206 MEAD. (Vou. XIV. 
in the line between the two new cells there appears a series of 
black granules, the foci of pencils of connecting fibres extend- 
ing in both directions to the nuclei (Fig. 51). These bodies 
later become aggregated at one place and form a large brown 
Zwischenkorper (staining like a centrosome), from which the 
rays diverge. In side view the Zwzschenkorper may always be 
seen to lie below a line connecting the centres of the nuclei; z.¢., 
nearer the vegetative pole. At this stage the nucleolar frag- 
ments of the original cleavage-nucleus lie in the larger of the 
two cells (Figs. 51, 52). Here they remain for a while, gradu- 
ally becoming smaller and less distinct, and vanish entirely 
before the karyokinetic figures are formed in the two blasto- 
meres. 
The centrosomes, which divided at an early stage and sepa- 
rated as the karyokinesis progressed, continue to move apart 
during the reconstitution of the nuclei, and a spindle develops 
between each pair. While the chromosomes are being trans- 
formed into vesicles the centrosphere at either end of the 
spindle disappears (Fig. 49), and the rays which now diverge 
from the centrosomes increase rapidly in length and thickness, 
and reach their maximum development in a late stage of the 
reconstitution of the nucleus, as is represented in Figs. 51 and 
52. They extend to the periphery of the egg and are easily 
distinguishable between the closely packed yolk-granules at the 
lower pole. They can be traced even through the substance of 
the yolk-lobe which develops on the lower hemisphere when the 
first cleavage-spindle is in an early stage (metaphase) and 
eventually becomes a part of the larger of the two blastomeres 
(see Fig. 50).!. The rays diminish in extent as the new nucleus 
assumes its definitive spherical contour; the centrosomes, mean- 
while, take their respective positions, nearly 180° apart, near 
the surface of the nucleus (Fig. 53). 
The reconstitution of the nuclei and the accompanying phe- 
nomena proceed simultaneously in the two blastomeres, and 
each is now in a stage of karyokinesis exactly comparable to 
that of the original odsperm after the union of the pronuclei. 
1 In a previous account of this phenomenon I said that the yolk-lobe was sepa- 
rated from the blastomere. This was a mistake, which I corrected in a later paper. 
