225 
from the anaphase of the last spermatogonial division until it is appor- 
tioned to two of the four spermatids arising from each first spermato- 
cyte. So far as I can learn, we have no knowledge of an ordinary 
chromosome regularly dividing more than once without going into a 
resting stage between divisions. Why, then, should we expect this 
spermatogonial chromosome which has passed over into the spermato- 
cytes to divide more than once? 
PAULMIER makes his theory possible by considering the acces- 
sory chromosome a tetrad, but in this he is certainly mistaken. The 
accessory chromosome may, and sometines does, divide into its two 
chromatids during the telophase of the last spermatogonial division 
and thus comes over into the first spermatocyte double, but the chro- 
matids are the halves of an ordinary spermatogonial chromosome, and 
are not comparable to the elements of a tetrad. It is to be noted in 
this connection that the evidence afforded by Orthopteran material 
is much clearer and more definite than that derived from the sper- 
matogonia of the Hemiptera, so that PAULMIER’S error is not re- 
markable. 
Being convinced from the behavior in the spermatogonia and the 
first spermatocytes of the primary importance of the accessory chromo- 
some, and attracted by the unusual method of its participation in 
the spermatocyte mitoses, I sought an explanation that would be 
commensurate with the importance of these facts. Upon the as- 
sumption that there is a qualitative difference between the various 
chromosomes of the nucleus, it would necessarily follow that there 
are formed two kinds of spermatozoa which, by fertilization of the 
egg, would produce individuals qualitatively different. Since the number 
of each of these varieties of spermatozoa is the same, it would happen 
that there would be an approximately equal number of these two 
kinds of offspring. We know that the orly quality which separates 
the members of a species into these two groups is that of sex. I 
therefore came to the conclusion that the accessory chromosome is 
the element which determines that the germ cells of the embryo 
shall continue their development past the slightly modified egg cell 
into the highly specialized spermatozoon. 
It would not be desirable in a preliminary paper of this character 
to extend it by a detail of the discussion by which the problem was 
considered. Suffice it to say that by this assumption it is possible to recon- 
cile the resus of mltany empirical theories which have proved measur- 
ably true upon the general ground that the egg is placed in a deli- 
cate adjustment with its environment, and in response to this, is able 
Anat, Anz. XX. Aufsätze, 15 
