294 FRANZ SCHRADER 
male has | X, irrespective of whether the sex chromatin is carried 
in a single chromosome or not. As far as this chromatin is con- 
cerned, such a case does not differ from that of a typical hemip- 
teron with an unmated sex chromosome. No evidence is avail-— 
able that there is in these cases a distinct and separate X element, 
but in this connection it might be pointed out that coupling of 
this chromosome with a certain autosome has been observed in a 
number of cases (Sinety, in Leptynia, ’02; McClung, in Orthop- 
tera, ’05; Boveri, 09, and Frolowa, ’12, in Ascaris, ete.) 
Neither is the sex chromosome necessarily a single element, as 
Payne (’12) has pointed out especially in the reduviids. It is 
thus very possible that each autosome carries a certain amount 
of sex chromatin. The fact that in the diploid complex the auto- 
somes are doubled as well as the sex chromosomes, if such a condi- 
tion prevails, and that therefore the proportional relation remains 
unaltered, may indicate only that the two kinds of chromatin 
are independent of each other as far as influence on development 
is concerned. This does not imply that development could pro- 
ceed in the absence of either of the two kinds of chromatin. It 
is probable that the autosomal chromatin is active in the causa- 
tion of sex as well as in the development of all other characters, 
but this effect is irrespective of its amount involved. At a cer- 
tain point, however, a decisive factor appears in the influence 
of the sex chromatin, and this influence, given the conditions 
already established by the autosomal chromatin, appears to 
depend on its quantity. 
SUMMARY 
1. Trialeurodes vaporariorum has two races which differ in 
their parthenogenetic behavior in that the English race gives 
rise to females and the American to males. 
2. In the American race all eggs give off two polar bodies and 
undergo reduction. 
3. Eggs that are not fertilized develop with the haploid num- 
ber of chromosomes and produce males. Those which are fer- 
tilized regain the diploid complex and give rise to females. 
