418 Experimental Zovlogy 
part — is used in the formation of the tail of the spermatozoén, 
which may or may not enter the egg; but some of the cyto- 
plasm forms at least the centrosome and is carried into the egg. 
Owing to our inability to follow the history of this cytoplasm 
in the egg, we have come to ignore its existence, while the nucleus 
that can be easily traced has occupied exclusively the attention of 
modern embryologists with rare exceptions. 
If we admit that the cytoplasm of the spermatozoGn is not only 
brought into the egg, but slowly increases in quantity there, can 
we find any clew in such a condition that will help in the solu- 
tion of the problem of sex determination? There are several 
possibilities that should be considered. If we suppose that there 
is predetermined male and female cytoplasm in the egg or 
the spermatozo6n, or in both, we encounter precisely the same 
difficulties that have been met with by assuming that predeter- 
mined elements of these two kinds exist in the nucleus. From 
this point of view the two assumptions stand on the same footing. 
If we assume that the determination of sex lies in the cytoplasm, 
not in the form of predetermined elements male and female, 
but as one of the alternative conditions of differentiation of the 
cytoplasm, we must still explain what factors — external or in- 
ternal — determine whether the one or the other condition shall 
dominate. Whether this is due at times to a relation between 
the chromatin and the cytoplasm, or at other times to a relation 
depending on the condition of nourishment of the cytoplasm, 
etc., cannot be stated. However probable it might be made to 
appear that the differentiation that appears in the cytoplasm 
really originates there, and not in the nucleus (except in so far 
as the latter induces important changes in the cytoplasm through 
its assimilative changes), the fact remains that we cannot ex- 
plain the mechanism in the cytoplasm through which the one or 
the other condition comes to be the dominating one. Here, as in 
the case of the nucleus, we are too ignorant at present of the real 
chemical changes that take place to permit of more than purely 
speculative views. 
Ziegler has recently proposed an hypothesis of sex determina- 
