 28 

 and 31), and, as a rule, they remain near the center until the 

 division is complete (Figs. 23 and 39). They may lie eccen- 

 tricly, however, even in the telophase (Fig. 24), but in this 

 case it is away from the nucleus. Except for the mantle-fibers, 

 the centrosome is in no way the center of a radial system ; the 

 sphere lies around it as an inert undifferentiated mass. 



The centrosome appears to vary somewhat in form and in 

 size. In some cases it is comparatively large and round (Fig. 

 24) ; in others it is round but much smaller (Figs. 23, 39); 

 while in still other cases it is irregular in outline or even tri- 

 angular (Fig. 38). 



In the resting cytoplasm I have failed completely to find a 

 centrosome in the sphere. In the resting nucleus, however, 

 there is a minute body which stains intensely with the iron 

 haematoxylin and which differs considerably in appearance from 

 chromatin granules (see p. 7). This body disappears during 

 the chromosome-formation and is not seen again until the 

 nucleus reforms after division (compare Figs. 3, 4, 6, 7 with 8, 

 9, 10, II, etc., where chromosome-formation has begun). It can 

 always be distinguished from the chromatin granules by its luster 

 and small spherical form. It takes no part in spireme-formation, 

 but remains a separate element (Figs. 6 and 7). At the begin- 



