494 
Katharine Foot and E. C. Strobell 
chromosome that can be in both so-called male-procliicing spernia- 
tozoa. 
The two types of spermatozoa demoiistrated in the diagram, i. e. 
those having the Y clnomosome and those having the X clu-oniosome, 
have given rise to the assumption that such a morphological difference 
involves an important functional difference, viz. when the spermatozoa 
which contain this Y cliromosome fertilize the eggs, niales are produced 
and when the spermatozoa which contain the X chromosome fertilize 
the eggs, females are produced. These so-called male- and female-pro- 
ducing spermatozoa are supposed to carry the factors which determine sex. 
A belief in the fundamental significance of the chromosomes — that 
they are the bearers and distributors of unit factors — leads logically 
to very defhiite conclusions that may be tested by experiment. 
Of the Y chromosome Castle ('09) said: 
“1 would off er the Suggestion that we have a mechanism suitable 
for the transmission of characters exclusively male in the Y element 
described by YTlsox, the ‘synaptic mate’ of the X element”. 
Of the X chromosome Morgax (TI) said: “YTiat is most important 
is the discovery that the X chromosome contains not only one of the 
essential factors in sex determination ; but also all other characters that 
are sex-limited in inheritance”. 
Experimental Ijreeding with the aim of studying the transmission 
of such an exclusively male character as the genital spot of variolarius 
should be able to determine whether the X or A" chromosome is necessary 
to the transmission of such an exclusively male character, and we believe 
that the answer to this question will give significant evidence for or against 
the assumption that these two so-called sex chromosomes are the bearers 
of factors essential to the determination of sex. It is certainly logical 
to believe that if a given chromosome carries the factors that mould a 
definite Segment of these insects into the form essential to the functioning 
of the male genital organs, that the factors for a definite pigmented spot 
011 the same segment are carried by the same chromosome. The spot is 
a character that is as exclusively male as the genital organ itself and it 
is not logical to assume that the two characters have a different mode 
of transmission. We therefore claim the right to assume that if the results 
of our experiments show that the genital spot can be transmitted without 
the aid of either the Y or the X chromosome, it is a clear indication that 
the male genital organs themselves are transmitted independently of 
these chromosomes and therefore the assumption of sex-determining 
chromosomes in these insects does not stand the test of experiment. 
