xiv TEXT-FIGURES 



FIG. PAGE 



13. Diagram illustrating JANSSENS' hypothesis of chias- 



matypy ......... 90 



14. Diagram of a spermatozoon ...... 92 



15. Verson's cell in testis of Pieris ..... 104 



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



thenogenetic egg of a Star-fish, after BUCHNER . 130 



17. Chromosome-groups in the Gall-fly Neuroterus . . 153 



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



with other chromosomes in Orthoptera, from WILSON 161 



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



after SEILER and DONCASTER . . . . .170 



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



VESTRI 181 



2 1 . Development of oocy tes and nurse-cells in Dytiscus, after 



GUNTHERT ........ 184 



22. Differentiation of a Sertoli cell from spermatogonia in 



Man, after MONTGOMERY , . . . . .185 



23. Persistence of abnormal chromosome number in seg- 



mentation of egg of Ascaris, from BOVERI . . 191 



24. Nuclei in segmentation of the egg of A scaris, from BOVERI 194 



25. Chromosomes emerging from nuclear network in spermato- 



gonia and spermatocytes of Hemiptera, from WILSON 197 



26. Diagram of distribution of chromosomes on a quadripolar 



spindle, from BOVERI ...... 202 



27. "Partially thelykaryotic " pluteus of Echinoid hybrid, 



from HERBST ........ 209 



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



from MORGAN . 226 



29. Chromosome groups of Drosophila showing non-disjunc- 



tion, from original drawings by BRIDGES . . 233 



30. Eggs of Nereis segmenting normally and under pressure, 



from WILSON 246 



31. Segmentation of centrifuged eggs of Arbacia, from 



MORGAN 250 



