604 
T. H. MORGAN 
or that the oil itself slips away more easily than does the yolk, as 
the material wells up from the interior. The latter interpretation 
seems the more probable one. 
The sperm may be present in the egg when centrifuged, plate 2, 
fig. O. It may lie in any part of the egg without regard to the 
centrifuging, but is displaced from the oil and yolk areas. Despite 
the fact that the sperm head represents a compact mass of chroma- 
tin, its weight corresponds so nearly with that of the cytoplasm 
of the egg that the centrifuge fails to move it. As the sperm 
head absorbs fluid it may be found still at any point in the egg, 
but as soon as the absorption passes beyond a certain point the 
sperm nucleus becomes lighter than the cytoplasm and is carried 
to the oil pole. While still small it is often found lying between 
yolk and cytoplasm. I have never found it embedded in the yolk. 
I interpret this to mean that as the yolk granules collect at the 
outer pole the nucleus is displaced inwards. Since it has not been 
found in the oil, a similar explanation may apply here. 
My inability to move the sperm nucleus prevented an experi- 
ment that I had tried to carry out. Were it possible to move the 
sperm nucleus away from the sperm centrosome one might sepa- 
rate two factors, closely associated in normal development, 
and hope to discover whether a new centrosome would appear 
near the male nucleus, or whether the nucleus and aster find each 
other again. In the later stages of the male nucleus, when it is 
possible to perform the experiment, the asters are so near the cen- 
ter of the egg that the nucleus is within reach of their rays. I 
shall return to this point later. 
The first polar spindle extends almost throughout the entire egg. 
Its displacement is more difficult, perhaps in consequence of its 
extension, than in larger eggs with relatively smaller spindles. 
Soon after the egg is laid one end of its polar spindle comes nearer 
to the surface. If the egg be then centrifuged one of the following 
results may be observed : 
(1) Should the egg fall in the machine so that the spindle lies at 
the side, and therefore in the clear area, it is unaffected by the 
centrifuging, except in so far as passage of the yolk granules may 
be partly blocked by the central spindle ; or by the centers of the 
aster, so that granules may accumulate on their centripetal sides. 
