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, i.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, 



XxXx 



1st Generation 



XxXx 



Stem Mother- Female Producing Liue Stem Mother Male Producing Line 



I'olar Spindle, 



of 

 Stem Mother's Eggs 



2nd Generation 



XxXx 



Migrant-female Producer 



XxXx 



Migrant -Male Producer 



XX xx' 



XxXx 



Female Egg 



Polar Spindle) 



Xx 

 Xx 



Xx' 



Male Eggs 



XxXj 



Female 



3rd Generation 



Xx Xx' 



Male-Type I Male-Type II 



Female Producing 



Sperm 



Polar Spindle 



Xx 



Sexual Egg 



FIG. 95. Diagram to illustrate the chromosomal cycle of Phylloxera carycecaulis. 



(After Morgan.) 



Phylloxera carycecaulis. 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 



