168 TRANSACTIONS OF THE [may 11, 
mitosis. This incipient amphiaster, if it may be so called, never 
progresses so far as to show spindle fibers. A third mitosis in- 
volving the egg centrosome does not, however, occur; for soon 
after the above described stage and before the meeting of the 
pronuclei both centrosomes with their surrounding atmospheres 
and asters, degenerate and disappear. This doubling of the cen- 
trosome seems too orderly to be a commencing fragmentation 
preparatory to degeneration, and one cannot avoid the thought 
that it may be a reminiscence of some ancestral process such as 
a parthenogenetic division or possibly a ‘ quadrille” such as 
Fol has described. 
A somewhat later stage shows the chromosomal vesicles 
formed and closely crowded. All that is now left of the egg 
center are a few indistinct rays. A little later Fig. 10, even 
these disappear and the vesicles show no trace whatsoever of 
aster, rays, or center of activity connected with them. More- 
over previous to their disappearance these radiations, in connec- 
tion with the female vesicles, are seen lagging behind the latter 
on the side removed from the male pronucleus. The sperm 
center at this stage (Fig. 10) consists of two powerful asters 
with focal centrosomes, at the poles of a hemispherical pro- 
nucleus. 
The foregoing observations show conclusively, as I believe, 
that the egg centrosome persists throughout all the maturation 
stages, but thereafter disappears. In the cleavage stages its 
place as directive center in cell division is taken by the sperm 
centrosome. The sperm asters can be traced throughout all the 
subsequent fertilization stages; their foci at no time show any 
such disturbance or sudden doubling or increase in size of the 
centrosomes, as would be expected did the egg center join or 
fuse with them. 
THe SPERM CENTROSOME. 
For some time after its entrance into the egg the spermhead 
shows no trace of archoplasmic mass, centrosome, or radial ar- 
rangement in the surrounding cytoplasm, but lies as a large 
homogeneous spherical body, somewhat roughened on its peri- 
phery, and staining intensely black by hematoxylin. It is sit- . 
uated somewhat eccentricly within a surrounding clear area. 
In this condition it remains for some time. The first appear- 
ance of the aster is at the extremity of a small process that 
arises from the spermhead. In the stage figured this is directed 
forward toward the center of the egg, but in one or two earlier 
preparations it appeared to be situated at one side and directed 
tangentially. This fact may indicate that the spermhead ro- 
