No. 2.] CENMTROSOMES IN THE ANNELID EGG. 199 
Besides moving apart, the centrosomes migrate toward the 
centre of the egg, the male pronucleus accompanying them, 
sometimes on one side and sometimes on another, but always 
near at hand. Their final position is near the centre of the egg, 
on the side toward the polar globules. The central spindle, 
which has developed between them, lies at right angles to the 
egg-axis (Figs. 30, 36-38). After the centrosomes have sepa- 
rated a certain distance, the centrosphere disappears and the 
rays diverge from the centrosomes themselves. A lightly 
staining band—the incipient central spindle of the first cleavage- 
amphiaster — extends from one centrosome to the other (Figs. 
36-39). 
The rays of the sperm-asters become more and more exten- 
sive at the expense of the cytoreticulum until, at the time of 
the union of the pronuclei, they often extend to the extreme 
periphery and incorporate nearly all the cytoplasm of the egg. 
They are not straight but curved, those from either centrosome 
taking different directions, so that in certain portions of the 
egg the rays cross one another (Figs. 36—40). 
Since the central spindle and two centres of radiation lie on 
one side of the male pronucleus and in close proximity to it, a 
conical space on the opposite side of the pronucleus is left free 
from the rays (Figs. 38-40). In this space and between the 
rays in other portions of the egg, especially near the periphery, 
strands of cytoplasm may be seen running in various directions 
(Figs. 39, 40). The rays themselves are usually branched at 
the outer ends. The yolk-granules do not approach very near 
to the centres of radiation, apparently because the rays are too 
numerous or because the asters repel them. A few granules, 
however, are found in the conical space opposite the amphiaster 
and near the pronucleus (Fig. 38). 
The sperm-head, or male pronucleus, having grown to its full 
size, finally takes a slightly eccentric position in that radius of 
the egg which, if extended, would pass through the polar glob- 
ules, while near it lie the male centrosomes and the huge 
amphiaster just described (Figs. 34—40).} 
1 In the late stages (Figs. 36-38) there are variations in the relative position of 
the male pronucleus and amphiaster which show a certain degree of independence 
