480 T. H. MORGAN 
The main points that were described in my previous papers 
may be summarized as follows: 
1. Two classes of sperm are produced in the male differing in 
the presence and absence of a pair of chromosomes. One class of 
sperm degenerates. It corresponds to the male-producing class 
of otherinsects. The other class produces functional spermatoza 
which entering the egg give rise to females only. These sperm 
correspond to the female-producing class of other insects. 
2. The male-producing egg contains one less chromosome after 
the extrusion of its single polar body than it contained before 
this event. In a preliminary note (10) I have stated how this 
elimination takes place and in the present paper I bring forward 
the evidence on which this statement was based. 
3. The difference in size between the male-producing and 
the female-producing egg, before the former has extruded its 
polar body, proves that the predetermination of the males ante- 
dates the extrusion of the chromosome in, the polar body of the 
(smaller) male-producing egg. 
4. More male-producing individuals are the descendants of 
each stem-mother than female-producing individuals. The stem- 
mother must give rise to two kinds of eggs, i. e., they must be 
different either before or after the polar body is extruded. The 
factor that differentiates these two kinds of eggs, was not dis- 
covered. It is this point that the evidence now brought forward 
may I hope help to elucidate. 
THE DIFFERENCES IN THE CHROMOSOME GROUPS IN THE POLAR 
SPINDLES OF THE STEM-MOTHER’S EGG AND OF THE 
MALE AND FEMALE-PRODUCING EGGS 
In my former paper (’09) I have figured ten equatorial plates 
of polar spindles of the eggs produced by the stem-mother. In 
all of these the sex chromosomes are of nearly the same size. In 
two other plates one chromosome is much smaller than the others, 
which is probably due to this chromosome having been cut by 
the knife. Failure to find the missing piece in the next section 
would not be significant, since it might be very difficult to find 
such a piece in the egg filled with yolk granules of about the same 
