The Chromosomes of Euschistus variolarius, Euschistus servus etc. 497 
cessitates their presence in all the spermatozoa of both sexes, thus giving 
to the so-called female-producing Spermatozoon the male-producing fac- 
tors in addition to the female-producing factors. The female-producing 
Spermatozoon is therefore heterozygous for sex and the male-producing 
Spermatozoon honiozygous for sex”. 
“If we assume with Morgan that both members of a definite diploid 
pair of chromosomes contain the factors for producing a male, this must 
hold for the same diploid pair in both the female and the male, and if 
the factors producing exclusively male characters are linked with the 
factors for maleness, then each meniber of this diploid pair should 
contain the factors for producing the spot, which in E. variolarius is 
an exclusively male character. 
As this diploid pair is in the female as well as in the male, it would 
seem necessary to assume that in E. variolarius the female carries an in- 
hibitor of such exclusively male characters. But one is embarassed in 
considering where to place this inhibitor; if we locate itin both members 
of an homologous pair of chromosomes, then it would be in the male as 
well as in the female. If we place it in only one member of an homolo- 
gous pair (in A, for example, of text fig. 2), this would involve selective 
fertilization, for if the female is fertilized by the so-called female-produ- 
cing Spermatozoon that is without the A, and she has by chance discarded 
the other A in her polar body, she also would have the spot, and further, 
half the male-producing spermatozoa have the A chromosome and there- 
fore they must not function or the spot would be absent in half the vario- 
larius males. 
If we place the inhibitor in the three X chromosomes, the assumption 
obviously would not work, for the male has one of the three X chromo- 
somes and the spot would therefore be inhibited in the male as well as 
in the female. It would therefore be necessary to assume that in E. 
variolarius two doses of inhibitor are necessary to cancel the spot. This 
assumption, which apparently would hold for E. variolarius, is, however, 
found to be untenable if used to explain the results of the cross between 
E. variolarius and E. servus, for the female hybrid cannot receive a double 
dose unless we assume that E. servus carries an inhibitor for inhibiting 
in the female a male character which is never present in the male. If, 
however, we feel justified in assuming that the female hybrid has a 
double dose of inhibitor, this would fall to explain the absence of the 
spot in those male hybrids, which do not have it, for they have only 
one X chromosome and therefore only one dose of inhibitor. AVe might 
avoid this by assuming that one dose only would be necessary for the 
