ELIMINATION OF SEX CHROMOSOMES 483 
THE DIVISION OF THE POLAR SPINDLE IN THE MALE- AND 
IN THE FEMALE-PRODUCING EGGS 
A brief abstract of the results given in this section was pub- 
lished in the Proceedings of the Society of Experimental Biology 
and Medicine* for May, 1910. In order to study the division 
of the polar spindle a large amount of new material was collected 
in the summer of 1909 which was cut and studied during the 
following winter. It has been most laborious to find eggs in 
which the polar spindle was in the process of division, and I 
wish to express my obligations to my assistant, Miss E. M. Wal- 
lace, who has found most of the new cases here figured. 
In my former paper (09) I described the anaphase of two 
eggs that seemed to be female eggs (see below), but none of the 
male eggs; and it is the latter that would be expected to give the 
critical evidence. This evidence was briefly stated in my prelim- 
inarynotein 1910. [shall nowgive drawings of several anaphases 
of male eggs that show beyond doubt that a lagging chromosome 
is present; that it passes to the outer pole, and forms a separate 
vesicle in the polar body. 
The first case is shown in fig. 5 representing an anaphase of 
the polar spindle. Five chromosomes lie at the outer pole and 
five at the inner pole. In the middle of the spindle lies a double 
chromosome. It is relatively large and its two halves appear 
somewhat unequal. For reasons that appear later I shall speak 
of this as a single chromosome that has already divided into 
halves. 
The second case is shown in fig. 6. Here also five chromosomes, 
somewhat elongated, lie at the outer pole and five at the inner 
pole of the spindle. In the middle of the spindle there is a 
double chromosome, its halves equal as far as can be determined. 
The third case is shown in fig. 7. It represents a later stage; 
the polar body being in process of constricting from the egg. 
The group of chromosomes at the outer pole is now in process 
of division. Five chromosomes can be recognized, two dividing, 
and three having completed their division. At the inner pole 
3 Proc. Soc. Exp. Biology and Medicine, vol. 7, 1910. 
