No. 2.] CENTROSOMES IN THE ANNELID EGG. 205 
462), where they remain during the succeeding stages of mitosis 
(Figs. 48-52). 
The centrospheres reach their greatest development toward 
the end of the anaphase, though the radiations at this time are 
not so extensive (Figs. 462-48). The centrosomes, which 
divided very early, continually move apart within the centro- 
sphere without in the least altering the regular contour of the 
latter. In the early stages a line joining the two centrosomes 
would nearly coincide with the spindle-axis, but as they move 
apart they also swing around through an angle of about 9go° 
(Figs. 44-48). The distance between the centrosomes within 
the centrosphere is in definite and constant relation to the 
successive phases of mitosis, and one can predict the position 
of the chromosomes from the examination of the centrosomes, 
and vice versa. The centrosphere is smaller in the end of the 
spindle which belongs to the smaller cell (Figs. 46, 464, 48). 
The dark brown centrosomes are especially distinct during 
these stages in contrast to the light yellow centrosphere. In 
some preparations a minute halo surrounds each centrosome 
(Fig. 46), and in the later stages of the anaphase, before the 
centrosome disappears, a band of fibres, the incipient central 
spindle of the next mitosis, is demonstrable between them 
(Figs. 46%, 47). ’ 
When the rod-like chromosomes have reached a position near 
the centrosphere they gradually become vesiculated. Each 
chromosome at first appears as a double row of granules, sepa- 
rated by a longitudinal cleft (Fig. 48), but later the regular 
arrangement of the granules is lost, and each chromosome con- 
tinues to swell up and forms an oval vesicle (Fig. 49) resembling 
a miniature nucleus. I have several times counted the vesicles, 
and always found them to be eighteen. They arrange themselves 
in the form of a disc, and for some time the fibres of the cen- 
trosphere may be seen between them (Fig. 49). As they grow 
still larger they coalesce, not into a single mass, but into several 
irregular masses which themselves fuse to form a spherical 
nucleus (Figs. 50, 51). 
The cytoplasmic portion of the egg becomes pone ered 
during the later phases of the reconstitution of the nuclei, and 
