6 INTRODUCTION. 
segment or daughter chromosome forms one-half of the ring, or 
each may be in the form of a short, thick U (Fig. 2, F). Sixteen 
chromosomes, the reduced number, are present in the first mitosis. 
While on the way to the poles the daughter chromosomes sometimes 
fuse with one another to form large masses.!_ This is especially so in 
the second mitosis, 
In the construction of the daughter nuclei, one or more larger masses 
of chromatin are formed by the chromosomes; a nucleolus appears 
near the chromatin mass or masses, and a nuclear membrane is laid 
down (Fig. 2,G). The membrane is unquestionably formed through 
the agency of the kinoplasmic fibers. The centrosomes increase in 
size, and the polar radiations are more distinct than in the spindle 
stage. The connecting fibers usually persist until the nuclear mém- 
brane is present, but a little later they disappear entirely. The chro- 
matin mass, gradually becoming less dense, soon disintegrates, and 
each daughter nucleus passes into the resting condition (Fig. 2, G). 
From the preceding it will be seen that each daughter nucleus is 
provided with one centrosome, but in the first mitosis the centrosomes 
could not be made out until they were on opposite sides of the nucleus 
and provided with radiations. The question naturally arises: Does 
the centrosome divide to give rise to the two daughter centrosomes? 
Swingle (’97), who has traced the persistence of the centrosome 
through several successive generations of vegetative cells in Stypo- 
caulon, one of the Pheophycee, found that a division of the centro- 
some takes place, and Strasburger (’97) arrives at the same conclusion 
as regards Fucus. This is the generally accepted view. 
We shall trace the early development of the spindle in the second 
mitosis in the tetraspore mother-cell in order to see what evidence is 
furnished by Dzctyota toward thé solution of this problem. 
During the reconstruction of the daughter nucleus (Fig. 3, H) 
two rod-shaped centrosomes, each with its radiations, were observed 
close together, and in such a position as to form a wide V, giving the 
impression that a longitudinal division of the single centrosome had 
taken place. The manner in which a cluster of radiations is attached 
to each daughter centrosome seems to lend weight to-this conclusion. 
The daughter centrosomes now separate, moving along the nuclear 
membrane, but they do not, as in the first mitosis, traverse an angular 
distance of 180° before the formation of the spindle begins (Fig. 3, 
I,K). The development of the spindle is the same as in the first 
mitosis, as Fig. 3, I, J, K, L, will clearly show. 
In other brown alge, so far as known (Swingle ’97, Strasburger 97), 
1 This massing of the chromosomes may not occur in all cases. 
