196 MEAD. [VoL. XIV. 
These two primary asters (‘primary mechanical centres,” 
Reinke, '94) arise at some distance from the wall of the germi- 
nal vesicle, and usually about ninety degrees from each other, 
though they may be nearer together or even farther apart. I 
am not prepared to say at present whether the primary asters 
are formed by the further growth and specialization of two 
of the secondary asters or by the union and coalescence of 
several. 
The nuclear membrane regains its regular contour when the 
multiple asters have vanished, except for a deep sinus in the 
vicinity of each of the two primary asters (Figs. 8,9). A well- 
defined centrosome, staining dark brown, now appears in the 
centre of each aster, surrounded by an area of lighter color 
(centrosphere) from which the large granular astral rays diverge 
in all directions. These are the centrosomes and asters of the 
jirst maturation-spindle (Figs. 9-13). The centrosphere always 
stains brown, though very much lighter than the centrosome. 
The rays from the two asters give the appearance of actually 
pushing in the nuclear membrane, though the latter remains 
for a while intact. 
The rays of the two primary asters are many of them coarse 
and quite extensive (Fig. 9). They do not, however, reach the 
periphery, but break up into the network which extends through- 
out the whole cytoplasmic portion of the egg. Eventually the 
nuclear membrane disappears, though the region corresponding 
to the germinal vesicle still takes a stain different from the 
rest of the protoplasm and has also a different texture 
(Pigs: 10;"11). 
Between the two asters a spindle is formed which remains 
for some time near the vanishing germinal vesicle, but at right 
angles to the radius of the egg. The rays from the asters enter 
the region of the vesicle, the chromosomes gather at the equator 
of the spindle, and the latter gradually swings around to its 
definitive position, perpendicular to the surface of the egg 
(Figs. 10-13). The nucleolus, meantime, breaks up into a 
number of pieces which remain for a time in the vicinity of the 
spindle, but gradually degenerate and disappear. The centro- 
somes divide very early before the spindle begins to move 
