INHERITANCE OF SEX AND RELATED PHENOMENA 211 
possess the diploid number of chromosomes and drones the haploid 
number. By means of experimental investigations on the sex ratio 
A. F. Shull has recently shown that sex-determination in the mullein 
thrips, Anthothrips verbasci, is accomplished by the same method as in 
the honey bee, 7.e., females have the diploid number and males the 
haploid number of chromosomes. 
Morgan has worked out in detail the complex type of chromosome 
relations obtaining in the inheritance of sex in the hickory phylloxeran, 
1st Generation 
Xx Xx Xx Xx’ 
Stem Mother-Female Producing Line Stem Mother-Male Producing Line. 
rae Xx Xv’ 
AX 
| Polar Spiudles | | 
f | 
Xx Xx Stem Motber’s Eggs Xx Xx’ 
—A 
2nd Generation 
Xx Xx Xx Xx’ 
Migrant-Female Producer Migrant-Male Producer 
XOX xx’ 
XxXx Wey. Xx 
| | I | Polar Spindles | | | 
Xx Xx Xx xXx’ 
Female Egg Male Eggs 
8rd Generation 
Xx Xx 2 eX Xx’ 
Female “Male-Typel Male-Type II 
Female Producing 
Sperm 
x fe ON 
| x Polar Spindle 
Degenerate’ 
Xx Se ey, 
Sexual Egg 
Fig. 95.—Diagram to illustrate the chromosomal cycle of Phylloxera caryecaulis, 
(After Morgan.) 
Phylloxera caryecaulis. The life cycle of this insect with respect to the 
chromosome cycles is shown in diagram in Fig. 95. There are eight 
chromosomes in this phylloxeran and of these four appear to be con- 
nected with the determination of sex. They are the only ones illustrated 
in the diagram. Beginning with the stem mothers at the top of the 
diagram, these emerge in the spring from fertilized eggs. They immedi- 
ately attach themselves to the hickory leaves, thereby causing a gall 
to be formed around them, and in this gall they lay their eggs. As 
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