ILLUSTRATIONS 



Fig. page 



1 . Cross Between a Tall and a Short Race of Garden Peas 20 



2. Cross Between WTiite and Red Flowered Four-o'clocks 24 



3. Cross Between Splashed-WTiite and Black, in Andalusian 26 



4. Male and Female Vinegar Fly 28 



5. Normal and Abnormal Abdomen of D. melanogaster 29 



6. Relation of Black Body Color to Wild Type as Shown by Classes 



of Fhes 30 



7. Normal, Heterozygous, and Bar Eye of the Vinegar Fly 31 



8. Relation of Bar Eye to Normal Eye 31 



9. Relation of Andalusian to Splashed White and to Black as Shown 



by Classes of Birds 32 



10. Relation of Tall to Short Peas 32 



11. Relation of Normal to Abnormal Abdomen as Shown by Classes 



of Flies 32 



12. Relation of Normal to Duplicate Legs of Flies 33 



13. Notch Wings in the Vinegar Fly 35 



14. Oocyte of Ancyracanthus; Growth Period; Nucleus with Tetrads. . . 40 



15. Egg of Ancyracanthus 40 ■ 



16. Eggs of Ancyracanthus within Membrane 41 



17. Spermatogenesis of Ancyracanthus 42 



18. Last Spermatogonial Division of Tomopteris and Stages Before and 



During Synapsis 45 



19. Thin-Thread Stage of Tomopteris Spermatoc5^e ; Tetrads, and First 



and Second Spermatocyte Divisions 47 



20. Synaptic Stages and Those Immediately Following in Batracoseps ... 48 



21. Synaptic Stages and Those Immediately Following in the Egg of 



Pristiurus 50 



22. Sister Blastomeres of Ascaris Preparatory to Another Division .... 52 



23. Normal and Reduced Chromosomes of Biston 53 



24. Division Figures in Egg of Ctenolabrus Fertihzed by Fundulus 54 



25. Female and Male Chromosome Groups of Protenor 55 



26. Reduced Chromosome Group; and Extrusion of Polar Bodies in 



Protenor ^^ 



9 



