ILLUSTRATIONS 



1. Chromosomes in the condensed condition 8 



2. Successive stages in the division of chromo- 



somes 9 



3. Male and female groups of chromosomes in 



Protenor 14 



4. Chromosome combinations in the formation 



of germ cells 16 



5. Chromosome combinations in fertilization 17 



6. Male and female groups of chromosomes in 



Lygaeus 19 



7. Male and female groups of chromosomes in 



the fruit-fly 20 



8. The fruit-fly 24 



9. Inheritance of bar-eye and normal eye in 



Drosophila 25 



10. Inheritance of eyes in Drosophila 27 



11. Inheritance of recessive characteristic 30 



vu 



