xiv TEXT-FIGURES 



FIG. 



13. Diagram illustrating JANSSENS' hypothesis of chias- 



matypy . . . . . . 



14. Diagram of a spermatozoon . . . . . 



15. Verson's cell in testis of Pieris ..... 



1 6. Fertilisation by second polar nucleus in artificially par- 



thenogenetic egg of a Star-fish, after BUCHNER 



17. Chromosome-groups in the Gall-fly Neuroterus 



1 8. Compound groups formed by union of the ^-chromosome 



with other chromosomes in Orthoptera, from WILSON 



19. Chromosomes in the maturation of the eggs of Moths, 



after SEILER and DONCASTER ..... 



20. Early development of the egg of Litomastix, after SIL 



VESTRI ......... 



21. Development of oocytes and nurse-cells in Dytiscus, after 



GiJNTHERT ........ 



22. Differentiation of a Sertoli cell from spermatogonia in 



Man, after MONTGOMERY 



23. Persistence of abnormal chromosome number in seg- 



mentation of egg of Ascaris, from BOVERI 



24. Nuclei in segmentation of the egg of A scaris, from BOVERI 



25 . Chromosomes emerging from nuclear network in spermato- 



gonia and spermatocytes of Hemiptera, from WILSON 



26. Diagram of distribution of chromosomes on a quadripolar 



spindle, from BOVERI ...... 



27. "Partially thelykaryotic " pluteus of Echinoid hybrid, 



from MEREST ........ 



28. Diagrams illustrating the hypothesis of "crossing-over," 



from MORGAN . . . 



29. Chromosome groups of Drosophila showing non -disjunc- 



tion, from original drawings by BRIDGES 



30. Eggs of Nereis segmenting normally and under pressure, 



from WILSON . . . 



31. Segmentation of centrifuged eggs of Arbacia, from 



MORGAN 



